Release: 2.1.0b1 | Release Date: January 21, 2026

# SQLAlchemy 2.1 Documentation

# 1.2 Changelog

## 1.2.19

Released: April 15, 2019

### orm

- [orm] [bug]

  Fixed a regression in 1.2 due to the introduction of baked queries for relationship lazy loaders, where a race condition is created during the generation of the “lazy clause” which occurs within a memoized attribute. If two threads initialize the memoized attribute concurrently, the baked query could be generated with bind parameter keys that are then replaced with new keys by the next run, leading to a lazy load query that specifies the related criteria as `None`. The fix establishes that the parameter names are fixed before the new clause and parameter objects are generated, so that the names are the same every time.

  References: #4507

### examples

- [examples] [bug]

  Fixed bug in large_resultsets example case where a re-named “id” variable due to code reformatting caused the test to fail. Pull request courtesy Matt Schuchhardt.

  References: #4528

### engine

- [engine] [bug]

  Comparing two objects of `URL` using `__eq__()` did not take port number into consideration, two objects differing only by port number were considered equal. Port comparison is now added in `__eq__()` method of `URL`, objects differing by port number are now not equal. Additionally, `__ne__()` was not implemented for `URL` which caused unexpected result when `!=` was used in Python2, since there are no implied relationships among the comparison operators in Python2.

  References: #4406

### mssql

- [mssql] [bug]

  A commit() is emitted after an isolation level change to SNAPSHOT, as both pyodbc and pymssql open an implicit transaction which blocks subsequent SQL from being emitted in the current transaction.

  References: #4536

### oracle

- [oracle] [bug]

  Added support for reflection of the `NCHAR` datatype to the Oracle dialect, and added `NCHAR` to the list of types exported by the Oracle dialect.

  References: #4506

## 1.2.18

Released: February 15, 2019

### orm

- [orm] [bug]

  Fixed a regression in 1.2 where a wildcard/load_only loader option would not work correctly against a loader path where of_type() were used to limit to a particular subclass. The fix only works for of_type() of a simple subclass so far, not a with_polymorphic entity which will be addressed in a separate issue; it is unlikely this latter case was working previously.

  References: #4468

- [orm] [bug]

  Fixed fairly simple but critical issue where the `SessionEvents.pending_to_persistent()` event would be invoked for objects not just when they move from pending to persistent, but when they were also already persistent and just being updated, thus causing the event to be invoked for all objects on every update.

  References: #4489

### sql

- [sql] [bug]

  Fixed issue where the `JSON` type had a read-only `JSON.should_evaluate_none` attribute, which would cause failures when making use of the `TypeEngine.evaluates_none()` method in conjunction with this type. Pull request courtesy Sanjana S.

  References: #4485

### mysql

- [mysql] [bug]

  Fixed a second regression caused by #4344 (the first was #4361), which works around MySQL issue 88718, where the lower casing function used was not correct for Python 2 with OSX/Windows casing conventions, which would then raise `TypeError`. Full coverage has been added to this logic so that every codepath is exercised in a mock style for all three casing conventions on all versions of Python. MySQL 8.0 has meanwhile fixed issue 88718 so the workaround is only applies to a particular span of MySQL 8.0 versions.

  References: #4492

### sqlite

- [sqlite] [bug]

  Fixed bug in SQLite DDL where using an expression as a server side default required that it be contained within parenthesis to be accepted by the sqlite parser. Pull request courtesy Bartlomiej Biernacki.

  References: #4474

### mssql

- [mssql] [bug]

  Fixed bug where the SQL Server “IDENTITY_INSERT” logic that allows an INSERT to proceed with an explicit value on an IDENTITY column was not detecting the case where `Insert.values()` were used with a dictionary that contained a `Column` as key and a SQL expression as a value.

  References: #4499

## 1.2.17

Released: January 25, 2019

### orm

- [orm] [feature]

  Added new event hooks `QueryEvents.before_compile_update()` and `QueryEvents.before_compile_delete()` which complement `QueryEvents.before_compile()` in the case of the `Query.update()` and `Query.delete()` methods.

  References: #4461

- [orm] [bug]

  Fixed issue where when using single-table inheritance in conjunction with a joined inheritance hierarchy that uses “with polymorphic” loading, the “single table criteria” for that single-table entity could get confused for that of other entities from the same hierarchy used in the same query.The adaption of the “single table criteria” is made more specific to the target entity to avoid it accidentally getting adapted to other tables in the query.

  References: #4454

### postgresql

- [postgresql] [bug]

  Revised the query used when reflecting CHECK constraints to make use of the `pg_get_constraintdef` function, as the `consrc` column is being deprecated in PG 12. Thanks to John A Stevenson for the tip.

  References: #4463

### oracle

- [oracle] [bug]

  Fixed regression in integer precision logic due to the refactor of the cx_Oracle dialect in 1.2. We now no longer apply the cx_Oracle.NATIVE_INT type to result columns sending integer values (detected as positive precision with scale ==0) which encounters integer overflow issues with values that go beyond the 32 bit boundary. Instead, the output variable is left untyped so that cx_Oracle can choose the best option.

  References: #4457

## 1.2.16

Released: January 11, 2019

### engine

- [engine] [bug]

  Fixed a regression introduced in version 1.2 where a refactor of the `SQLAlchemyError` base exception class introduced an inappropriate coercion of a plain string message into Unicode under python 2k, which is not handled by the Python interpreter for characters outside of the platform’s encoding (typically ascii). The `SQLAlchemyError` class now passes a bytestring through under Py2K for `__str__()` as is the behavior of exception objects in general under Py2K, does a safe coercion to unicode utf-8 with backslash fallback for `__unicode__()`. For Py3K the message is typically unicode already, but if not is again safe-coerced with utf-8 with backslash fallback for the `__str__()` method.

  References: #4429

### sql

- [sql] [bug] [mysql] [oracle]

  Fixed issue where the DDL emitted for `DropTableComment`, which will be used by an upcoming version of Alembic, was incorrect for the MySQL and Oracle databases.

  References: #4436

### postgresql

- [postgresql] [bug]

  Fixed issue where a `ENUM` or a custom domain present in a remote schema would not be recognized within column reflection if the name of the enum/domain or the name of the schema required quoting. A new parsing scheme now fully parses out quoted or non-quoted tokens including support for SQL-escaped quotes.

  References: #4416

- [postgresql] [bug]

  Fixed issue where multiple `ENUM` objects referred to by the same `MetaData` object would fail to be created if multiple objects had the same name under different schema names. The internal memoization the PostgreSQL dialect uses to track if it has created a particular `ENUM` in the database during a DDL creation sequence now takes schema name into account.

### sqlite

- [sqlite] [bug]

  Reflection of an index based on SQL expressions are now skipped with a warning, in the same way as that of the Postgresql dialect, where we currently do not support reflecting indexes that have SQL expressions within them. Previously, an index with columns of None were produced which would break tools like Alembic.

  References: #4431

### misc

- [no_tags]

  Fixed issue in “expanding IN” feature where using the same bound parameter name more than once in a query would lead to a KeyError within the process of rewriting the parameters in the query.

  References: #4394

## 1.2.15

Released: December 11, 2018

### orm

- [orm] [bug]

  Fixed bug where the ORM annotations could be incorrect for the primaryjoin/secondaryjoin a relationship if one used the pattern `ForeignKey(SomeClass.id)` in the declarative mappings. This pattern would leak undesired annotations into the join conditions which can break aliasing operations done within `Query` that are not supposed to impact elements in that join condition. These annotations are now removed up front if present.

  References: #4367

- [orm] [bug]

  In continuing with a similar theme as that of very recent #4349, repaired issue with `Comparator.any()` and `Comparator.has()` where the “secondary” selectable needs to be explicitly part of the FROM clause in the EXISTS subquery to suit the case where this “secondary” is a `Join` object.

  References: #4366

- [orm] [bug]

  Fixed regression caused by #4349 where adding the “secondary” table to the FROM clause for a dynamic loader would affect the ability of the `Query` to make a subsequent join to another entity. The fix adds the primary entity as the first element of the FROM list since `Query.join()` wants to jump from that. Version 1.3 will have a more comprehensive solution to this problem as well (#4365).

  References: #4363

- [orm] [bug]

  Fixed bug where chaining of mapper options using `RelationshipProperty.of_type()` in conjunction with a chained option that refers to an attribute name by string only would fail to locate the attribute.

  References: #4400

### orm declarative

- [orm] [declarative] [bug]

  A warning is emitted in the case that a `column()` object is applied to a declarative class, as it seems likely this intended to be a `Column` object.

  References: #4374

### misc

- [no_tags]

  Added support for the `write_timeout` flag accepted by mysqlclient and pymysql to be passed in the URL string.

  References: #4381

- [no_tags]

  Fixed issue where reflection of a PostgreSQL domain that is expressed as an array would fail to be recognized. Pull request courtesy Jakub Synowiec.

  References: #4377, #4380

## 1.2.14

Released: November 10, 2018

### orm

- [orm] [bug]

  Fixed bug in `Session.bulk_update_mappings()` where alternate mapped attribute names would result in the primary key column of the UPDATE statement being included in the SET clause, as well as the WHERE clause; while usually harmless, for SQL Server this can raise an error due to the IDENTITY column. This is a continuation of the same bug that was fixed in #3849, where testing was insufficient to catch this additional flaw.

  References: #4357

- [orm] [bug]

  Fixed a minor performance issue which could in some cases add unnecessary overhead to result fetching, involving the use of ORM columns and entities that include those same columns at the same time within a query. The issue has to do with hash / eq overhead when referring to the column in different ways.

  References: #4347

### mysql

- [mysql] [bug]

  Fixed regression caused by #4344 released in 1.2.13, where the fix for MySQL 8.0’s case sensitivity problem with referenced column names when reflecting foreign key referents is worked around using the `information_schema.columns` view. The workaround was failing on OSX / `lower_case_table_names=2` which produces non-matching casing for the `information_schema.columns` vs. that of `SHOW CREATE TABLE`, so in case-insensitive SQL modes case-insensitive matching is now used.

  References: #4361

## 1.2.13

Released: October 31, 2018

### orm

- [orm] [bug]

  Fixed bug where “dynamic” loader needs to explicitly set the “secondary” table in the FROM clause of the query, to suit the case where the secondary is a join object that is otherwise not pulled into the query from its columns alone.

  References: #4349

### orm declarative

- [orm] [declarative] [bug]

  Fixed regression caused by #4326 in version 1.2.12 where using `declared_attr` with a mixin in conjunction with `synonym()` would fail to map the synonym properly to an inherited subclass.

  References: #4350

- [orm] [declarative] [bug]

  The column conflict resolution technique discussed at Resolving Column Conflicts with use_existing_column is now functional for a `Column` that is also a primary key column. Previously, a check for primary key columns declared on a single-inheritance subclass would occur before the column copy were allowed to pass.

  References: #4352

### sql

- [sql] [feature]

  Refactored `SQLCompiler` to expose a `SQLCompiler.group_by_clause()` method similar to the `SQLCompiler.order_by_clause()` and `SQLCompiler.limit_clause()` methods, which can be overridden by dialects to customize how GROUP BY renders. Pull request courtesy Samuel Chou.

- [sql] [bug]

  Fixed bug where the `Enum.create_constraint` flag on the `Enum` datatype would not be propagated to copies of the type, which affects use cases such as declarative mixins and abstract bases.

  References: #4341

### postgresql

- [postgresql] [bug]

  Added support for the `aggregate_order_by` function to receive multiple ORDER BY elements, previously only a single element was accepted.

  References: #4337

### mysql

- [mysql] [bug]

  Added word `function` to the list of reserved words for MySQL, which is now a keyword in MySQL 8.0

  References: #4348

- [mysql] [bug]

  Added a workaround for a MySQL bug #88718 introduced in the 8.0 series, where the reflection of a foreign key constraint is not reporting the correct case sensitivity for the referred column, leading to errors during use of the reflected constraint such as when using the automap extension. The workaround emits an additional query to the information_schema tables in order to retrieve the correct case sensitive name.

  References: #4344

### misc

- [misc] [bug]

  Fixed issue where part of the utility language helper internals was passing the wrong kind of argument to the Python `__import__` builtin as the list of modules to be imported. The issue produced no symptoms within the core library but could cause issues with external applications that redefine the `__import__` builtin or otherwise instrument it. Pull request courtesy Joe Urciuoli.

- [misc] [bug] [py3k]

  Fixed additional warnings generated by Python 3.7 due to changes in the organization of the Python `collections` and `collections.abc` packages. Previous `collections` warnings were fixed in version 1.2.11. Pull request courtesy xtreak.

  References: #4339

- [bug] [ext]

  Added missing `.index()` method to list-based association collections in the association proxy extension.

## 1.2.12

Released: September 19, 2018

### orm

- [orm] [bug]

  Added a check within the weakref cleanup for the `InstanceState` object to check for the presence of the `dict` builtin, in an effort to reduce error messages generated when these cleanups occur during interpreter shutdown. Pull request courtesy Romuald Brunet.

- [orm] [bug]

  Fixed bug where use of `Lateral` construct in conjunction with `Query.join()` as well as `Query.select_entity_from()` would not apply clause adaption to the right side of the join. “lateral” introduces the use case of the right side of a join being correlatable. Previously, adaptation of this clause wasn’t considered. Note that in 1.2 only, a selectable introduced by `Query.subquery()` is still not adapted due to #4304; the selectable needs to be produced by the `select()` function to be the right side of the “lateral” join.

  References: #4334

- [orm] [bug]

  Fixed 1.2 regression caused by #3472 where the handling of an “updated_at” style column within the context of a post-update operation would also occur for a row that is to be deleted following the update, meaning both that a column with a Python-side value generator would show the now-deleted value that was emitted for the UPDATE before the DELETE (which was not the previous behavior), as well as that a SQL- emitted value generator would have the attribute expired, meaning the previous value would be unreachable due to the row having been deleted and the object detached from the session.The “postfetch” logic that was added as part of #3472 is now skipped entirely for an object that ultimately is to be deleted.

  References: #4327

### orm declarative

- [orm] [declarative] [bug]

  Fixed bug where the declarative scan for attributes would receive the expression proxy delivered by a hybrid attribute at the class level, and not the hybrid attribute itself, when receiving the descriptor via the `@declared_attr` callable on a subclass of an already-mapped class. This would lead to an attribute that did not report itself as a hybrid when viewed within `Mapper.all_orm_descriptors`.

  References: #4326

### postgresql

- [postgresql] [bug]

  Fixed bug in PostgreSQL dialect where compiler keyword arguments such as `literal_binds=True` were not being propagated to a DISTINCT ON expression.

  References: #4325

- [postgresql] [bug]

  Fixed the `array_agg()` function, which is a slightly altered version of the usual `array_agg()` function, to also accept an incoming “type” argument without forcing an ARRAY around it, essentially the same thing that was fixed for the generic function in 1.1 in #4107.

  References: #4324

- [postgresql] [bug]

  Fixed bug in PostgreSQL ENUM reflection where a case-sensitive, quoted name would be reported by the query including quotes, which would not match a target column during table reflection as the quotes needed to be stripped off.

  References: #4323

### oracle

- [oracle] [bug]

  Fixed issue for cx_Oracle 7.0 where the behavior of Oracle param.getvalue() now returns a list, rather than a single scalar value, breaking autoincrement logic throughout the Core and ORM. The dml_ret_array_val compatibility flag is used for cx_Oracle 6.3 and 6.4 to establish compatible behavior with 7.0 and forward, for cx_Oracle 6.2.1 and prior a version number check falls back to the old logic.

  References: #4335

### misc

- [bug] [ext]

  Fixed issue where `BakedQuery` did not include the specific query class used by the `Session` as part of the cache key, leading to incompatibilities when using custom query classes, in particular the `ShardedQuery` which has some different argument signatures.

  References: #4328

## 1.2.11

Released: August 20, 2018

### orm declarative

- [orm] [declarative] [bug]

  Fixed issue in previously untested use case, allowing a declarative mapped class to inherit from a classically-mapped class outside of the declarative base, including that it accommodates for unmapped intermediate classes. An unmapped intermediate class may specify `__abstract__`, which is now interpreted correctly, or the intermediate class can remain unmarked, and the classically mapped base class will be detected within the hierarchy regardless. In order to anticipate existing scenarios which may be mixing in classical mappings into existing declarative hierarchies, an error is now raised if multiple mapped bases are detected for a given class.

  References: #4321

### sql

- [sql] [bug]

  Fixed issue that is closely related to #3639 where an expression rendered in a boolean context on a non-native boolean backend would be compared to 1/0 even though it is already an implicitly boolean expression, when `ColumnElement.self_group()` were used. While this does not affect the user-friendly backends (MySQL, SQLite) it was not handled by Oracle (and possibly SQL Server). Whether or not the expression is implicitly boolean on any database is now determined up front as an additional check to not generate the integer comparison within the compilation of the statement.

  References: #4320

- [sql] [bug]

  Added missing window function parameters `WithinGroup.over.range_` and `WithinGroup.over.rows` parameters to the `WithinGroup.over()` and `FunctionFilter.over()` methods, to correspond to the range/rows feature added to the “over” method of SQL functions as part of #3049 in version 1.1.

  References: #4322

- [sql] [bug]

  Fixed bug where the multi-table support for UPDATE and DELETE statements did not consider the additional FROM elements as targets for correlation, when a correlated SELECT were also combined with the statement. This change now includes that a SELECT statement in the WHERE clause for such a statement will try to auto-correlate back to these additional tables in the parent UPDATE/DELETE or unconditionally correlate if `Select.correlate()` is used. Note that auto-correlation raises an error if the SELECT statement would have no FROM clauses as a result, which can now occur if the parent UPDATE/DELETE specifies the same tables in its additional set of tables; specify `Select.correlate()` explicitly to resolve.

  References: #4313

### oracle

- [oracle] [bug]

  For cx_Oracle, Integer datatypes will now be bound to “int”, per advice from the cx_Oracle developers. Previously, using cx_Oracle.NUMBER caused a loss in precision within the cx_Oracle 6.x series.

  References: #4309

### misc

- [bug] [py3k]

  Started importing “collections” from “collections.abc” under Python 3.3 and greater for Python 3.8 compatibility. Pull request courtesy Nathaniel Knight.

- [no_tags]

  Fixed issue where the “schema” name used for a SQLite database within table reflection would not quote the schema name correctly. Pull request courtesy Phillip Cloud.

## 1.2.10

Released: July 13, 2018

### orm

- [orm] [bug]

  Fixed bug in `Bundle` construct where placing two columns of the same name would be de-duplicated, when the `Bundle` were used as part of the rendered SQL, such as in the ORDER BY or GROUP BY of the statement.

  References: #4295

- [orm] [bug]

  Fixed regression in 1.2.9 due to #4287 where using a `Load` option in conjunction with a string wildcard would result in a TypeError.

  References: #4298

### sql

- [sql] [bug]

  Fixed bug where a `Sequence` would be dropped explicitly before any `Table` that refers to it, which breaks in the case when the sequence is also involved in a server-side default for that table, when using `MetaData.drop_all()`. The step which processes sequences to be dropped via non server-side column default functions is now invoked after the table itself is dropped.

  References: #4300

## 1.2.9

Released: June 29, 2018

### orm

- [orm] [bug]

  Fixed issue where chaining multiple join elements inside of `Query.join()` might not correctly adapt to the previous left-hand side, when chaining joined inheritance classes that share the same base class.

  References: #3505

- [orm] [bug]

  Fixed bug in cache key generation for baked queries which could cause a too-short cache key to be generated for the case of eager loads across subclasses. This could in turn cause the eagerload query to be cached in place of a non-eagerload query, or vice versa, for a polymorphic “selectin” load, or possibly for lazy loads or selectin loads as well.

  References: #4287

- [orm] [bug]

  Fixed bug in new polymorphic selectin loading where the BakedQuery used internally would be mutated by the given loader options, which would both inappropriately mutate the subclass query as well as carry over the effect to subsequent queries.

  References: #4286

- [orm] [bug]

  Fixed regression caused by #4256 (itself a regression fix for #4228) which breaks an undocumented behavior which converted for a non-sequence of entities passed directly to the `Query` constructor into a single-element sequence. While this behavior was never supported or documented, it’s already in use so has been added as a behavioral contract to `Query`.

  References: #4269

- [orm] [bug]

  Fixed an issue that was both a performance regression in 1.2 as well as an incorrect result regarding the “baked” lazy loader, involving the generation of cache keys from the original `Query` object’s loader options. If the loader options were built up in a “branched” style using common base elements for multiple options, the same options would be rendered into the cache key repeatedly, causing both a performance issue as well as generating the wrong cache key. This is fixed, along with a performance improvement when such “branched” options are applied via `Query.options()` to prevent the same option objects from being applied repeatedly.

  References: #4270

### sql

- [sql] [bug]

  Fixed regression in 1.2 due to #4147 where a `Table` that has had some of its indexed columns redefined with new ones, as would occur when overriding columns during reflection or when using `Table.extend_existing`, such that the `Table.tometadata()` method would fail when attempting to copy those indexes as they still referred to the replaced column. The copy logic now accommodates for this condition.

  References: #4279

### mysql

- [mysql] [bug]

  Fixed percent-sign doubling in mysql-connector-python dialect, which does not require de-doubling of percent signs. Additionally, the mysql- connector-python driver is inconsistent in how it passes the column names in cursor.description, so a workaround decoder has been added to conditionally decode these randomly-sometimes-bytes values to unicode only if needed. Also improved test support for mysql-connector-python, however it should be noted that this driver still has issues with unicode that continue to be unresolved as of yet.

- [mysql] [bug]

  Fixed bug in index reflection where on MySQL 8.0 an index that includes ASC or DESC in an indexed column specification would not be correctly reflected, as MySQL 8.0 introduces support for returning this information in a table definition string.

  References: #4293

- [mysql] [bug]

  Fixed bug in MySQLdb dialect and variants such as PyMySQL where an additional “unicode returns” check upon connection makes explicit use of the “utf8” character set, which in MySQL 8.0 emits a warning that utf8mb4 should be used. This is now replaced with a utf8mb4 equivalent. Documentation is also updated for the MySQL dialect to specify utf8mb4 in all examples. Additional changes have been made to the test suite to use utf8mb3 charsets and databases (there seem to be collation issues in some edge cases with utf8mb4), and to support configuration default changes made in MySQL 8.0 such as explicit_defaults_for_timestamp as well as new errors raised for invalid MyISAM indexes.

  References: #4283

- [mysql] [bug]

  The `Update` construct now accommodates a `Join` object as supported by MySQL for UPDATE..FROM. As the construct already accepted an alias object for a similar purpose, the feature of UPDATE against a non-table was already implied so this has been added.

  References: #3645

### sqlite

- [sqlite] [bug]

  Fixed issue in test suite where SQLite 3.24 added a new reserved word that conflicted with a usage in TypeReflectionTest. Pull request courtesy Nils Philippsen.

### mssql

- [mssql] [bug]

  Fixed bug in MSSQL reflection where when two same-named tables in different schemas had same-named primary key constraints, foreign key constraints referring to one of the tables would have their columns doubled, causing errors. Pull request courtesy Sean Dunn.

  References: #4288

- [mssql] [bug] [py3k]

  Fixed issue within the SQL Server dialect under Python 3 where when running against a non-standard SQL server database that does not contain either the “sys.dm_exec_sessions” or “sys.dm_pdw_nodes_exec_sessions” views, leading to a failure to fetch the isolation level, the error raise would fail due to an UnboundLocalError.

  References: #4273

### oracle

- [oracle] [feature]

  Added a new event currently used only by the cx_Oracle dialect, `DialectEvents.setiputsizes()`. The event passes a dictionary of `BindParameter` objects to DBAPI-specific type objects that will be passed, after conversion to parameter names, to the cx_Oracle `cursor.setinputsizes()` method. This allows both visibility into the setinputsizes process as well as the ability to alter the behavior of what datatypes are passed to this method.

  See also

  Fine grained control over cx_Oracle data binding performance with setinputsizes

  References: #4290

- [oracle] [bug] [mysql]

  Fixed INSERT FROM SELECT with CTEs for the Oracle and MySQL dialects, where the CTE was being placed above the entire statement as is typical with other databases, however Oracle and MariaDB 10.2 wants the CTE underneath the “INSERT” segment. Note that the Oracle and MySQL dialects don’t yet work when a CTE is applied to a subquery inside of an UPDATE or DELETE statement, as the CTE is still applied to the top rather than inside the subquery.

  References: #4275

### misc

- [feature] [ext]

  Added new attribute `Query.lazy_loaded_from` which is populated with an `InstanceState` that is using this `Query` in order to lazy load a relationship. The rationale for this is that it serves as a hint for the horizontal sharding feature to use, such that the identity token of the state can be used as the default identity token to use for the query within id_chooser().

  References: #4243

- [bug] [py3k]

  Replaced the usage of inspect.formatargspec() with a vendored version copied from the Python standard library, as inspect.formatargspec() is deprecated and as of Python 3.7.0 is emitting a warning.

  References: #4291

## 1.2.8

Released: May 28, 2018

### orm

- [orm] [bug]

  Fixed regression in 1.2.7 caused by #4228, which itself was fixing a 1.2-level regression, where the `query_cls` callable passed to a `Session` was assumed to be a subclass of `Query` with class method availability, as opposed to an arbitrary callable. In particular, the dogpile caching example illustrates `query_cls` as a function and not a `Query` subclass.

  References: #4256

- [orm] [bug]

  Fixed a long-standing regression that occurred in version 1.0, which prevented the use of a custom `MapperOption` that alters the _params of a `Query` object for a lazy load, since the lazy loader itself would overwrite those parameters. This applies to the “temporal range” example on the wiki. Note however that the `Query.populate_existing()` method is now required in order to rewrite the mapper options associated with an object already loaded in the identity map.

  As part of this change, a custom defined `MapperOption` will now cause lazy loaders related to the target object to use a non-baked query by default unless the `MapperOption._generate_cache_key()` method is implemented. In particular, this repairs one regression which occurred when using the dogpile.cache “advanced” example, which was not returning cached results and instead emitting SQL due to an incompatibility with the baked query loader; with the change, the `RelationshipCache` option included for many releases in the dogpile example will disable the “baked” query altogether. Note that the dogpile example is also modernized to avoid both of these issues as part of issue #4258.

  References: #4128

- [orm] [bug]

  Fixed bug where the new `Result.with_post_criteria()` method would not interact with a subquery-eager loader correctly, in that the “post criteria” would not be applied to embedded subquery eager loaders. This is related to #4128 in that the post criteria feature is now used by the lazy loader.

- [orm] [bug]

  Updated the dogpile.caching example to include new structures that accommodate for the “baked” query system, which is used by default within lazy loaders and some eager relationship loaders. The dogpile.caching “relationship_caching” and “advanced” examples were also broken due to #4256. The issue here is also worked-around by the fix in #4128.

  References: #4258

### engine

- [engine] [bug]

  Fixed connection pool issue whereby if a disconnection error were raised during the connection pool’s “reset on return” sequence in conjunction with an explicit transaction opened against the enclosing `Connection` object (such as from calling `Session.close()` without a rollback or commit, or calling `Connection.close()` without first closing a transaction declared with `Connection.begin()`), a double-checkin would result, which could then lead towards concurrent checkouts of the same connection. The double-checkin condition is now prevented overall by an assertion, as well as the specific double-checkin scenario has been fixed.

  References: #4252

- [engine] [bug]

  Fixed a reference leak issue where the values of the parameter dictionary used in a statement execution would remain referenced by the “compiled cache”, as a result of storing the key view used by Python 3 dictionary keys(). Pull request courtesy Olivier Grisel.

### sql

- [sql] [bug]

  Fixed issue where the “ambiguous literal” error message used when interpreting literal values as SQL expression values would encounter a tuple value, and fail to format the message properly. Pull request courtesy Miguel Ventura.

### mssql

- [mssql] [bug]

  Fixed a 1.2 regression caused by #4061 where the SQL Server “BIT” type would be considered to be “native boolean”. The goal here was to avoid creating a CHECK constraint on the column, however the bigger issue is that the BIT value does not behave like a true/false constant and cannot be interpreted as a standalone expression, e.g. “WHERE <column>”. The SQL Server dialect now goes back to being non-native boolean, but with an extra flag that still avoids creating the CHECK constraint.

  References: #4250

### oracle

- [oracle] [bug]

  The Oracle BINARY_FLOAT and BINARY_DOUBLE datatypes now participate within cx_Oracle.setinputsizes(), passing along NATIVE_FLOAT, so as to support the NaN value. Additionally, `BINARY_FLOAT`, `BINARY_DOUBLE` and `DOUBLE_PRECISION` now subclass `Float`, since these are floating point datatypes, not decimal. These datatypes were already defaulting the `Float.asdecimal` flag to False in line with what `Float` already does.

  References: #4264

- [oracle] [bug]

  Added reflection capabilities for the `BINARY_FLOAT`, `BINARY_DOUBLE` datatypes.

- [oracle] [bug]

  Altered the Oracle dialect such that when an `Integer` type is in use, the cx_Oracle.NUMERIC type is set up for setinputsizes(). In SQLAlchemy 1.1 and earlier, cx_Oracle.NUMERIC was passed for all numeric types unconditionally, and in 1.2 this was removed to allow for better numeric precision. However, for integers, some database/client setups will fail to coerce boolean values True/False into integers which introduces regressive behavior when using SQLAlchemy 1.2. Overall, the setinputsizes logic seems like it will need a lot more flexibility going forward so this is a start for that.

  References: #4259

### tests

- [tests] [bug]

  Fixed a bug in the test suite where if an external dialect returned `None` for `server_version_info`, the exclusion logic would raise an `AttributeError`.

  References: #4249

### misc

- [bug] [ext]

  The horizontal sharding extension now makes use of the identity token added to ORM identity keys as part of #4137, when an object refresh or column-based deferred load or unexpiration operation occurs. Since we know the “shard” that the object originated from, we make use of this value when refreshing, thereby avoiding queries against other shards that don’t match this object’s identity in any case.

  References: #4247

- [bug] [ext]

  Fixed a race condition which could occur if automap `AutomapBase.prepare()` were used within a multi-threaded context against other threads which may call `configure_mappers()` as a result of use of other mappers. The unfinished mapping work of automap is particularly sensitive to being pulled in by a `configure_mappers()` step leading to errors.

  References: #4266

## 1.2.7

Released: April 20, 2018

### orm

- [orm] [bug]

  Fixed regression in 1.2 within sharded query feature where the new “identity_token” element was not being correctly considered within the scope of a lazy load operation, when searching the identity map for a related many-to-one element. The new behavior will allow for making use of the “id_chooser” in order to determine the best identity key to retrieve from the identity map. In order to achieve this, some refactoring of 1.2’s “identity_token” approach has made some slight changes to the implementation of `ShardedQuery` which should be noted for other derivations of this class.

  References: #4228

- [orm] [bug]

  Fixed issue in single-inheritance loading where the use of an aliased entity against a single-inheritance subclass in conjunction with the `Query.select_from()` method would cause the SQL to be rendered with the unaliased table mixed in to the query, causing a cartesian product. In particular this was affecting the new “selectin” loader when used against a single-inheritance subclass.

  References: #4241

### sql

- [sql] [bug]

  Fixed issue where the compilation of an INSERT statement with the “literal_binds” option that also uses an explicit sequence and “inline” generation, as on PostgreSQL and Oracle, would fail to accommodate the extra keyword argument within the sequence processing routine.

  References: #4231

### postgresql

- [postgresql] [feature]

  Added new PG type `REGCLASS` which assists in casting table names to OID values. Pull request courtesy Sebastian Bank.

  References: #4160

- [postgresql] [bug]

  Fixed bug where the special “not equals” operator for the PostgreSQL “range” datatypes such as DATERANGE would fail to render “IS NOT NULL” when compared to the Python `None` value.

  References: #4229

### mssql

- [mssql] [bug]

  Fixed 1.2 regression caused by #4060 where the query used to reflect SQL Server cross-schema foreign keys was limiting the criteria incorrectly.

  References: #4234

### oracle

- [oracle] [bug]

  The Oracle NUMBER datatype is reflected as INTEGER if the precision is NULL and the scale is zero, as this is how INTEGER values come back when reflected from Oracle’s tables. Pull request courtesy Kent Bower.

## 1.2.6

Released: March 30, 2018

### orm

- [orm] [bug]

  Fixed bug where using `Mutable.associate_with()` or `Mutable.as_mutable()` in conjunction with a class that has non- primary mappers set up with alternatively-named attributes would produce an attribute error. Since non-primary mappers are not used for persistence, the mutable extension now excludes non-primary mappers from its instrumentation steps.

  References: #4215

### engine

- [engine] [bug]

  Fixed bug in connection pool where a connection could be present in the pool without all of its “connect” event handlers called, if a previous “connect” handler threw an exception; note that the dialects themselves have connect handlers that emit SQL, such as those which set transaction isolation, which can fail if the database is in a non-available state, but still allows a connection. The connection is now invalidated first if any of the connect handlers fail.

  References: #4225

### sql

- [sql] [bug]

  Fixed a regression that occurred from the previous fix to #4204 in version 1.2.5, where a CTE that refers to itself after the `CTE.alias()` method has been called would not refer to itself correctly.

  References: #4204

### postgresql

- [postgresql] [feature]

  Added support for “PARTITION BY” in PostgreSQL table definitions, using “postgresql_partition_by”. Pull request courtesy Vsevolod Solovyov.

### mssql

- [mssql] [bug]

  Adjusted the SQL Server version detection for pyodbc to only allow for numeric tokens, filtering out non-integers, since the dialect does tuple- numeric comparisons with this value. This is normally true for all known SQL Server / pyodbc drivers in any case.

  References: #4227

### oracle

- [oracle] [bug]

  The minimum cx_Oracle version supported is 5.2 (June 2015). Previously, the dialect asserted against version 5.0 but as of 1.2.2 we are using some symbols that did not appear until 5.2.

  References: #4211

### misc

- [bug] [declarative]

  Removed a warning that would be emitted when calling upon `__table_args__`, `__mapper_args__` as named with a `@declared_attr` method, when called from a non-mapped declarative mixin. Calling these directly is documented as the approach to use when one is overriding one of these methods on a mapped class. The warning still emits for regular attribute names.

  References: #4221

## 1.2.5

Released: March 6, 2018

### orm

- [orm] [feature]

  Added new feature `Query.only_return_tuples()`. Causes the `Query` object to return keyed tuple objects unconditionally even if the query is against a single entity. Pull request courtesy Eric Atkin.

- [orm] [bug]

  Fixed bug in new “polymorphic selectin” loading when a selection of polymorphic objects were to be partially loaded from a relationship lazy loader, leading to an “empty IN” condition within the load that raises an error for the “inline” form of “IN”.

  References: #4199

- [orm] [bug]

  Fixed 1.2 regression where a mapper option that contains an `AliasedClass` object, as is typical when using the `QueryableAttribute.of_type()` method, could not be pickled. 1.1’s behavior was to omit the aliased class objects from the path, so this behavior is restored.

  References: #4209

### sql

- [sql] [bug]

  Fixed bug in :class:.`CTE` construct along the same lines as that of #4204 where a `CTE` that was aliased would not copy itself correctly during a “clone” operation as is frequent within the ORM as well as when using the `ClauseElement.params()` method.

  References: #4210

- [sql] [bug]

  Fixed bug in CTE rendering where a `CTE` that was also turned into an `Alias` would not render its “ctename AS aliasname” clause appropriately if there were more than one reference to the CTE in a FROM clause.

  References: #4204

- [sql] [bug]

  Fixed bug in new “expanding IN parameter” feature where the bind parameter processors for values wasn’t working at all, tests failed to cover this pretty basic case which includes that ENUM values weren’t working.

  References: #4198

### postgresql

- [postgresql] [bug] [py3k]

  Fixed bug in PostgreSQL COLLATE / ARRAY adjustment first introduced in #4006 where new behaviors in Python 3.7 regular expressions caused the fix to fail.

  This change is also backported to: 1.1.18

  References: #4208

### mysql

- [mysql] [bug]

  MySQL dialects now query the server version using `SELECT @@version` explicitly to the server to ensure we are getting the correct version information back. Proxy servers like MaxScale interfere with the value that is passed to the DBAPI’s connection.server_version value so this is no longer reliable.

  This change is also backported to: 1.1.18

  References: #4205

## 1.2.4

Released: February 22, 2018

### orm

- [orm] [bug]

  Fixed 1.2 regression in ORM versioning feature where a mapping against a `select()` or `alias()` that also used a versioning column against the underlying table would fail due to the check added as part of #3673.

  References: #4193

### engine

- [engine] [bug]

  Fixed regression caused in 1.2.3 due to fix from #4181 where the changes to the event system involving `Engine` and `OptionEngine` did not accommodate for event removals, which would raise an `AttributeError` when invoked at the class level.

  References: #4190

### sql

- [sql] [bug]

  Fixed bug where CTE expressions would not have their name or alias name quoted when the given name is case sensitive or otherwise requires quoting. Pull request courtesy Eric Atkin.

  References: #4197

## 1.2.3

Released: February 16, 2018

### orm

- [orm] [feature]

  Added new argument `set_attribute.initiator` to the `set_attribute()` function, allowing an event token received from a listener function to be propagated to subsequent set events.

- [orm] [bug]

  Fixed issue in post_update feature where an UPDATE is emitted when the parent object has been deleted but the dependent object is not. This issue has existed for a long time however since 1.2 now asserts rows matched for post_update, this was raising an error.

  This change is also backported to: 1.1.16

  References: #4187

- [orm] [bug]

  Fixed regression caused by fix for issue #4116 affecting versions 1.2.2 as well as 1.1.15, which had the effect of mis-calculation of the “owning class” of an `AssociationProxy` as the `NoneType` class in some declarative mixin/inheritance situations as well as if the association proxy were accessed off of an un-mapped class. The “figure out the owner” logic has been replaced by an in-depth routine that searches through the complete mapper hierarchy assigned to the class or subclass to determine the correct (we hope) match; will not assign the owner if no match is found. An exception is now raised if the proxy is used against an un-mapped instance.

  This change is also backported to: 1.1.16

  References: #4185

- [orm] [bug]

  Fixed bug where the `Bundle` object did not correctly report upon the primary `Mapper` object represented by the bundle, if any. An immediate side effect of this issue was that the new selectinload loader strategy wouldn’t work with the horizontal sharding extension.

  References: #4175

- [orm] [bug]

  Fixed bug in concrete inheritance mapping where user-defined attributes such as hybrid properties that mirror the names of mapped attributes from sibling classes would be overwritten by the mapper as non-accessible at the instance level. Additionally ensured that user-bound descriptors are not implicitly invoked at the class level during the mapper configuration stage.

  References: #4188

- [orm] [bug]

  Fixed bug where the `reconstructor()` event helper would not be recognized if it were applied to the `__init__()` method of the mapped class.

  References: #4178

### engine

- [engine] [bug]

  Fixed bug where events associated with an `Engine` at the class level would be doubled when the `Engine.execution_options()` method were used. To achieve this, the semi-private class `OptionEngine` no longer accepts events directly at the class level and will raise an error; the class only propagates class-level events from its parent `Engine`. Instance-level events continue to work as before.

  References: #4181

- [engine] [bug]

  The `URL` object now allows query keys to be specified multiple times where their values will be joined into a list. This is to support the plugins feature documented at `CreateEnginePlugin` which documents that “plugin” can be passed multiple times. Additionally, the plugin names can be passed to `create_engine()` outside of the URL using the new `create_engine.plugins` parameter.

  References: #4170

### sql

- [sql] [feature]

  Added support for `Enum` to persist the values of the enumeration, rather than the keys, when using a Python pep-435 style enumerated object. The user supplies a callable function that will return the string values to be persisted. This allows enumerations against non-string values to be value-persistable as well. Pull request courtesy Jon Snyder.

  References: #3906

- [sql] [bug]

  Fixed bug where the `Enum` type wouldn’t handle enum “aliases” correctly, when more than one key refers to the same value. Pull request courtesy Daniel Knell.

  References: #4180

### postgresql

- [postgresql] [bug]

  Added “SSL SYSCALL error: Operation timed out” to the list of messages that trigger a “disconnect” scenario for the psycopg2 driver. Pull request courtesy André Cruz.

  This change is also backported to: 1.1.16

- [postgresql] [bug]

  Added “TRUNCATE” to the list of keywords accepted by the PostgreSQL dialect as an “autocommit”-triggering keyword. Pull request courtesy Jacob Hayes.

  This change is also backported to: 1.1.16

### sqlite

- [sqlite] [bug]

  Fixed the import error raised when a platform has neither pysqlite2 nor sqlite3 installed, such that the sqlite3-related import error is raised, not the pysqlite2 one which is not the actual failure mode. Pull request courtesy Robin.

### oracle

- [oracle] [feature]

  The ON DELETE options for foreign keys are now part of Oracle reflection. Oracle does not support ON UPDATE cascades. Pull request courtesy Miroslav Shubernetskiy.

- [oracle] [bug]

  Fixed bug in cx_Oracle disconnect detection, used by pre_ping and other features, where an error could be raised as DatabaseError which includes a numeric error code; previously we weren’t checking in this case for a disconnect code.

  References: #4182

### tests

- [tests] [bug]

  A test added in 1.2 thought to confirm a Python 2.7 behavior turns out to be confirming the behavior only as of Python 2.7.8. Python bug #8743 still impacts set comparison in Python 2.7.7 and earlier, so the test in question involving AssociationSet no longer runs for these older Python 2.7 versions.

  References: #3265

### misc

- [bug] [pool]

  Fixed a fairly serious connection pool bug where a connection that is acquired after being refreshed as a result of a user-defined `DisconnectionError` or due to the 1.2-released “pre_ping” feature would not be correctly reset if the connection were returned to the pool by weakref cleanup (e.g. the front-facing object is garbage collected); the weakref would still refer to the previously invalidated DBAPI connection which would have the reset operation erroneously called upon it instead. This would lead to stack traces in the logs and a connection being checked into the pool without being reset, which can cause locking issues.

  This change is also backported to: 1.1.16

  References: #4184

## 1.2.2

Released: January 24, 2018

### orm

- [orm] [bug]

  Fixed 1.2 regression regarding new bulk_replace event where a backref would fail to remove an object from the previous owner when a bulk-assignment assigned the object to a new owner.

  References: #4171

### mysql

- [mysql] [bug]

  Added more MySQL 8.0 reserved words to the MySQL dialect for quoting purposes. Pull request courtesy Riccardo Magliocchetti.

### mssql

- [mssql] [bug]

  Added ODBC error code 10054 to the list of error codes that count as a disconnect for ODBC / MSSQL server.

  References: #4164

### oracle

- [oracle] [bug]

  The cx_Oracle dialect now calls setinputsizes() with cx_Oracle.NCHAR unconditionally when the NVARCHAR2 datatype, in SQLAlchemy corresponding to sqltypes.Unicode(), is in use. Per cx_Oracle’s author this allows the correct conversions to occur within the Oracle client regardless of the setting for NLS_NCHAR_CHARACTERSET.

  References: #4163

## 1.2.1

Released: January 15, 2018

### orm

- [orm] [bug]

  Fixed bug where an object that is expunged during a rollback of a nested or subtransaction which also had its primary key mutated would not be correctly removed from the session, causing subsequent issues in using the session.

  This change is also backported to: 1.1.16

  References: #4151

- [orm] [bug]

  Fixed regression where pickle format of a Load / _UnboundLoad object (e.g. loader options) changed and `__setstate__()` was raising an UnboundLocalError for an object received from the legacy format, even though an attempt was made to do so. tests are now added to ensure this works.

  References: #4159

- [orm] [bug]

  Fixed regression caused by new lazyload caching scheme in #3954 where a query that makes use of loader options with of_type would cause lazy loads of unrelated paths to fail with a TypeError.

  References: #4153

- [orm] [bug]

  Fixed bug in new “selectin” relationship loader where the loader could try to load a non-existent relationship when loading a collection of polymorphic objects, where only some of the mappers include that relationship, typically when `PropComparator.of_type()` is being used.

  References: #4156

### sql

- [sql] [bug]

  Fixed bug in `Insert.values()` where using the “multi-values” format in combination with `Column` objects as keys rather than strings would fail. Pull request courtesy Aubrey Stark-Toller.

  This change is also backported to: 1.1.16

  References: #4162

### mssql

- [mssql] [bug]

  Fixed regression in 1.2 where newly repaired quoting of collation names in #3785 breaks SQL Server, which explicitly does not understand a quoted collation name. Whether or not mixed-case collation names are quoted or not is now deferred down to a dialect-level decision so that each dialect can prepare these identifiers directly.

  References: #4154

### oracle

- [oracle] [bug]

  Fixed regression where the removal of most setinputsizes rules from cx_Oracle dialect impacted the TIMESTAMP datatype’s ability to retrieve fractional seconds.

  References: #4157

- [oracle] [bug]

  Fixed regression in Oracle imports where a missing comma caused an undefined symbol to be present. Pull request courtesy Miroslav Shubernetskiy.

### tests

- [tests] [bug]

  Removed an oracle-specific requirements rule from the public test suite that was interfering with third party dialect suites.

- [tests] [bug]

  Added a new exclusion rule group_by_complex_expression which disables tests that use “GROUP BY <expr>”, which seems to be not viable for at least two third party dialects.

### misc

- [bug] [ext]

  Fixed regression in association proxy due to #3769 (allow for chained any() / has()) where contains() against an association proxy chained in the form (o2m relationship, associationproxy(m2o relationship, m2o relationship)) would raise an error regarding the re-application of contains() on the final link of the chain.

  References: #4150

## 1.2.0

Released: December 27, 2017

### orm

- [orm] [feature]

  Added a new data member to the identity key tuple used by the ORM’s identity map, known as the “identity_token”. This token defaults to None but may be used by database sharding schemes to differentiate objects in memory with the same primary key that come from different databases. The horizontal sharding extension integrates this token applying the shard identifier to it, thus allowing primary keys to be duplicated across horizontally sharded backends.

  See also

  Identity key enhancements to support sharding

  References: #4137

- [orm] [bug] [ext]

  Fixed bug where the association proxy would inadvertently link itself to an `AliasedClass` object if it were called first with the `AliasedClass` as a parent, causing errors upon subsequent usage.

  This change is also backported to: 1.1.15

  References: #4116

- [orm] [bug]

  Fixed bug in `contains_eager()` query option where making use of a path that used `PropComparator.of_type()` to refer to a subclass across more than one level of joins would also require that the “alias” argument were provided with the same subtype in order to avoid adding unwanted FROM clauses to the query; additionally, using `contains_eager()` across subclasses that use `aliased()` objects of subclasses as the `PropComparator.of_type()` argument will also render correctly.

  References: #4130

- [orm] [bug]

  The `Query.exists()` method will now disable eager loaders for when the query is rendered. Previously, joined-eager load joins would be rendered unnecessarily as well as subquery eager load queries would be needlessly generated. The new behavior matches that of the `Query.subquery()` method.

  References: #4032

### orm declarative

- [orm] [declarative] [bug]

  Fixed a bug where a descriptor, which is a mapped column or a relationship elsewhere in a hierarchy based on `AbstractConcreteBase`, would be referenced during a refresh operation, leading to an error since the attribute is not mapped as a mapper property. A similar issue can arise for other attributes like the “type” column added by `AbstractConcreteBase` if the class fails to include “concrete=True” in its mapper, however the check here should also prevent that scenario from causing a problem.

  This change is also backported to: 1.1.15

  References: #4124

### engine

- [engine] [feature]

  The “password” attribute of the `URL` object can now be any user-defined or user-subclassed string object that responds to the Python `str()` builtin. The object passed will be maintained as the datamember `URL.password_original` and will be consulted when the `URL.password` attribute is read to produce the string value.

  References: #4089

### sql

- [sql] [bug]

  Fixed bug where `__repr__` of `ColumnDefault` would fail if the argument were a tuple. Pull request courtesy Nicolas Caniart.

  This change is also backported to: 1.1.15

  References: #4126

- [sql] [bug]

  Reworked the new “autoescape” feature introduced in New “autoescape” option for startswith(), endswith() in 1.2.0b2 to be fully automatic; the escape character now defaults to a forwards slash `"/"` and is applied to percent, underscore, as well as the escape character itself, for fully automatic escaping. The character can also be changed using the “escape” parameter.

  See also

  New “autoescape” option for startswith(), endswith()

  References: #2694

- [sql] [bug]

  Fixed bug where the `Table.tometadata()` method would not properly accommodate `Index` objects that didn’t consist of simple column expressions, such as indexes against a `text()` construct, indexes that used SQL expressions or `func`, etc. The routine now copies expressions fully to a new `Index` object while substituting all table-bound `Column` objects for those of the target table.

  References: #4147

- [sql] [bug]

  Changed the “visit name” of `ColumnElement` from “column” to “column_element”, so that when this element is used as the basis for a user-defined SQL element, it is not assumed to behave like a table-bound `ColumnClause` when processed by various SQL traversal utilities, as are commonly used by the ORM.

  References: #4142

- [sql] [bug] [ext]

  Fixed issue in `ARRAY` datatype which is essentially the same issue as that of #3832, except not a regression, where column attachment events on top of `ARRAY` would not fire correctly, thus interfering with systems which rely upon this. A key use case that was broken by this is the use of mixins to declare columns that make use of `MutableList.as_mutable()`.

  References: #4141

- [sql] [bug]

  Fixed bug in new “expanding bind parameter” feature whereby if multiple params were used in one statement, the regular expression would not match the parameter name correctly.

  References: #4140

- [sql] [enhancement]

  Implemented “DELETE..FROM” syntax for PostgreSQL, MySQL, MS SQL Server (as well as within the unsupported Sybase dialect) in a manner similar to how “UPDATE..FROM” works. A DELETE statement that refers to more than one table will switch into “multi-table” mode and render the appropriate “USING” or multi-table “FROM” clause as understood by the database. Pull request courtesy Pieter Mulder.

  See also

  Multiple-table criteria support for DELETE

  References: #959

### postgresql

- [postgresql] [feature]

  Added new `MONEY` datatype. Pull request courtesy Cleber J Santos.

### mysql

- [mysql] [bug]

  MySQL 5.7.20 now warns for use of the @tx_isolation variable; a version check is now performed and uses @transaction_isolation instead to prevent this warning.

  This change is also backported to: 1.1.15

  References: #4120

- [mysql] [bug]

  Fixed regression from issue 1.2.0b3 where “MariaDB” version comparison can fail for some particular MariaDB version strings under Python 3.

  References: #4115

### mssql

- [mssql] [bug]

  Fixed bug where sqltypes.BINARY and sqltypes.VARBINARY datatypes would not include correct bound-value handlers for pyodbc, which allows the pyodbc.NullParam value to be passed that helps with FreeTDS.

  References: #4121

### oracle

- [oracle] [bug]

  Added some additional rules to fully handle `Decimal('Infinity')`, `Decimal('-Infinity')` values with cx_Oracle numerics when using `asdecimal=True`.

  References: #4064

### misc

- [misc] [feature]

  Added a new errors section to the documentation with background about common error messages. Selected exceptions within SQLAlchemy will include a link in their string output to the relevant section within this page.

- [enhancement] [ext]

  Added new method `Result.with_post_criteria()` to baked query system, allowing non-SQL-modifying transformations to take place after the query has been pulled from the cache. Among other things, this method can be used with `ShardedQuery` to set the shard identifier. `ShardedQuery` has also been modified such that its `ShardedQuery.get()` method interacts correctly with that of `Result`.

  References: #4135

## 1.2.0b3

Released: October 13, 2017

### orm

- [orm] [bug]

  Fixed bug where ORM relationship would warn against conflicting sync targets (e.g. two relationships would both write to the same column) for sibling classes in an inheritance hierarchy, where the two relationships would never actually conflict during writes.

  This change is also backported to: 1.1.15

  References: #4078

- [orm] [bug]

  Fixed bug where correlated select used against single-table inheritance entity would fail to render correctly in the outer query, due to adjustment for single inheritance discriminator criteria inappropriately re-applying the criteria to the outer query.

  This change is also backported to: 1.1.15

  References: #4103

- [orm] [bug]

  Fixed bug in `Session.merge()` following along similar lines as that of #4030, where an internal check for a target object in the identity map could lead to an error if it were to be garbage collected immediately before the merge routine actually retrieves the object.

  This change is also backported to: 1.1.14

  References: #4069

- [orm] [bug]

  Fixed bug where an `undefer_group()` option would not be recognized if it extended from a relationship that was loading using joined eager loading. Additionally, as the bug led to excess work being performed, Python function call counts are also improved by 20% within the initial calculation of result set columns, complementing the joined eager load improvements of #3915.

  This change is also backported to: 1.1.14

  References: #4048

- [orm] [bug]

  Fixed bug in `Session.merge()` where objects in a collection that had the primary key attribute set to `None` for a key that is typically autoincrementing would be considered to be a database-persisted key for part of the internal deduplication process, causing only one object to actually be inserted in the database.

  This change is also backported to: 1.1.14

  References: #4056

- [orm] [bug]

  An `InvalidRequestError` is raised when a `synonym()` is used against an attribute that is not against a `MapperProperty`, such as an association proxy. Previously, a recursion overflow would occur trying to locate non-existent attributes.

  This change is also backported to: 1.1.14

  References: #4067

- [orm] [bug]

  Fixed regression introduced in 1.2.0b1 due to #3934 where the `Session` would fail to “deactivate” the transaction, if a rollback failed (the target issue is when MySQL loses track of a SAVEPOINT). This would cause a subsequent call to `Session.rollback()` to raise an error a second time, rather than completing and bringing the `Session` back to ACTIVE.

  References: #4050

- [orm] [bug]

  Fixed issue where the `make_transient_to_detached()` function would expire all attributes on the target object, including “deferred” attributes, which has the effect of the attribute being undeferred for the next refresh, causing an unexpected load of the attribute.

  References: #4084

- [orm] [bug]

  Fixed bug involving delete-orphan cascade where a related item that becomes an orphan before the parent object is part of a session is still tracked as moving into orphan status, which results in it being expunged from the session rather than being flushed.

  Note

  This fix was inadvertently merged during the 1.2.0b3 release and was not added to the changelog at that time. This changelog note was added to the release retroactively as of version 1.2.13.

  References: #4040

- [orm] [bug]

  Fixed bug in “selectin” polymorphic loading, loads subclasses using separate IN queries which prevented “selectin” and “inline” settings in a multi-level class hierarchy from interacting together as expected.

  References: #4026

- [orm] [bug]

  Removed the warnings that are emitted when the LRU caches employed by the mapper as well as loader strategies reach their threshold; the purpose of this warning was at first a guard against excess cache keys being generated but became basically a check on the “creating many engines” antipattern. While this is still an antipattern, the presence of test suites which both create an engine per test as well as raise on all warnings will be an inconvenience; it should not be critical that such test suites change their architecture just for this warning (though engine-per-test suite is always better).

  References: #4071

- [orm] [bug]

  Fixed regression where the use of a `undefer_group()` option in conjunction with a lazy loaded relationship option would cause an attribute error, due to a bug in the SQL cache key generation added in 1.2 as part of #3954.

  References: #4049

- [orm] [bug]

  Modified the change made to the ORM update/delete evaluator in #3366 such that if an unmapped column expression is present in the update or delete, if the evaluator can match its name to the mapped columns of the target class, a warning is emitted, rather than raising UnevaluatableError. This is essentially the pre-1.2 behavior, and is to allow migration for applications that are currently relying upon this pattern. However, if the given attribute name cannot be matched to the columns of the mapper, the UnevaluatableError is still raised, which is what was fixed in #3366.

  References: #4073

### orm declarative

- [orm] [declarative] [bug]

  A warning is emitted if a subclass attempts to override an attribute that was declared on a superclass using `@declared_attr.cascading` that the overridden attribute will be ignored. This use case cannot be fully supported down to further subclasses without more complex development efforts, so for consistency the “cascading” is honored all the way down regardless of overriding attributes.

  References: #4091

- [orm] [declarative] [bug]

  A warning is emitted if the `@declared_attr.cascading` attribute is used with a special declarative name such as `__tablename__`, as this has no effect.

  References: #4092

### engine

- [engine] [feature]

  Added `__next__()` and `next()` methods to `ResultProxy`, so that the `next()` builtin function works on the object directly. `ResultProxy` has long had an `__iter__()` method which already allows it to respond to the `iter()` builtin. The implementation for `__iter__()` is unchanged, as performance testing has indicated that iteration using a `__next__()` method with `StopIteration` is about 20% slower in both Python 2.7 and 3.6.

  References: #4077

- [engine] [bug]

  Made some adjustments to `Pool` and `Connection` such that recovery logic is not run underneath exception catches for `pool.Empty`, `AttributeError`, since when the recovery operation itself fails, Python 3 creates a misleading stack trace referring to the `Empty` / `AttributeError` as the cause, when in fact these exception catches are part of control flow.

  References: #4028

### sql

- [sql] [bug]

  Fixed bug where the recently added `ColumnOperators.any_()` and `ColumnOperators.all_()` methods didn’t work when called as methods, as opposed to using the standalone functions `any_()` and `all_()`. Also added documentation examples for these relatively unintuitive SQL operators.

  This change is also backported to: 1.1.15

  References: #4093

- [sql] [bug]

  Added a new method `DefaultExecutionContext.get_current_parameters()` which is used within a function-based default value generator in order to retrieve the current parameters being passed to the statement. The new function differs from the `DefaultExecutionContext.current_parameters` attribute in that it also provides for optional grouping of parameters that correspond to a multi-valued “insert” construct. Previously it was not possible to identify the subset of parameters that were relevant to the function call.

  See also

  Parameter helper for multi-valued INSERT with contextual default generator

  Context-Sensitive Default Functions

  References: #4075

- [sql] [bug]

  Fixed bug in new SQL comments feature where table and column comment would not be copied when using `Table.tometadata()`.

  References: #4087

- [sql] [bug]

  In release 1.1, the `Boolean` type was broken in that boolean coercion via `bool()` would occur for backends that did not feature “native boolean”, but would not occur for native boolean backends, meaning the string `"0"` now behaved inconsistently. After a poll, a consensus was reached that non-boolean values should be raising an error, especially in the ambiguous case of string `"0"`; so the `Boolean` datatype will now raise `ValueError` if an incoming value is not within the range `None, True, False, 1, 0`.

  See also

  Boolean datatype now enforces strict True/False/None values

  References: #4102

- [sql] [bug]

  Refined the behavior of `Operators.op()` such that in all cases, if the `Operators.op.is_comparison` flag is set to True, the return type of the resulting expression will be `Boolean`, and if the flag is False, the return type of the resulting expression will be the same type as that of the left-hand expression, which is the typical default behavior of other operators. Also added a new parameter `Operators.op.return_type` as well as a helper method `Operators.bool_op()`.

  See also

  The typing behavior of custom operators has been made consistent

  References: #4063

- [sql] [bug]

  Internal refinements to the `Enum`, `Interval`, and `Boolean` types, which now extend a common mixin `Emulated` that indicates a type that provides Python-side emulation of a DB native type, switching out to the DB native type when a supporting backend is in use. The PostgreSQL `INTERVAL` type when used directly will now include the correct type coercion rules for SQL expressions that also take effect for `Interval` (such as adding a date to an interval yields a datetime).

  References: #4088

### postgresql

- [postgresql] [feature]

  Added a new flag `use_batch_mode` to the psycopg2 dialect. This flag enables the use of psycopg2’s `psycopg2.extras.execute_batch` extension when the `Engine` calls upon `cursor.executemany()`. This extension provides a critical performance increase by over an order of magnitude when running INSERT statements in batch. The flag is False by default as it is considered to be experimental for now.

  See also

  Support for Batch Mode / Fast Execution Helpers

  References: #4109

- [postgresql] [bug]

  Made further fixes to the `ARRAY` class in conjunction with COLLATE, as the fix made in #4006 failed to accommodate for a multidimensional array.

  This change is also backported to: 1.1.15

  References: #4006

- [postgresql] [bug]

  Fixed bug in `array_agg` function where passing an argument that is already of type `ARRAY`, such as a PostgreSQL `array` construct, would produce a `ValueError`, due to the function attempting to nest the arrays.

  This change is also backported to: 1.1.15

  References: #4107

- [postgresql] [bug]

  Fixed bug in PostgreSQL `Insert.on_conflict_do_update()` which would prevent the insert statement from being used as a CTE, e.g. via `Insert.cte()`, within another statement.

  This change is also backported to: 1.1.15

  References: #4074

- [postgresql] [bug]

  Fixed bug where the pg8000 driver would fail if using `MetaData.reflect()` with a schema name, since the schema name would be sent as a “quoted_name” object that’s a string subclass, which pg8000 doesn’t recognize. The quoted_name type is added to pg8000’s py_types collection on connect.

  References: #4041

- [postgresql] [bug]

  Enabled UUID support for the pg8000 driver, which supports native Python uuid round trips for this datatype. Arrays of UUID are still not supported, however.

  References: #4016

### mysql

- [mysql] [bug]

  Warning emitted when MariaDB 10.2.8 or earlier in the 10.2 series is detected as there are major issues with CHECK constraints within these versions that were resolved as of 10.2.9.

  Note that this changelog message was NOT released with SQLAlchemy 1.2.0b3 and was added retroactively.

  This change is also backported to: 1.1.15

  References: #4097

- [mysql] [bug]

  Fixed issue where CURRENT_TIMESTAMP would not reflect correctly in the MariaDB 10.2 series due to a syntax change, where the function is now represented as `current_timestamp()`.

  This change is also backported to: 1.1.15

  References: #4096

- [mysql] [bug]

  MariaDB 10.2 now supports CHECK constraints (warning: use version 10.2.9 or greater due to upstream issues noted in #4097). Reflection now takes these CHECK constraints into account when they are present in the `SHOW CREATE TABLE` output.

  This change is also backported to: 1.1.15

  References: #4098

- [mysql] [bug]

  Changed the name of the `.values` attribute of the new MySQL INSERT..ON DUPLICATE KEY UPDATE construct to `.inserted`, as `Insert` already has a method called `Insert.values()`. The `.inserted` attribute ultimately renders the MySQL `VALUES()` function.

  References: #4072

### sqlite

- [sqlite] [bug]

  Fixed bug where SQLite CHECK constraint reflection would fail if the referenced table were in a remote schema, e.g. on SQLite a remote database referred to by ATTACH.

  This change is also backported to: 1.1.15

  References: #4099

### mssql

- [mssql] [feature]

  Added a new `TIMESTAMP` datatype, that correctly acts like a binary datatype for SQL Server rather than a datetime type, as SQL Server breaks the SQL standard here. Also added `ROWVERSION`, as the “TIMESTAMP” type in SQL Server is deprecated in favor of ROWVERSION.

  References: #4086

- [mssql] [feature]

  Added support for “AUTOCOMMIT” isolation level, as established via `Connection.execution_options()`, to the PyODBC and pymssql dialects. This isolation level sets the appropriate DBAPI-specific flags on the underlying connection object.

  References: #4058

- [mssql] [bug]

  Added a full range of “connection closed” exception codes to the PyODBC dialect for SQL Server, including ‘08S01’, ‘01002’, ‘08003’, ‘08007’, ‘08S02’, ‘08001’, ‘HYT00’, ‘HY010’. Previously, only ‘08S01’ was covered.

  This change is also backported to: 1.1.15

  References: #4095

- [mssql] [bug]

  SQL Server supports what SQLAlchemy calls “native boolean” with its BIT type, as this type only accepts 0 or 1 and the DBAPIs return its value as True/False. So the SQL Server dialects now enable “native boolean” support, in that a CHECK constraint is not generated for a `Boolean` datatype. The only difference vs. other native boolean is that there are no “true” / “false” constants so “1” and “0” are still rendered here.

  References: #4061

- [mssql] [bug]

  Fixed the pymssql dialect so that percent signs in SQL text, such as used in modulus expressions or literal textual values, are not doubled up, as seems to be what pymssql expects. This is despite the fact that the pymssql DBAPI uses the “pyformat” parameter style which itself considers the percent sign to be significant.

  References: #4057

- [mssql] [bug]

  Fixed bug where the SQL Server dialect could pull columns from multiple schemas when reflecting a self-referential foreign key constraint, if multiple schemas contained a constraint of the same name against a table of the same name.

  References: #4060

- [mssql] [bug] [orm]

  Added a new class of “rowcount support” for dialects that is specific to when “RETURNING”, which on SQL Server looks like “OUTPUT inserted”, is in use, as the PyODBC backend isn’t able to give us rowcount on an UPDATE or DELETE statement when OUTPUT is in effect. This primarily affects the ORM when a flush is updating a row that contains server-calculated values, raising an error if the backend does not return the expected row count. PyODBC now states that it supports rowcount except if OUTPUT.inserted is present, which is taken into account by the ORM during a flush as to whether it will look for a rowcount.

  References: #4062

- [mssql] [bug] [orm]

  Enabled the “sane_rowcount” flag for the pymssql dialect, indicating that the DBAPI now reports the correct number of rows affected from an UPDATE or DELETE statement. This impacts mostly the ORM versioning feature in that it now can verify the number of rows affected on a target version.

- [mssql] [bug]

  Added a rule to SQL Server index reflection to ignore the so-called “heap” index that is implicitly present on a table that does not specify a clustered index.

  References: #4059

### oracle

- [oracle] [performance] [bug] [py2k]

  Fixed performance regression caused by the fix for #3937 where cx_Oracle as of version 5.3 dropped the `.UNICODE` symbol from its namespace, which was interpreted as cx_Oracle’s “WITH_UNICODE” mode being turned on unconditionally, which invokes functions on the SQLAlchemy side which convert all strings to unicode unconditionally and causing a performance impact. In fact, per cx_Oracle’s author the “WITH_UNICODE” mode has been removed entirely as of 5.1, so the expensive unicode conversion functions are no longer necessary and are disabled if cx_Oracle 5.1 or greater is detected under Python 2. The warning against “WITH_UNICODE” mode that was removed under #3937 is also restored.

  This change is also backported to: 1.1.13, 1.0.19

  References: #4035

- [oracle] [bug]

  Partial support for persisting and retrieving the Oracle value “infinity” is implemented with cx_Oracle, using Python float values only, e.g. `float("inf")`. Decimal support is not yet fulfilled by the cx_Oracle DBAPI driver.

  References: #4064

- [oracle] [bug]

  The cx_Oracle dialect has been reworked and modernized to take advantage of new patterns that weren’t present in the old 4.x series of cx_Oracle. This includes that the minimum cx_Oracle version is the 5.x series and that cx_Oracle 6.x is now fully tested. The most significant change involves type conversions, primarily regarding the numeric / floating point and LOB datatypes, making more effective use of cx_Oracle type handling hooks to simplify how bind parameter and result data is processed.

  See also

  Major Refactor to cx_Oracle Dialect, Typing System

- [oracle] [bug]

  two phase support for cx_Oracle has been completely removed for all versions of cx_Oracle, whereas in 1.2.0b1 this change only took effect for the 6.x series of cx_Oracle. This feature never worked correctly in any version of cx_Oracle and in cx_Oracle 6.x, the API which SQLAlchemy relied upon was removed.

  See also

  Major Refactor to cx_Oracle Dialect, Typing System

  References: #3997

- [oracle] [bug]

  The column keys present in a result set when using `Insert.returning()` with the cx_Oracle backend now use the correct column / label names like that of all other dialects. Previously, these came out as `ret_nnn`.

  See also

  Major Refactor to cx_Oracle Dialect, Typing System

- [oracle] [bug]

  Several parameters to the cx_Oracle dialect are now deprecated and will have no effect: `auto_setinputsizes`, `exclude_setinputsizes`, `allow_twophase`.

  See also

  Major Refactor to cx_Oracle Dialect, Typing System

- [oracle] [bug]

  Fixed bug where an index reflected under Oracle with an expression like “column DESC” would not be returned, if the table also had no primary key, as a result of logic that attempts to filter out the index implicitly added by Oracle onto the primary key columns.

  References: #4042

- [oracle] [bug]

  Fixed more regressions caused by cx_Oracle 6.0; at the moment, the only behavioral change for users is disconnect detection now detects for cx_Oracle.DatabaseError in addition to cx_Oracle.InterfaceError, as this behavior seems to have changed. Other issues regarding numeric precision and uncloseable connections are pending with the upstream cx_Oracle issue tracker.

  References: #4045

- [oracle] [bug]

  Fixed bug where Oracle 8 “non ansi” join mode would not add the `(+)` operator to expressions that used an operator other than the `=` operator. The `(+)` needs to be on all columns that are part of the right-hand side.

  References: #4076

## 1.2.0b2

Released: July 24, 2017

### orm

- [orm] [bug]

  Fixed regression from 1.1.11 where adding additional non-entity columns to a query that includes an entity with subqueryload relationships would fail, due to an inspection added in 1.1.11 as a result of #4011.

  This change is also backported to: 1.1.12

  References: #4033

- [orm] [bug]

  Fixed bug involving JSON NULL evaluation logic added in 1.1 as part of #3514 where the logic would not accommodate ORM mapped attributes named differently from the `Column` that was mapped.

  This change is also backported to: 1.1.12

  References: #4031

- [orm] [bug]

  Added `KeyError` checks to all methods within `WeakInstanceDict` where a check for `key in dict` is followed by indexed access to that key, to guard against a race against garbage collection that under load can remove the key from the dict after the code assumes its present, leading to very infrequent `KeyError` raises.

  This change is also backported to: 1.1.12

  References: #4030

### tests

- [tests] [bug] [py3k]

  Fixed issue in testing fixtures which was incompatible with a change made as of Python 3.6.2 involving context managers.

  This change is also backported to: 1.1.12, 1.0.18

  References: #4034

## 1.2.0b1

Released: July 10, 2017

### orm

- [orm] [feature]

  An `aliased()` construct can now be passed to the `Query.select_entity_from()` method. Entities will be pulled from the selectable represented by the `aliased()` construct. This allows special options for `aliased()` such as `aliased.adapt_on_names` to be used in conjunction with `Query.select_entity_from()`.

  This change is also backported to: 1.1.7

  References: #3933

- [orm] [feature]

  Added `.autocommit` attribute to `scoped_session`, proxying the `.autocommit` attribute of the underling `Session` currently assigned to the thread. Pull request courtesy Ben Fagin.

- [orm] [feature]

  Added a new feature `with_expression()` that allows an ad-hoc SQL expression to be added to a specific entity in a query at result time. This is an alternative to the SQL expression being delivered as a separate element in the result tuple.

  See also

  ORM attributes that can receive ad-hoc SQL expressions

  References: #3058

- [orm] [feature]

  Added a new style of mapper-level inheritance loading “polymorphic selectin”. This style of loading emits queries for each subclass in an inheritance hierarchy subsequent to the load of the base object type, using IN to specify the desired primary key values.

  See also

  “selectin” polymorphic loading, loads subclasses using separate IN queries

  References: #3948

- [orm] [feature]

  Added a new kind of eager loading called “selectin” loading. This style of loading is very similar to “subquery” eager loading, except that it uses an IN expression given a list of primary key values from the loaded parent objects, rather than re-stating the original query. This produces a more efficient query that is “baked” (e.g. the SQL string is cached) and also works in the context of `Query.yield_per()`.

  See also

  New “selectin” eager loading, loads all collections at once using IN

  References: #3944

- [orm] [feature]

  The `lazy="select"` loader strategy now makes used of the `BakedQuery` query caching system in all cases. This removes most overhead of generating a `Query` object and running it into a `select()` and then string SQL statement from the process of lazy-loading related collections and objects. The “baked” lazy loader has also been improved such that it can now cache in most cases where query load options are used.

  See also

  “Baked” loading now the default for lazy loads

  References: #3954

- [orm] [feature] [ext]

  The `Query.update()` method can now accommodate both hybrid attributes as well as composite attributes as a source of the key to be placed in the SET clause. For hybrids, an additional decorator `hybrid_property.update_expression()` is supplied for which the user supplies a tuple-returning function.

  See also

  Support for bulk updates of hybrids, composites

  References: #3229

- [orm] [feature]

  Added new attribute event `AttributeEvents.bulk_replace()`. This event is triggered when a collection is assigned to a relationship, before the incoming collection is compared with the existing one. This early event allows for conversion of incoming non-ORM objects as well. The event is integrated with the `@validates` decorator.

  See also

  New bulk_replace event

  References: #3896

- [orm] [feature]

  Added new event handler `AttributeEvents.modified()` which is triggered when the func:.attributes.flag_modified function is invoked, which is common when using the `sqlalchemy.ext.mutable` extension module.

  See also

  New “modified” event handler for sqlalchemy.ext.mutable

  References: #3303

- [orm] [bug]

  Fixed issue with subquery eagerloading which continues on from the series of issues fixed in #2699, #3106, #3893 involving that the “subquery” contains the correct FROM clause when beginning from a joined inheritance subclass and then subquery eager loading onto a relationship from the base class, while the query also includes criteria against the subclass. The fix in the previous tickets did not accommodate for additional subqueryload operations loading more deeply from the first level, so the fix has been further generalized.

  This change is also backported to: 1.1.11

  References: #4011

- [orm] [bug]

  Fixed bug where a cascade such as “delete-orphan” (but others as well) would fail to locate an object linked to a relationship that itself is local to a subclass in an inheritance relationship, thus causing the operation to not take place.

  This change is also backported to: 1.1.10

  References: #3986

- [orm] [bug]

  Fixed a race condition which could occur under threaded environments as a result of the caching added via #3915. An internal collection of `Column` objects could be regenerated on an alias object inappropriately, confusing a joined eager loader when it attempts to render SQL and collect results and resulting in an attribute error. The collection is now generated up front before the alias object is cached and shared among threads.

  This change is also backported to: 1.1.7

  References: #3947

- [orm] [bug]

  An UPDATE emitted as a result of the `relationship.post_update` feature will now integrate with the versioning feature to both bump the version id of the row as well as assert that the existing version number was matched.

  See also

  post_update integrates with ORM versioning

  References: #3496

- [orm] [bug]

  Repaired several use cases involving the `relationship.post_update` feature when used in conjunction with a column that has an “onupdate” value. When the UPDATE emits, the corresponding object attribute is now expired or refreshed so that the newly generated “onupdate” value can populate on the object; previously the stale value would remain. Additionally, if the target attribute is set in Python for the INSERT of the object, the value is now re-sent during the UPDATE so that the “onupdate” does not overwrite it (note this works just as well for server-generated onupdates). Finally, the `SessionEvents.refresh_flush()` event is now emitted for these attributes when refreshed within the flush.

  See also

  Refinements to post_update in conjunction with onupdate

  References: #3471, #3472

- [orm] [bug]

  Fixed bug where programmatic version_id counter in conjunction with joined table inheritance would fail if the version_id counter were not actually incremented and no other values on the base table were modified, as the UPDATE would have an empty SET clause. Since programmatic version_id where version counter is not incremented is a documented use case, this specific condition is now detected and the UPDATE now sets the version_id value to itself, so that concurrency checks still take place.

  References: #3996

- [orm] [bug]

  The versioning feature does not support NULL for the version counter. An exception is now raised if the version id is programmatic and was set to NULL for an UPDATE. Pull request courtesy Diana Clarke.

  References: #3673

- [orm] [bug]

  Removed a very old keyword argument from `scoped_session` called `scope`. This keyword was never documented and was an early attempt at allowing for variable scopes.

  See also

  “scope” keyword removed from scoped_session

  References: #3796

- [orm] [bug]

  Fixed bug where combining a “with_polymorphic” load in conjunction with subclass-linked relationships that specify joinedload with innerjoin=True, would fail to demote those “innerjoins” to “outerjoins” to suit the other polymorphic classes that don’t support that relationship. This applies to both a single and a joined inheritance polymorphic load.

  References: #3988

- [orm] [bug]

  Added new argument `with_for_update` to the `Session.refresh()` method. When the `Query.with_lockmode()` method were deprecated in favor of `Query.with_for_update()`, the `Session.refresh()` method was never updated to reflect the new option.

  See also

  Added “for update” arguments to Session.refresh

  References: #3991

- [orm] [bug]

  Fixed bug where a `column_property()` that is also marked as “deferred” would be marked as “expired” during a flush, causing it to be loaded along with the unexpiry of regular attributes even though this attribute was never accessed.

  References: #3984

- [orm] [bug]

  Fixed bug in subquery eager loading where the “join_depth” parameter for self-referential relationships would not be correctly honored, loading all available levels deep rather than correctly counting the specified number of levels for eager loading.

  References: #3967

- [orm] [bug]

  Added warnings to the LRU “compiled cache” used by the `Mapper` (and ultimately will be for other ORM-based LRU caches) such that when the cache starts hitting its size limits, the application will emit a warning that this is a performance-degrading situation that may require attention. The LRU caches can reach their size limits primarily if an application is making use of an unbounded number of `Engine` objects, which is an antipattern. Otherwise, this may suggest an issue that should be brought to the SQLAlchemy developer’s attention.

- [orm] [bug]

  Fixed bug to improve upon the specificity of loader options that take effect subsequent to the lazy load of a related entity, so that the loader options will match to an aliased or non-aliased entity more specifically if those options include entity information.

  References: #3963

- [orm] [bug]

  The `flag_modified()` function now raises `InvalidRequestError` if the named attribute key is not present within the object, as this is assumed to be present in the flush process. To mark an object “dirty” for a flush without referring to any specific attribute, the `flag_dirty()` function may be used.

  See also

  Use flag_dirty() to mark an object as “dirty” without any attribute changing

  References: #3753

- [orm] [bug]

  The “evaluate” strategy used by `Query.update()` and `Query.delete()` can now accommodate a simple object comparison from a many-to-one relationship to an instance, when the attribute names of the primary key / foreign key columns don’t match the actual names of the columns. Previously this would do a simple name-based match and fail with an AttributeError.

  References: #3366

- [orm] [bug]

  The `@validates` decorator now allows the decorated method to receive objects from a “bulk collection set” operation that have not yet been compared to the existing collection. This allows incoming values to be converted to compatible ORM objects as is already allowed from an “append” event. Note that this means that the `@validates` method is called for all values during a collection assignment, rather than just the ones that are new.

  See also

  A @validates method receives all values on bulk-collection set before comparison

  References: #3896

- [orm] [bug]

  Fixed bug in single-table inheritance where the select_from() argument would not be taken into account when limiting rows to a subclass. Previously, only expressions in the columns requested would be taken into account.

  See also

  Fixed issue involving single-table inheritance with select_from()

  References: #3891

- [orm] [bug]

  When assigning a collection to an attribute mapped by a relationship, the previous collection is no longer mutated. Previously, the old collection would be emptied out in conjunction with the “item remove” events that fire off; the events now fire off without affecting the old collection.

  See also

  Previous collection is no longer mutated upon replacement

  References: #3913

- [orm] [bug]

  The state of the `Session` is now present when the `SessionEvents.after_rollback()` event is emitted, that is, the attribute state of objects prior to their being expired. This is now consistent with the behavior of the `SessionEvents.after_commit()` event which also emits before the attribute state of objects is expired.

  See also

  The after_rollback() Session event now emits before the expiration of objects

  References: #3934

- [orm] [bug]

  Fixed bug where `Query.with_parent()` would not work if the `Query` were against an `aliased()` construct rather than a regular mapped class. Also adds a new parameter `with_parent.from_entity` to the standalone `with_parent()` function as well as `Query.with_parent()`.

  References: #3607

### orm declarative

- [orm] [declarative] [bug]

  Fixed bug where using `declared_attr` on an `AbstractConcreteBase` where a particular return value were some non-mapped symbol, including `None`, would cause the attribute to hard-evaluate just once and store the value to the object dictionary, not allowing it to invoke for subclasses. This behavior is normal when `declared_attr` is on a mapped class, and does not occur on a mixin or abstract class. Since `AbstractConcreteBase` is both “abstract” and actually “mapped”, a special exception case is made here so that the “abstract” behavior takes precedence for `declared_attr`.

  References: #3848

### engine

- [engine] [feature]

  Added native “pessimistic disconnection” handling to the `Pool` object. The new parameter `Pool.pre_ping`, available from the engine as `create_engine.pool_pre_ping`, applies an efficient form of the “pre-ping” recipe featured in the pooling documentation, which upon each connection check out, emits a simple statement, typically “SELECT 1”, to test the connection for liveness. If the existing connection is no longer able to respond to commands, the connection is transparently recycled, and all other connections made prior to the current timestamp are invalidated.

  See also

  Disconnect Handling - Pessimistic

  Pessimistic disconnection detection added to the connection pool

  References: #3919

- [engine] [bug]

  Added an exception handler that will warn for the “cause” exception on Py2K when the “autorollback” feature of `Connection` itself raises an exception. In Py3K, the two exceptions are naturally reported by the interpreter as one occurring during the handling of the other. This is continuing with the series of changes for rollback failure handling that were last visited as part of #2696 in 1.0.12.

  This change is also backported to: 1.1.7

  References: #3946

- [engine] [bug]

  Fixed bug where in the unusual case of passing a `Compiled` object directly to `Connection.execute()`, the dialect with which the `Compiled` object were generated was not consulted for the paramstyle of the string statement, instead assuming it would match the dialect-level paramstyle, causing mismatches to occur.

  References: #3938

### sql

- [sql] [feature]

  Added a new kind of `bindparam()` called “expanding”. This is for use in `IN` expressions where the list of elements is rendered into individual bound parameters at statement execution time, rather than at statement compilation time. This allows both a single bound parameter name to be linked to an IN expression of multiple elements, as well as allows query caching to be used with IN expressions. The new feature allows the related features of “select in” loading and “polymorphic in” loading to make use of the baked query extension to reduce call overhead. This feature should be considered to be experimental for 1.2.

  See also

  Late-expanded IN parameter sets allow IN expressions with cached statements

  References: #3953

- [sql] [feature] [mysql] [oracle] [postgresql]

  Added support for SQL comments on `Table` and `Column` objects, via the new `Table.comment` and `Column.comment` arguments. The comments are included as part of DDL on table creation, either inline or via an appropriate ALTER statement, and are also reflected back within table reflection, as well as via the `Inspector`. Supported backends currently include MySQL, PostgreSQL, and Oracle. Many thanks to Frazer McLean for a large amount of effort on this.

  See also

  Support for SQL Comments on Table, Column, includes DDL, reflection

  References: #1546

- [sql] [feature]

  The longstanding behavior of the `ColumnOperators.in_()` and `ColumnOperators.notin_()` operators emitting a warning when the right-hand condition is an empty sequence has been revised; a simple “static” expression of “1 != 1” or “1 = 1” is now rendered by default, rather than pulling in the original left-hand expression. This causes the result for a NULL column comparison against an empty set to change from NULL to true/false. The behavior is configurable, and the old behavior can be enabled using the `create_engine.empty_in_strategy` parameter to `create_engine()`.

  See also

  The IN / NOT IN operator’s empty collection behavior is now configurable; default expression simplified

  References: #3907

- [sql] [feature]

  Added a new option `autoescape` to the “startswith” and “endswith” classes of comparators; this supplies an escape character also applies it to all occurrences of the wildcard characters “%” and “_” automatically. Pull request courtesy Diana Clarke.

  Note

  This feature has been changed as of 1.2.0 from its initial implementation in 1.2.0b2 such that autoescape is now passed as a boolean value, rather than a specific character to use as the escape character.

  See also

  New “autoescape” option for startswith(), endswith()

  References: #2694

- [sql] [bug]

  Fixed AttributeError which would occur in `WithinGroup` construct during an iteration of the structure.

  This change is also backported to: 1.1.11

  References: #4012

- [sql] [bug]

  Fixed regression released in 1.1.5 due to #3859 where adjustments to the “right-hand-side” evaluation of an expression based on `Variant` to honor the underlying type’s “right-hand-side” rules caused the `Variant` type to be inappropriately lost, in those cases when we do want the left-hand side type to be transferred directly to the right hand side so that bind-level rules can be applied to the expression’s argument.

  This change is also backported to: 1.1.9

  References: #3952

- [sql] [bug] [postgresql]

  Changed the mechanics of `ResultProxy` to unconditionally delay the “autoclose” step until the `Connection` is done with the object; in the case where PostgreSQL ON CONFLICT with RETURNING returns no rows, autoclose was occurring in this previously non-existent use case, causing the usual autocommit behavior that occurs unconditionally upon INSERT/UPDATE/DELETE to fail.

  This change is also backported to: 1.1.9

  References: #3955

- [sql] [bug]

  The rules for type coercion between `Numeric`, `Integer`, and date-related types now include additional logic that will attempt to preserve the settings of the incoming type on the “resolved” type. Currently the target for this is the `asdecimal` flag, so that a math operation between `Numeric` or `Float` and `Integer` will preserve the “asdecimal” flag as well as if the type should be the `Float` subclass.

  See also

  Stronger typing added to “float” datatypes

  References: #4018

- [sql] [bug] [mysql]

  The result processor for the `Float` type now unconditionally runs values through the `float()` processor if the dialect specifies that it also supports “native decimal” mode. While most backends will deliver Python `float` objects for a floating point datatype, the MySQL backends in some cases lack the typing information in order to provide this and return `Decimal` unless the float conversion is done.

  See also

  Stronger typing added to “float” datatypes

  References: #4020

- [sql] [bug]

  Added some extra strictness to the handling of Python “float” values passed to SQL statements. A “float” value will be associated with the `Float` datatype and not the Decimal-coercing `Numeric` datatype as was the case before, eliminating a confusing warning emitted on SQLite as well as unnecessary coercion to Decimal.

  See also

  Stronger typing added to “float” datatypes

  References: #4017

- [sql] [bug]

  The operator precedence for all comparison operators such as LIKE, IS, IN, MATCH, equals, greater than, less than, etc. has all been merged into one level, so that expressions which make use of these against each other will produce parentheses between them. This suits the stated operator precedence of databases like Oracle, MySQL and others which place all of these operators as equal precedence, as well as PostgreSQL as of 9.5 which has also flattened its operator precedence.

  See also

  Flattened operator precedence for comparison operators

  References: #3999

- [sql] [bug]

  Repaired issue where the type of an expression that used `ColumnOperators.is_()` or similar would not be a “boolean” type, instead the type would be “nulltype”, as well as when using custom comparison operators against an untyped expression. This typing can impact how the expression behaves in larger contexts as well as in result-row-handling.

  References: #3873

- [sql] [bug]

  Fixed the negation of a `Label` construct so that the inner element is negated correctly, when the `not_()` modifier is applied to the labeled expression.

  References: #3969

- [sql] [bug]

  The system by which percent signs in SQL statements are “doubled” for escaping purposes has been refined. The “doubling” of percent signs mostly associated with the `literal_column` construct as well as operators like `ColumnOperators.contains()` now occurs based on the stated paramstyle of the DBAPI in use; for percent-sensitive paramstyles as are common with the PostgreSQL and MySQL drivers the doubling will occur, for others like that of SQLite it will not. This allows more database-agnostic use of the `literal_column` construct to be possible.

  See also

  Percent signs in literal_column() now conditionally escaped

  References: #3740

- [sql] [bug]

  Fixed bug where a column-level `CheckConstraint` would fail to compile the SQL expression using the underlying dialect compiler as well as apply proper flags to generate literal values as inline, in the case that the sqltext is a Core expression and not just a plain string. This was long-ago fixed for table-level check constraints in 0.9 as part of #2742, which more commonly feature Core SQL expressions as opposed to plain string expressions.

  References: #3957

- [sql] [bug]

  Fixed bug where a SQL-oriented Python-side column default could fail to be executed properly upon INSERT in the “pre-execute” codepath, if the SQL itself were an untyped expression, such as plain text. The “pre- execute” codepath is fairly uncommon however can apply to non-integer primary key columns with SQL defaults when RETURNING is not used.

  References: #3923

- [sql] [bug]

  The expression used for COLLATE as rendered by the column-level `collate()` and `ColumnOperators.collate()` is now quoted as an identifier when the name is case sensitive, e.g. has uppercase characters. Note that this does not impact type-level collation, which is already quoted.

  See also

  The column-level COLLATE keyword now quotes the collation name

  References: #3785

- [sql] [bug]

  Fixed bug where the use of an `Alias` object in a column context would raise an argument error when it tried to group itself into a parenthesized expression. Using `Alias` in this way is not yet a fully supported API, however it applies to some end-user recipes and may have a more prominent role in support of some future PostgreSQL features.

  References: #3939

### schema

- [schema] [bug]

  An `ArgumentError` is now raised if a `ForeignKeyConstraint` object is created with a mismatched number of “local” and “remote” columns, which otherwise causes the internal state of the constraint to be incorrect. Note that this also impacts the condition where a dialect’s reflection process produces a mismatched set of columns for a foreign key constraint.

  This change is also backported to: 1.1.10

  References: #3949

### postgresql

- [postgresql] [bug]

  Continuing with the fix that correctly handles PostgreSQL version string “10devel” released in 1.1.8, an additional regexp bump to handle version strings of the form “10beta1”. While PostgreSQL now offers better ways to get this information, we are sticking w/ the regexp at least through 1.1.x for the least amount of risk to compatibility w/ older or alternate PostgreSQL databases.

  This change is also backported to: 1.1.11

  References: #4005

- [postgresql] [bug]

  Fixed bug where using `ARRAY` with a string type that features a collation would fail to produce the correct syntax within CREATE TABLE.

  This change is also backported to: 1.1.11

  References: #4006

- [postgresql] [bug]

  Added “autocommit” support for GRANT, REVOKE keywords. Pull request courtesy Jacob Hayes.

  This change is also backported to: 1.1.10

- [postgresql] [bug]

  Added support for parsing the PostgreSQL version string for a development version like “PostgreSQL 10devel”. Pull request courtesy Sean McCully.

  This change is also backported to: 1.1.8

- [postgresql] [bug]

  Fixed bug where the base `ARRAY` datatype would not invoke the bind/result processors of `ARRAY`.

  References: #3964

- [postgresql] [bug]

  Added support for all possible “fields” identifiers when reflecting the PostgreSQL `INTERVAL` datatype, e.g. “YEAR”, “MONTH”, “DAY TO MINUTE”, etc.. In addition, the `INTERVAL` datatype itself now includes a new parameter `INTERVAL.fields` where these qualifiers can be specified; the qualifier is also reflected back into the resulting datatype upon reflection / inspection.

  See also

  Support for fields specification in INTERVAL, including full reflection

  References: #3959

### mysql

- [mysql] [feature]

  Added support for MySQL’s ON DUPLICATE KEY UPDATE MySQL-specific `Insert` object. Pull request courtesy Michael Doronin.

  See also

  Support for INSERT..ON DUPLICATE KEY UPDATE

  References: #4009

- [mysql] [bug]

  MySQL 5.7 has introduced permission limiting for the “SHOW VARIABLES” command; the MySQL dialect will now handle when SHOW returns no row, in particular for the initial fetch of SQL_MODE, and will emit a warning that user permissions should be modified to allow the row to be present.

  This change is also backported to: 1.1.11

  References: #4007

- [mysql] [bug]

  Removed an ancient and unnecessary intercept of the UTC_TIMESTAMP MySQL function, which was getting in the way of using it with a parameter.

  This change is also backported to: 1.1.10

  References: #3966

- [mysql] [bug]

  Fixed bug in MySQL dialect regarding rendering of table options in conjunction with PARTITION options when rendering CREATE TABLE. The PARTITION related options need to follow the table options, whereas previously this ordering was not enforced.

  This change is also backported to: 1.1.10

  References: #3961

- [mysql] [bug]

  Added support for views that are unreflectable due to stale table definitions, when calling `MetaData.reflect()`; a warning is emitted for the table that cannot respond to `DESCRIBE`, but the operation succeeds.

  References: #3871

### mssql

- [mssql] [bug]

  Fixed bug where SQL Server transaction isolation must be fetched from a different view when using Azure data warehouse, the query is now attempted against both views and then a NotImplemented is raised unconditionally if failure continues to provide the best resiliency against future arbitrary API changes in new SQL Server versions.

  This change is also backported to: 1.1.11

  References: #3994

- [mssql] [bug]

  Added a placeholder type `XML` to the SQL Server dialect, so that a reflected table which includes this type can be re-rendered as a CREATE TABLE. The type has no special round-trip behavior nor does it currently support additional qualifying arguments.

  This change is also backported to: 1.1.11

  References: #3973

- [mssql] [bug]

  The SQL Server dialect now allows for a database and/or owner name with a dot inside of it, using brackets explicitly in the string around the owner and optionally the database name as well. In addition, sending the `quoted_name` construct for the schema name will not split on the dot and will deliver the full string as the “owner”. `quoted_name` is also now available from the `sqlalchemy.sql` import space.

  See also

  SQL Server schema names with embedded dots supported

  References: #2626

### oracle

- [oracle] [feature] [postgresql]

  Added new keywords `Sequence.cache` and `Sequence.order` to `Sequence`, to allow rendering of the CACHE parameter understood by Oracle and PostgreSQL, and the ORDER parameter understood by Oracle. Pull request courtesy David Moore.

  This change is also backported to: 1.1.12

- [oracle] [feature]

  The Oracle dialect now inspects unique and check constraints when using `Inspector.get_unique_constraints()`, `Inspector.get_check_constraints()`. As Oracle does not have unique constraints that are separate from a unique `Index`, a `Table` that’s reflected will still continue to not have `UniqueConstraint` objects associated with it. Pull requests courtesy Eloy Felix.

  See also

  Oracle Unique, Check constraints now reflected

  References: #4003

- [oracle] [bug]

  Support for two-phase transactions has been removed entirely for cx_Oracle when version 6.0b1 or later of the DBAPI is in use. The two- phase feature historically has never been usable under cx_Oracle 5.x in any case, and cx_Oracle 6.x has removed the connection-level “twophase” flag upon which this feature relied.

  This change is also backported to: 1.1.11

  References: #3997

- [oracle] [bug]

  Fixed bug in cx_Oracle dialect where version string parsing would fail for cx_Oracle version 6.0b1 due to the “b” character. Version string parsing is now via a regexp rather than a simple split.

  This change is also backported to: 1.1.10

  References: #3975

- [oracle] [bug]

  The cx_Oracle dialect now supports “sane multi rowcount”, that is, when a series of parameter sets are executed via DBAPI `cursor.executemany()`, we can make use of `cursor.rowcount` to verify the number of rows matched. This has an impact within the ORM when detecting concurrent modification scenarios, in that some simple conditions can now be detected even when the ORM is batching statements, as well as when the more strict versioning feature is used, the ORM can still use statement batching. The flag is enabled for cx_Oracle assuming at least version 5.0, which is now commonplace.

  References: #3932

- [oracle] [bug]

  Oracle reflection now “normalizes” the name given to a foreign key constraint, that is, returns it as all lower case for a case insensitive name. This was already the behavior for indexes and primary key constraints as well as all table and column names. This will allow Alembic autogenerate scripts to compare and render foreign key constraint names correctly when initially specified as case insensitive.

  See also

  Oracle foreign key constraint names are now “name normalized”

  References: #3276

### misc

- [feature] [ext]

  Added new flag `Session.enable_baked_queries` to the `Session` to allow baked queries to be disabled session-wide, reducing memory use. Also added new `Bakery` wrapper so that the bakery returned by `BakedQuery.bakery` can be inspected.

- [bug] [ext]

  Protected against testing “None” as a class in the case where declarative classes are being garbage collected and new automap prepare() operations are taking place concurrently, very infrequently hitting a weakref that has not been fully acted upon after gc.

  This change is also backported to: 1.1.10

  References: #3980

- [bug] [ext]

  Fixed bug in `sqlalchemy.ext.mutable` where the `Mutable.as_mutable()` method would not track a type that had been copied using `TypeEngine.copy()`. This became more of a regression in 1.1 compared to 1.0 because the `TypeDecorator` class is now a subclass of `SchemaEventTarget`, which among other things indicates to the parent `Column` that the type should be copied when the `Column` is. These copies are common when using declarative with mixins or abstract classes.

  This change is also backported to: 1.1.8

  References: #3950

- [bug] [ext]

  Added support for bound parameters, e.g. those normally set up via `Query.params()`, to the `Result.count()` method. Previously, support for parameters were omitted. Pull request courtesy Pat Deegan.

  This change is also backported to: 1.1.8

- [bug] [ext]

  The `AssociationProxy.any()`, `AssociationProxy.has()` and `AssociationProxy.contains()` comparison methods now support linkage to an attribute that is itself also an `AssociationProxy`, recursively.

  See also

  AssociationProxy any(), has(), contains() work with chained association proxies

  References: #3769

- [bug] [ext]

  Implemented in-place mutation operators `__ior__`, `__iand__`, `__ixor__` and `__isub__` for `MutableSet` and `__iadd__` for `MutableList` so that change events are fired off when these mutator methods are used to alter the collection.

  See also

  In-place mutation operators work for MutableSet, MutableList

  References: #3853

- [bug] [declarative]

  A warning is emitted if the `declared_attr.cascading` modifier is used with a declarative attribute that is itself declared on a class that is to be mapped, as opposed to a declarative mixin class or `__abstract__` class. The `declared_attr.cascading` modifier currently only applies to mixin/abstract classes.

  References: #3847

- [bug] [ext]

  Improved the association proxy list collection so that premature autoflush against a newly created association object can be prevented in the case where `list.append()` is being used, and a lazy load would be invoked when the association proxy accesses the endpoint collection. The endpoint collection is now accessed first before the creator is invoked to produce the association object.

  References: #3941

- [bug] [ext]

  The `sqlalchemy.ext.hybrid.hybrid_property` class now supports calling mutators like `@setter`, `@expression` etc. multiple times across subclasses, and now provides a `@getter` mutator, so that a particular hybrid can be repurposed across subclasses or other classes. This now matches the behavior of `@property` in standard Python.

  See also

  Hybrid attributes support reuse among subclasses, redefinition of @getter

  References: #3911, #3912

- [bug] [ext]

  Fixed a bug in the `sqlalchemy.ext.serializer` extension whereby an “annotated” SQL element (as produced by the ORM for many types of SQL expressions) could not be reliably serialized. Also bumped the default pickle level for the serializer to “HIGHEST_PROTOCOL”.

  References: #3918