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Mapping Java Objects with JPA
The document outlines the Java Persistence API (JPA) 2.0 and its role in object-relational mapping, detailing its development history, key concepts, and annotations used for persistence. JPA is a specification that allows flexibility in ORM implementations, with Hibernate being the most popular provider. The document also presents a model for an employee management system, illustrating how JPA can simplify database operations through annotations.
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Mapping Java Objects with JPA
- 1. Mapping Objects WithJPA Java Persistence API 2.0 Aaron Schram University of Colorado at Boulder Thursday, March 31, 2011
- 2. Me PhD Candidate at the University of Colorado Prior to returning to CU I held several software engineering positions Mocapay, Inc. (Mobile Payments) Rally Software Development (Agile Tooling) BEA Systems (Weblogic Portal, Now Oracle) Lockheed Martin (IS & GS) Thursday, March 31, 2011
- 3. Some History Thursday, March31, 2011
- 4. History A result of the JSR 317 Expert Group Members included Sun Microsystems, Inc. Oracle BEA Systems* IBM VMWare Thursday, March 31, 2011
- 5. History Cont... Developed as a replacement for EJB 2 entity beans Version 2.0 was released Dec 10th, 2009 Covers 2 areas of Object Relational Mapping (ORM) Object relational metadata Java Persistence Query Language (JPQL) Thursday, March 31, 2011
- 6. History Cont... JPA 2.0 included consensus approval for new features Expanded ORM functionality Criteria query API Standardization of query hints Standardization of metadata for DDL generation Validation support Thursday, March 31, 2011
- 7. It’s Just ASpecification* JPA is a specification used to detail what a reference provider should conform to when providing ORM functionality It’s actually more than just a specification A finalized Java Specification Request will include a reference implementation Since JPA is a finalized JSR an implementation is provided There are many JPA reference implementations Hibernate, EclipseLink, OpenJPA Thursday, March 31, 2011
- 8. Hibernate The most popular JPA vendor is Hibernate (JBoss) JPA 1.0 was heavily influenced by Gavin King, the creator of Hibernate Much of what exists in JPA is adopted directly from the Hibernate project Many key concepts such as mapping syntax and central session/entity management exist in both Thursday, March 31, 2011
- 9. Key Concepts JPA utilizes annotated Plain Old Java Objects (POJOs) Define an EntityBean for persistence @Entity Define relationships between beans @OneToOne @OneToMany @ManyToOne @ManyToMany Thursday, March 31, 2011
- 10. Key Concepts Cont... Primitive types and wrappers are mapped by default String, Long, Integers, Double, etc. Mappings can be defined on instance vars or on accessor methods of the POJO Supports inheritance and embedding EntityManger is used to manage the state and life cycle of all entities within a give persistence context Primary keys are generated and accessed via @Id annotation Thursday, March 31, 2011
- 11. An Example Thursday, March31, 2011
- 12. Office-Employees Example This was a common interview question at one of my previous employers Thursday, March 31, 2011
- 13. Question: How could you model an employee management system using an ORM? Thursday, March 31, 2011
- 14. In the interviewwe Question Details would build the whole application Design an application that allows a customer to view all employees that physically reside in a specific office Each employee may only reside in one office Employees must have First name, last name, phone number, id Each office must have Here, we’ll just build Name, postal address, id out the model tier Any ORM will do, we’ll use JPA... Thursday, March 31, 2011
- 15. The Model Thursday, March31, 2011
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- 17. From Model toCode Our model contains four classes Office Employee DomainObject PostalAddress Office and Employee inherit from DomainObject DomainObject holds on to best practice attributes such as id, creation date, modified date, version, etc. Thursday, March 31, 2011
- 18. From Model toCode Cont... @Entity must be used to tell JPA which classes are eligible for persistence @ManyToOne must be used to tell JPA there is an aggregation between Office and Employee We’ll show a use of @Embedded and @Embeddable for the Office-PostalAddress relationship As well as inheritance using @MappedSuperclass Thursday, March 31, 2011
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- 20. This class isnot to be directly persisted DB generated Id For optimistic locking Store as datetime Call these methods before creation and modification Thursday, March 31, 2011
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- 22. Eligible for persistence Embed PostalAddress in the same table as Office Thursday, March 31, 2011
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- 24. Allow this objectto be embedded by other objects State is an Enum that will be treated as a String (varchar) Thursday, March 31, 2011
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- 26. Eligible for persistence Defines the many to one association with Office Thursday, March 31, 2011
- 27. Explanation @Embeddable and @Embedded Allows for the attributes of an embedded class to be stored in the same table as the embedding class @Enumerated Allows for the value of an Enum to be stored in a column in the class’s database table @MappedSuperclass Allows for all attributes of the superclass to be utilized by the subclasses Duplicates all superclass attributes on subclass tables Thursday, March 31, 2011
- 28. The Database Thursday, March31, 2011
- 29. The Database JPA is capable of generating the underlying database for the developer Most aspects of the generation are available for customization The defaults are generally good enough Any @Entity causes the generation of a database table. Our generated tables are: Office table Employee table Thursday, March 31, 2011
- 30. Office Table Field Type id bigint(20) createDate datetime modifiedDate datetime version int(11) name varchar(255) addressOne varchar(255) addressTwo varchar(255) city varchar(255) state varchar(255) zipCode varchar(255) Thursday, March 31, 2011
- 31. Employee Table Field Type id bigint(20) createDate datetime modifiedDate datetime version int(11) firstName varchar(255) lastName varchar(255) FK to location varchar(255) Office phoneNumber varchar(255) office_id bigint(20) Thursday, March 31, 2011
- 32. Take Aways Thursday, March31, 2011
- 33. Take Aways JPA is a specification that a developer can code to in order to easily leverage ORM technologies There are a wide variety of vendors that implement the specification Coding to the spec allows the developer to be flexible in their choice of vendor implementations with limited ripple throughout the codebase JPA greatly simplifies persistence of POJOs through a small set of easily utilized annotations Thursday, March 31, 2011
- 34. Questions? Aaron Schram [email protected] Thursday, March 31, 2011
