Bad join parsing with multiple keys

[EdaCZ]

• bug report? yes
• feature request? no
• version: 2.4.2, PHP 7.0.19, MySQL 5.7

Description

When there are two foreign keys on table Operator, one Operator.countryId -> Country.id and second Operator.countryId, Operator.regionOrder -> Region (id, order), when you want to order selection of operators by joined column, it throws notice Array to string conversion on /Database/Table/SqlBuilder.php:787.

$this->db->table('Operator')->order('countryId.id')->count();

Caution: It depends on order of foreign keys, in which they are stored in database.

Nette Database should choose simple key for joining, but now it chooses two-column foreign key (depends on order of FKs in DB).

Steps To Reproduce

• Install nette sandbox
• install SQL scheme

CREATE TABLE `Country` (
  `id` int(4) unsigned NOT NULL AUTO_INCREMENT,
  `short` varchar(10) COLLATE utf8_czech_ci NOT NULL,
  `title` varchar(50) COLLATE utf8_czech_ci NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;

CREATE TABLE `Operator` (
  `id` int(4) unsigned NOT NULL AUTO_INCREMENT,
  `title` varchar(50) COLLATE utf8_czech_ci NOT NULL,
  `countryId` int(4) unsigned NOT NULL,
  `regionOrder` int(1) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `Operator_ibfk_6` (`countryId`,`regionOrder`),
  KEY `regionOrder` (`regionOrder`),
  CONSTRAINT `Operator_ibfk_11` FOREIGN KEY (`countryId`) REFERENCES `Country` (`id`),
  CONSTRAINT `Operator_ibfk_12` FOREIGN KEY (`countryId`, `regionOrder`) REFERENCES `Region` (`id`, `order`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;

CREATE TABLE `Region` (
  `id` int(4) unsigned NOT NULL,
  `order` int(1) unsigned NOT NULL,
  `title` varchar(50) COLLATE utf8_czech_ci NOT NULL,
  `countryId` int(4) unsigned NOT NULL,
  PRIMARY KEY (`id`,`order`),
  KEY `countryId` (`countryId`),
  KEY `order` (`order`),
  CONSTRAINT `Region_ibfk_2` FOREIGN KEY (`countryId`) REFERENCES `Country` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;

• call code:

$this->db->table('Operator')->order('countryId.id')->count();

• if it did not throw an error, change order of foreign keys, in which they are stored, on table Operator