Bug Report

ManyToMany IndexBy not working on multiple fields after upgrade to symfony 4.3
Previously ther was no problem

Versions:
doctrine/annotations v1.8.0
doctrine/cache 1.10.0
doctrine/collections 1.6.4
doctrine/common 2.12.0
doctrine/dbal v2.10.1
doctrine/doctrine-bundle 2.0.7
doctrine/doctrine-migrations-bundle 2.1.2
doctrine/event-manager 1.1.0
doctrine/inflector 1.3.1
doctrine/instantiator 1.3.0
doctrine/lexer 1.2.0
doctrine/migrations 2.2.1
doctrine/orm v2.7.0
doctrine/persistence 1.3.6
doctrine/reflection v1.1.0

Summary

I have a many-to-many relation roles <-> user_roles <--> users

tables fields names (LOOK OUT THEY ARE DIFERENT):

[id_role] <---> [role_id, user_id] <--> [id]

with COMPOSITE PRIMARY index [user_id, role_id] (primary to be UNIQUE key), but it fails after upgrade

You can see more here: https://www.doctrine-project.org/projects/doctrine-orm/en/2.7/tutorials/working-with-indexed-associations.html

Reason to do that is:

When calling Collection::containsKey($key) on one-to-many and many-to-many collections using indexBy and EXTRA_LAZY a query is now executed to check for the existance for the item. Prevoiusly this operation was performed in memory by loading all entities of the collection.
From https://doctrine2.readthedocs.io/en/latest/changelog/migration_2_5.html

Current behavior

Error:

request.CRITICAL: Uncaught PHP Exception Doctrine\ORM\Mapping\MappingException: "No mapping found for field 'role_id, user_id' on class 'App\Entity\.....\Role'." at /....../vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/MappingException.php line 163 {"exception":"[object] (Doctrine\\ORM\\Mapping\\MappingException(code: 0): No mapping found for field 'role_id, user_id' on class 'App\\Entity\\....\\Role'. at /...../vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/MappingException.php:163)"} []

ClassMetadtaInfo.getAssociationMapping() try to find $this->associationMappings['role_id, user_id']
as it thins "'role_id, user_id'" is one fieldname

How to reproduce

CLASS ROLE

	/**
	 * @ORM\ManyToMany(targetEntity="App\Entity\.....\User", mappedBy="id_role")
	 */
	protected $users;


CLASS USER
    /**
     * //indexBy="role_id, user_id", 
     * 
     * @ORM\ManyToMany(targetEntity="App\Entity\....\Role", **indexBy="role_id, user_id",** fetch="EXTRA_LAZY", inversedBy="users", cascade={"persist"})
     * @ORM\JoinTable(name="sec_user_roles", 
     *     joinColumns={@ORM\JoinColumn(name="user_id", referencedColumnName="id", nullable=false)},
     *     inverseJoinColumns={@ORM\JoinColumn(name="role_id", referencedColumnName="id_role", nullable=false)}
     */
    protected $roles;

if you remove indexBy="role_id, user_id", IT WORKS.
Before update, here was no problem.

i tried:

indexBy="user_id, role_id"
indexBy="user_id"

none worked

Expected behavior

Not to fail getting user entity