Fetching entities with Composite Key Relations

[michalbundyra]

In our database design we are using entities with composite keys, and we are using composite keys relations between entities.

Let say we have the following entities with Primary Keys (PK):

• Company (PK: company_code)
• Customer (PK composite: company_code + customer_code)
• Invoice (PK composite: company_code + invoice_code)

and the following relations in Invoice:

• to Company (using company_code), not nullable
• to Customer (using composite key company_code + customer_code), nullable

Now we have company_code (not null) but no customer_code (null).
We want to fetch Invoice entity, so that we get not null Company, and null Customer.

The problem is that loading Invoice with null Customer is not working - we are getting the following exception:

Exception: [Doctrine\Common\Proxy\Exception\OutOfBoundsException] Missing value for primary key code on Doctrine\Tests\Models\CompositeKeyRelations\CustomerClass

This PR provide a fix, to load the Customer in the described case.
The change is pretty simply, and no other tests are affected.

NOTE: Loading Company is not a problem as it is using relation on just one column (not a composite key). The description includes it just for completeness of the example.