Clarify that "query_builder" must have displayed entity in from()

[webmozart]

We had this "bug report":

$qb = $this->getEntityManager()->createQueryBuilder();
$qb
    ->select('DISTINCT b')
    ->from('TestBundle:EntityA', 'a')
    ->innerJoin('TestBundle:EntityB', 'b', Expr\Join::WITH, $qb->expr()->eq('a.key', 'b'))
    ->where(
        $qb->expr()->eq('b.flag', ':flagValue')
    )
    ->setParameter('flagValue', 1)
;

The problem here is that the select() does not select from the from() table, but the joined one. The documentation should clarify that the select() should go to the from() table only for entity fields.

[wouterj]

I think this is out of scope for the symfony documentation. We aren't documenting Doctrine, we are only documenting the Symfony integration of Doctrine.
Doctrine should make sure they documented this.

[webmozart]

I disagree. The issue is Symfony's because we explicitly fetch the choices using the ID field in the root table.

[xabbuh]

@webmozart So, do I understand correctly that one should select a in your example because that selected object is later on used in the Form component to compare choices?

[webmozart]

@xabbuh yes, exactly

[wouterj]

Ah, I'm sorry @webmozart you are correct. I did not see the referenced issue and thought you were talking about doctrine only (not integrated in the forms).