Doctrine_Relation_ForeignKey::fetchRelatedFor() executes the following code at line 70:

$coll = $this->getTable()>getConnection()>query($dql, $id);
$related = $coll[0];

As you can see it accesses the first element by using index "0" in $coll and hence ignores a modified ATTR_COLL_KEY-setting, for instance:

$this->setAttribute(Doctrine_Core::ATTR_COLL_KEY, 'id');

Fortunately I had two models (ForeignA and ForeignB) in my project which both have an one-to-one relation to a third model (Main). That helped me finding this bug which causes the following strange behavior:

// program 1:

$m = new Main();
$m->name = 'M1';
$m->setForeignA(new ForeignA()); // has ATTR_COLL_KEY changed to 'id'
$m->setForeignB(new ForeignB());
$m->save();

// program 2:

$m = Doctrine_Core::getTable('M1')->findOneBy('name', 'M1');
$m->getForeignA()->exists(); // false
$m->getForeignB()->exists(); // true

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The big problem about this issue is that behavior is inconsistent. If you don't split the example above into two separate programs/processes you won't have problems, since Doctrine accesses the reference which was stored when calling save().

You will get into trouble using functional tests in Symfony. Since there is only a single process for all requests I wasn't able to reproduce a problem caused by this bug which appeared in the production environment.

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Edit:

Doctrine_Connection::queryOne() is affected as well!

A solution is to replace

$coll = $this->getTable()>getConnection()>query($dql, $id);
$related = $coll[0];

by

$related = $this->getTable()>getConnection()>query($dql, $id)->getFirst();