Add the ability to add "INSTANCE OF" for Criteria Expression Comparison about collections

[7ochem]

I wanted to filter a collection by a specific type and ran into the same issue:

$object->getItems()->matching(
    Criteria::create()->where(
        Criteria::expr()->instanceOf(Some::class)
    )
);

But instanceOf() obviously does not exist. The "items" here is a collection of subtypes which all extend some base class.

If this is still a thing, then I could take a shot at this and try to add it to doctrine/collections and doctrine/orm

[trickeyone]

@7ochem It looks like my PR (#249) was accepted and added to 1.6.8, which restored only strict-checking for scalar values. This re-enabled my original work-around. That said, I think having an equivalent of INSTANCE OF for collections would be extremely beneficial.

[Ocramius]

Duplicate of doctrine/orm#5908

[trickeyone]

Thanks @Ocramius! Didn't know there was a request on the main doctrine2 project.

[trickeyone]

As a note, I've found that if I use:

$type1 = new Type\Type1();
$type2 = new Type\Type2();
Criteria::expr()->andWhere(
  'field',
  Criteria::expr()->in([$type1, $type2])
);

Where Type/Type1 and Type/Type2 are discriminators with IDs, the desired outcome can be achieved.

[trickeyone]

Followup on my previous comment. My solution that did work for 1.4 doesn't work with 1.5 because the Comparison::IN comparator now does a strict in_array