[5.8] Handle duplicates method in eloquent collections

[timacdonald]

This PR handles the new $collection->duplicates() method for eloquent collections.

The eloquent collection method compares entities with the $a->is($b) comparison. If you think it should just compare keys $a->getKey() === $b->getKey() than I can switch it over. The only time I see this being an issue is if a collection contains two models with the same key from different tables or something like that - which I can't imagine happening - but is something to consider.

Note that the eloquent method does not alter functionality with strict mode. I've written more about this below. It currently matches how unique() method works: #28193

[timacdonald]

Here is a bit more info on the strict / loose comparison and why: When it comes to eloquent models how should comparison work. Should eloquent models be treated differently? Because as it stands, they are.

The existing unique method bypasses strict comparison and is solely based on the keys. So if you have two different instances of a model, both with the same key...

$one = User::find(22);
$two = User::find(22);
$three = User::find(22);

$users = (new User)->newCollection([$one, $two, $three]);

$users->unique($key = null, $strict = true);

Doing this will result in a collection that only contains $three. Which raises the question - how do we strict compare models - but also points out how Laravel currently strict compares models.

Being that unique and duplicates share a similar problem space, I think it makes sense to match existing comparison functionality.

$one = User::find(22);
$two = User::find(22);
$three = User::find(22);

$users = (new User)->newCollection([$one, $two, $three]);

$users->duplicates($key = null, $strict = true);

Which results in a collection containing $two and $three.

If you ran unique and got the above result, and then ran duplicates and got an empty collection - those two are conflicting results for a similar problem. The following illustrates how you would end up with a collection with one unique item, but no duplicates...

$one = User::find(22);
$two = User::find(22);
$three = User::find(22);

$users = (new User)->newCollection([$one, $two, $three]);

$users->unique($key = null, $strict = true);
// [$three]

$users->duplicates($key = null, $strict = true);
// []

I think it makes sense to keep these methods in sync. If a strict comparison for unique was to be introduced, which I am personally not against, you could update this as well to match.

This illustrates the considerations you have to make when comparing eloquent models...

$userA = User::find(1);
$userA->someAttribute = 'hello';

$userB = User::find(1);
$userB->someAttribute = 'world';


$userA->getKey() === $userB->getKey(); // true

$userA->is($userB); // true

$userA == $userB; // false

$userA === $userB; // false

[taylorotwell]

So is this ready to merge or you are still unsure regarding the things you mentioned above?

[timacdonald]

I’m happy with it as is @taylorotwell

I think any strict / loose comparison change is a different conversation / PR which would target 5.9 as it would change existing behaviour for the unique method as well.