Eloquent Custom Casts fire database queries on each save()

[aymericauberger]

• Laravel Version: 7.x
• PHP Version: 7.4.3

Description:

When using an Eloquent custom cast on a model, if the value has been retrieved but not changed and we hit the save() method, a database query will be fired to re-insert the value and update the timestamps.

I believe this is because the originalIsEquivalent method on the Illuminate\Database\Eloquent\Concerns\HasAttributes trait does not support custom casts and will always return false.

Steps To Reproduce:

Assuming we have a custom cast on the address property of the User model:

$user = User::first();
if ($user->address) {
  // Nothing changed...
}
$user->save();

Possible solution:

We could add a method to be implemented on the cast class, for instance isEquivalent($attribute, $original), to determine if the value was changed or not.

[taylorotwell]

I'm going to convert this to a discussion since it is a bit of a feature request atm instead of a "bug".

[aymericauberger]

Thanks! I wasn't sure where to put this, as it isn't a bug but I was expecting it would just work like the other cast types.
I can try to submit a PR, unless someone thinks of a better solution than the one I suggested?