User::exists() overrides Builder::exists() leading to unexpected behavior

[alexweissman]

We implement a User::exists($value, $identifier = 'user_name', $checkDeleted = true), which overrides the base exists method in Builder.

This can lead to confusion though, because the signatures of the two methods are different, and they operate on different assumptions. User::exists is implicitly generating a where query, whereas Builder::exists simply determines whether or not the current query returns any results.

The fix for this would be to rename User::exists to something else. We could also implement this at the level of Model, rather than just for the User class.

[alexweissman]

Ok, I've addressed this in v4.1.7 (e5f5487) by deprecating the User::exists method and replacing it with the findUnique method for all models. We can't get rid of User::exists right away as some people may be depending on it.