[6.x] Add existsOr and doesntExistOr to the querybuilder

[SjorsO]

Resubmit of #30479

In my controllers, I often use something like this to validate requests:

$hasOpenDossier = $user->dossiers()
    ->whereNull('closed_at')
    ->exists();

if ($hasOpenDossier) {
    abort(422, 'User already has an open dossier');
}

With this PR, I can do this instead:

$user->dossiers()
    ->whereNull('closed_at')
    ->doesntExistOr(function () {
        abort(422, 'User already has an open dossier');
    });

This way I don't have to create a temporary variable, and the code is more logically grouped together (which is especially nice in more complex projects where you can have three of these checks in a row).

I would almost always use this feature for aborting. It could also be used for other things, but to be honest I can't really think of any. (maybe adding a doesntExistOrAbort macro to my projects would be a better solution).

---

An alternative to adding two new methods is adding an optional $callback argument to the exists() and doesntExist() methods. I think adding two new methods is a cleaner way of doing it, mainly because it keeps the parameters and return type of exists() and doesntExist() simple.

[driesvints]

@SjorsO can you rebase with the 6.x branch? StyleCI updated their default checks today. Rebasing should make the checks pass again.

[chuckrincon]

@SjorsO It's possible to use the null coalescing operator (??), produces the same return

// Before
return $this->exists() ? true : $callback();

// After
return $this->exists() ?? $callback();

[SjorsO]

@SjorsO It's possible to use the null coalescing operator (??), produces the same return

// Before
return $this->exists() ? true : $callback();

// After
return $this->exists() ?? $callback();

?? will only call the callback if exists is null or not set, which is never the case.

I think you're thinking about ?:, which would be slightly shorter than the current code. But i prefer not being fancy and just using a simple shorthand if statement.

[netpok]

I'm not sure about this,
one can already use the:

abort_if(
    $user->dossiers()->whereNull('closed_at')->exists(),
    422, 'User already has an open dossier'
);

method which is way more expressive.

The findOr method is used to provide a default when the record not exists, but I don't see a use-case when one want to do that with an exists() to use the return value and the …->exists() ?: randomStatement is not enough.

---

Little unrelated but I think one should not throw 422 errors manually if the controller already has validation it can be solved with a nice rule or an after callback

[SjorsO]

Queries often don't fit neatly on a single line, in that case you can't use abort_if like that

[netpok]

I would argue than it probably should be moved to a method or better to the FormRequest object, but that's not in the scope of this pull request.

I consider these methods in the same category than the findBy methods (#30442).

---

Also this works too:

$user->dossiers()
    ->whereNull('closed_at')
    ->doesntExist() ?: abort(422, 'User already has an open dossier');

[netpok]

I think it would be better to typehint Closure|bool

[netpok]

Allow all types here (should only be closure and bool, but there is some time till union types will be available).

[netpok]

And return $this->exists() ?: value($callback)

I prefer ?: over ? true : but maybe that's just me.

[s51983]

When Model use SoftDeletes, existsOr / doesntExistOr didn't check deleted_at columns

 User::where('id', $id)->exists();

SQL: select exists(select * from `users` where `id` = ? and `users`.`deleted_at` is null) as `exists`

 User::where('id', $id)->existsOr(function(){
    abort(404,'User not exists!')
});

SQL: select exists(select * from `users` where `id` = ?) as `exists`

How to fix it?