Move model to a trait

[GromNaN]

Fix #2120
Fix #2445
Fix #2991

By moving all the logic to a trait, it makes it possible to reuse entities provided by community projects. Example: https://github.com/z-song/laravel-admin/blob/master/src/Auth/Database/Administrator.php

The properties $primaryKey and $keyType can't be in the trait because PHP forbid declaring a property in a trait that is different (type and value) than the property declared in the parent class.

For Laravel's User model:

namespace App\Models;

use Illuminate\Foundation\Auth\User as Authenticatable;
use MongoDB\Laravel\Eloquent\DocumentModel;

class User extends Authenticatable
{
    protected $connection = 'mongodb';
    protected $collection = 'users';
    protected $primaryKey = '_id';
    protected $keyType = 'string';
}

For Laravel Sanctum (with default model override):

namespace App\Models;

use Laravel\Sanctum\PersonalAccessToken as SanctumToken;
use MongoDB\Laravel\Eloquent\DocumentModel;

class PersonalAccessToken extends SanctumToken
{
    use DocumentModel;

    protected $connection = 'mongodb';
    protected $collection = 'personal_access_tokens';
    protected $primaryKey = '_id';
    protected $keyType = 'string';
}

I have mixed feelings about this change, as it breaks the link with the overloaded parent methods. It would probably be better to make the change in each community-package when necessary.

[GromNaN]

Currently, the Model class is a marker for MongoDB models. If a trait is used, an other marker will be necessary.
https://github.com/mongodb-php/laravel-mongodb/blob/f06f7b3dca88cfd5cc6a823ff01051b4a46ca10a/src/Eloquent/HybridRelations.php#L145

[GromNaN]

The trait DocumentModel is extracted from the MongoDB\Laravel\Eloquent\Model class, the only changes are commented.

[GromNaN]

When the trait is used, the properties $keyType and $primaryKey must be defined, because they can't be redefined by the trait.

[GromNaN]

This property is not defined in the trait, otherwise it's allowed to redefine in the class that uses the trait.

[GromNaN]

Changing the visibility to private. There is a getter and an setter for this method. It doesn't need to be protected. Since it's a trait, it can still be accessed directly in a class that uses the trait.

[GromNaN]

This method replaces $class instanceof MongoDB\Laravel\Eloquent\Model to check if the model class is for a MongoDB connection. It is public and can be used in projects.

[GromNaN]

All the test models have been updated to use the trait, so that we are sure all the features works without extending MongoDB\Laravel\Eloquent\Model.

[alcaeus]

Having one test with a model that extends our document model class instead of using the trait will help us prevent regressions in our model class.

[alcaeus]

class_uses_recursive looks like it has significant performance implications. Using a marker interface and checking using is_subclass_of would probably be more efficient.

Alternatively, checking whether the class is a subclass of this model class first, and only checking for traits in other cases would probably solve the performance issue for most cases.

[GromNaN]

Added a shortcut to check our Model class + a memory cache for when the same class is checked twice in the same request.

[GromNaN]

This class continues to extend MongoDB\Laravel\Eloquent\Model

[masterbater]

@GromNaN Hopefully in documentation can add a guide for third party packages like spatie's laravel-permissions, bouncer, tenancy etc, sanctum, etc. Or create a community for laravel packages being modified to work with laravel mongodb. This way all popular packages will have counterpart that is made to work with mongodb thanks.

[GromNaN]

@masterbater The documentation is going to be written by MongoDB's doc team.