Global select list not respected in belongsToMany relationship

[KKSzymanowski]

• Laravel Version: 5.5.24
• PHP Version: 7.1.11
• Database Driver & Version: MySQL 15.1 Distrib 10.2.10-MariaDB

Description:

I'm working with a legacy database with an enormous number of columns in tables and I want to fetch only few of them. Usually I restrict the column list globally by adding a query scope in the boot method of the model and it works fine with one-to-many relationships but with a many-to-many relationship all columns from the related table are being fetched.

This is because the scopes are applied after the column list on the query instance is checked in BelongsToMany::get()

public function get($columns = ['*'])
{
    $columns = $this->query->getQuery()->columns ? [] : $columns;

    $builder = $this->query->applyScopes();

    // ...
}

Is there a reason behind this? Can this order be reversed like so:

public function get($columns = ['*'])
{
    $builder = $this->query->applyScopes();

    $columns = $builder->getQuery()->columns ? [] : $columns;

    // ...
}

[Dylan-DPC-zz]

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[KKSzymanowski]

I believe it is a bug, because the scope treatment is inconsistent across relationship.
Edit: To be precise, the scope treatment is quite the same, just for BelongsToMany the scopes are applied too late, rendering them useless in particular cases.

Here are steps needed to reproduce, so you have a full bug report:

Steps to reproduce

1. Create a User model

class User extends Authenticatable
{
    protected $fillable = ['name'];

    public function permissions()
    {
        return $this->belongsToMany(Permission::class);
    }
}

2. Create a Permission model

class Permission extends Model
{
    public static function boot()
    {
        parent::boot();

        static::addGlobalScope(function(Builder $query) {
            $query->select('name');
        });
    }
}

3. Create migrations for the models and the intermediary table:

Schema::create('users', function (Blueprint $table) {
    $table->increments('id');
    $table->string('name');
    $table->timestamps();
});
Schema::create('permissions', function (Blueprint $table) {
    $table->increments('id');
    $table->string('name');
    $table->text('description');
    $table->timestamps();
});
Schema::create('permission_user', function (Blueprint $table) {
    $table->increments('id');
    $table->integer('permission_id');
    $table->integer('user_id');
});

4. Migrate the database
5. Create a user

\App\User::create([
    'name' => 'John Doe',
]);

6. Create a test route:

Route::get('/', function () {
    $user = \App\User::first();

    DB::listen(function ($query) {
        dump($query->sql);
    });

    $user->permissions()->get();
});

What is expected

Only the name column should be fetched from the permissions table and the dumped query
should look something like this:

select 
    `name`, 
    `permission_user`.`user_id` as `pivot_user_id`, 
    `permission_user`.`permission_id` as `pivot_permission_id` 
from `permissions` 
inner join `permission_user` on `permissions`.`id` = `permission_user`.`permission_id` 
where `permission_user`.`user_id` = ? 

What is actually happening

All columns are fetched from the permissions table and the query looks like this:

select 
    `name`, 
    `permissions`.*, 
    `permission_user`.`user_id` as `pivot_user_id`, 
    `permission_user`.`permission_id` as `pivot_permission_id` 
from `permissions` 
inner join `permission_user` on `permissions`.`id` = `permission_user`.`permission_id` 
where `permission_user`.`user_id` = ?