Laravel 5 Querying with relations causes "Call to a member function addEagerConstraints() on null" error

Question

I have been trying to create a simple user management system but keep on hitting road blocks when it comes to querying relations. For example I have users and roles and whenever I try to make a query for all users and their roles I get an error. The one in the title is only the latest one I've encountered.

My User and Role Models look like this:

class Role extends Model
{
    public function users()
    {
        $this->belongsToMany('\App\User', 'fk_role_user', 'role_id', 'user_id');
    }
}

---

class User extends Model
{
    public function roles()
    {
        $this->belongsToMany('\App\Role', 'fk_user_role', 'user_id', 'role_id');
    }
}

My migration table for many-to-many relationship between the two looks like this:

public function up()
    {
        Schema::create('role_user', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('user_id')->unsigned()->nullable(); //fk => users
            $table->integer('role_id')->unsigned()->nullable(); //fk => roles

            $table->foreign('fk_user_role')->references('id')->on('users')->onDelete('cascade');
            $table->foreign('fk_role_user')->references('id')->on('roles')->onDelete('cascade');
        });
    }

And then I try to get all records with their relation in a controller:

public function index()
{
    $users = User::with('roles')->get();

    return $users;
}

So I need another pair of eyes to tell me what is it I am missing here?

Answer 1

You are missing return statements in the methods that define relations. They need to return relation definition.

Replace

public function roles()
{
    $this->belongsToMany('\App\Role', 'fk_user_role', 'user_id', 'role_id');
}

With

public function roles()
{
    return $this->belongsToMany('\App\Role', 'role_user', 'user_id', 'role_id');
}