Inheritance: extends Illuminate\Database\Eloquent\Model
 public function addRel($blog_id, $role_id)
 {
     Laralum::permissionToAccess('laralum.blogs.access');
     $rel = Blog_Role::whereBlog_idAndRole_id($blog_id, $role_id)->first();
     if (!$rel) {
         $rel = new Blog_Role();
         $rel->blog_id = $blog_id;
         $rel->role_id = $role_id;
         $rel->save();
     }
 }