title: Laravel ORM relationship method 'BelongsToMany' throwing error
body: <p><strong>Summary</strong></p>
  
  <p>I am receiving the following error when trying to call the relationship:</p>
  
  <blockquote>
    <p>Object of class Illuminate\Database\Eloquent\Relations\BelongsToMany
    could not be converted to string</p>
  </blockquote>
  
  <p>My setup is very basic, and consists of two models, <code>User</code> and <code>Role</code>. </p>
  
  <p><strong>User Model [User.php]</strong></p>
  
  <pre><code>&lt;?php
  use Illuminate\Auth\UserInterface;
  
  class User extends Eloquent implements UserInterface {
  
      protected $table = 'users';
      protected $hidden = array('password');
      protected $fillable = array('id', 'username', 'password');
  
  
      public function getAuthIdentifier() {
          return $this-&gt;getKey();
      }
  
      public function getAuthPassword() {
          return $this-&gt;password;
      }
  }
  </code></pre>
  
  <p><strong>Role Model [Role.php]</strong></p>
  
  <pre><code>&lt;?php
  class Role extends Eloquent {
  
      protected $table = "roles";
      protected $fillable = array(
          'id',           
          'code',
          'name'
      );
  
      public function foo() {
          return $this-&gt;belongsToMany('User', 'map_role_user', 'role_id', 'user_id');
      }
  }
  </code></pre>
  
  <p>And finally I'm calling the method <code>foo</code> in the routes file, example:</p>
  
  <pre><code>Route::get('role', function() {
          return Role::find(1)-&gt;foo();  
      });
  </code></pre>