PHP Exchange::participants示例

 public function postLeave(Exchange $exchange)
 {
     if ($exchange->processed) {
         return Redirect::route('exchange', ['exchange' => $exchange->slug])->withErrors(['e' => 'You can\'t delete a processed exchange']);
     }
     if ($exchange->initiator->id == Auth::User()->id) {
         return Redirect::route('exchange', ['exchange' => $exchange->slug])->withErrors(['e' => 'You can\'t leave an exchange you created']);
     }
     $rules = array('' => '');
     $validator = Validator::make(Input::all(), $rules);
     if ($validator->fails()) {
         return Redirect::route('exchange.leave')->withErrors($validator)->withInput(Input::all());
     } else {
         $user = $exchange->participants()->whereUsername(Auth::User()->username)->count();
         if ($user != 0) {
             $exchange->participants()->detach(Auth::User());
         } else {
             return Redirect::route('exchange', ['exchange' => $exchange->slug])->withErrors(['e' => 'You aren\'t in this exchange']);
         }
         return Redirect::route('home');
     }
 }