在你的模型中你有 protected $primaryKey='city_id'; 但在你看来你有:

In your model you have protected $primaryKey='city_id'; but in your view you have:

{{ Form::model($city,array('route'=>array('admin.cities.update',$city->id),'method'=>'PUT','files'=>true)) }}

我的意思是 $city->id 应该是 $city->city_id

I mean $city->id should be $city->city_id