title: Yii validation rules for foreign key
body: <p>Let's say I have an ActiveRecord with the following validation rules:</p>
  
  <pre><code>public function rules() {
      return array(
          array('model', 'required'),
          // ....
          array('model', 'exist',
              'allowEmpty' =&gt; false,
              'attributeName' =&gt; 'id',
              'className' =&gt; 'Model',
              'message' =&gt; 'The specified model does not exist.'
          )
      );
  }
  </code></pre>
  
  <p>The first rule forces the <code>model</code> field not to be blank, the second one checks it has a consistent value (<code>model</code> is a foreign key).</p>
  
  <p>If I try to validate a form in which I leave empty the field <code>model</code> I get 2 errors, one for  the first rule and one for the second rule.</p>
  
  <p>I would like to receive only the "<em>cannot be blank</em>" error message.</p>
  
  <p>Is there a way to stop the validation when the first rule is not satisfied? </p>