title: Disable validation in update form - CakePHP
body: <p>I have a form that i use to register and update data.
  It works fine, but when i update the data, the model validation returns false, because the value inserted already exists.</p>
  
  <p>I have the following code:</p>
  
  <pre><code>/* Validation Rule*/
  public $validate = array(
      'unique' =&gt; array(
          'rule' =&gt; array('unique', 'field in the table'),
          'message' =&gt; 'The field cannot be empty.'
      )
      ...
  )
  /* Function that check if the value already exists */
  public function unique($value, $field) {
      $check = $this-&gt;find('count', array(
          'recursive' =&gt; -1,
          'conditions' =&gt; array(
              $this-&gt;Alias.$field =&gt; $value
          )
      ));
  
      return $check == 0;
  }
  </code></pre>
  
  <p>So, how can i disable the unique rule, but keeping the other rules?</p>