title: PHP form submit updates the field pip_date everytime form is submitted after editing a user
body: <p>When for a user <code>$_POST['on_pip']</code> has value equals to <code>1</code>
  it should add the current time in db by the following code :</p>
  
  <pre><code>// It will save the date when a user is rated PIP and removes the date when PIP rating gets removed
  
  if ($_POST['on_pip'] == '1'){
      $_POST['pip_date'] = $this-&gt;date-&gt;now();
  } else {
      $_POST['pip_date'] = null;
  }
  
  $this-&gt;Model_User-&gt;save(_request('user_id'), $_POST)
  </code></pre>
  
  <p>(I am using <code>radio button</code> here if it says yes it saves <code>value = 1</code> and if its no <code>value = 0</code>)</p>
  
  <p><strong>My Problem :</strong></p>
  
  <p>Suppose a user have <code>on_pip</code> value saved equals to 1. when I edit that user with on_pip value 1 and update some other details and save the user, it updates the pip_date for current time.</p>
  
  <p>How can I check if value of $_POST['on_pip'] was changed on the form submit or not? </p>
  
  <p>If a user already have on_pip value it should not update the pip_date</p>