title: Symfony - Validate if the values are not repeated in a combobox form
body: <p>I have a form with a combobox and when submited the points values can not be repeated</p>
  
  <p>The form</p>
  
  <pre><code>-&gt;add('points', 'choice', array(
                      'attr' =&gt; array('class' =&gt; 'form-control m-b'),
                      'choices' =&gt; array(
                          '0' =&gt; '0',
                          '1' =&gt; '1',
                          '2' =&gt; '2',
                          '3' =&gt; '3',
                          '4' =&gt; '4',
                          '5' =&gt; '5',
                          '6' =&gt; '6',
                          '7' =&gt; '7',
                          '8' =&gt; '8',
                          '9' =&gt; '9',
                          '10' =&gt; '10',
                      )
                  ))
  </code></pre>
  
  <p>the version of symfony is 2.6</p>
  
  <p>Any help will be appreciated</p>