title: ZF2 Doctrine 2 ObjectSelect with distinct on field
body: <p>to populate my form I use the fieldset approach. For one given form field I will use a select and the options are coming directly from an entity like this:</p>
  
  <pre><code>$this-&gt;add(
              array(
                  'type' =&gt; 'DoctrineModule\Form\Element\ObjectSelect',
                  'name' =&gt; 'city',
                  'options' =&gt; array(
                      'label' =&gt; 'City: ',
                      'object_manager' =&gt; $this-&gt;_om,
                      'target_class' =&gt; 'Hotbed\Entity\AllAdresses',
                      'property' =&gt; 'city',
                      'is_method' =&gt; true,
                      'find_method' =&gt; array(
                          'name' =&gt; 'findBy',
                          'params' =&gt; array(
                              'criteria' =&gt; array('postal_code' =&gt; $postalCode),
                              'orderBy' =&gt; array('city' =&gt; 'ASC'),
                          ),
                      ),
                  ),
                  'attributes' =&gt; array(
                      'class' =&gt; 'form-control input-large',
                      'required' =&gt; '*'
                  ),
              )
      );
  </code></pre>
  
  <p>This works pretty well. The only inconvient is that I have to put a distinct on the field city. How can I solve this problem?
  Regards Andrea</p>