title: Array to string conversion error with choice form type
body: <h2>What I'm trying to do :</h2>
  
  <p>I have a database with a table "teams" and a property "weekday". I generated my doctrine entity and now I'm building a Symfony2 form. </p>
  
  <p>I'd like to save an array with weekdays into my weekdays property in the teams table. The weekdays property is a VARCHAR(255) so it should be able to contain a string array. I use the choice type, <strong>but I get an array to string conversion error when submitting the form</strong>. </p>
  
  <h2>What I'm doing:</h2>
  
  <p>I used the Symfony2 choice formtype (with the multiple option), because a team can select a couple of weekdays when they're available. I first retrieved my team object data. Then I make the form like this:</p>
  
  <pre><code>$builder = $this-&gt;createFormBuilder($team);
  $form = $builder-&gt;add('weekday', 'choice', array(
          'choices' =&gt; array(
              'mon'    =&gt; 'Monday',
              'tue'    =&gt; 'Tuesday',
              'wed'    =&gt; 'Wednesday',
              'thu'    =&gt; 'Thursday',
              'fri'    =&gt; 'Friday',
              'sat'    =&gt; 'Saturday',
              'sun'    =&gt; 'Sunday',
              ),
          'multiple' =&gt; true,
          'expanded' =&gt; true,
          'label' =&gt; 'Day of the week',
          'label_attr' =&gt; array('class' =&gt; 'control-label'),
          'attr' =&gt; array('placeholder' =&gt; 'Day of the week', 'size' =&gt; '7')
          ))-&gt;getForm();
  </code></pre>
  
  <p>When the form is submitted, I save the changes to the db with the entity manager:</p>
  
  <pre><code>if ($request-&gt;isMethod('POST')) {
      $form-&gt;bind($request);
  
      if ($form-&gt;isValid()) {
  
          // Save changes to db
          $em = $this-&gt;getDoctrine()-&gt;getManager();
          $em-&gt;persist($team);
          $em-&gt;flush();
  
          // Redirect to new canonical url
          return $this-&gt;redirect($this-&gt;generateUrl('team_edit', array('nameCanonical' =&gt; $team-&gt;getNameCanonical(), 'code' =&gt; $team-&gt;getCode())));
      }
  </code></pre>
  
  <h2>Error:</h2>
  
  <p>This all seems 100% valid code to me. I've made other forms in symfony2 like this. But when I choose one or multiple weekdays in the form, and then submit, I get this error:</p>
  
  <blockquote>
    <p>An exception occurred while executing 'UPDATE teams SET weekday = ?
    WHERE id = ?' with params {"1":["mon","tue","wed"],"2":6}:</p>
    
    <p>Notice: Array to string conversion in
    /Users/username/Dropbox/www/projectname/www/vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php
    line 1211</p>
  </blockquote>
  
  <p>(<a href="http://i.imgur.com/5J8zv.png">Full error page here</a>)</p>
  
  <p>I can't think of a way to fix this. Help appreciated!
  My full code is viewable <a href="https://gist.github.com/4434897">on this gist</a>.</p>