title: One TextField for two attributes with DataTransformer
body: <p>I have searched a lot on google but I have no idea of how to solve my problem.
  I have an Entity <code>EntreeListe</code> which contains two attributes <code>rayon</code> and <code>produit</code>. I would like that the user enter in a text field : <code>Rayon : Produit</code>.</p>
  
  <p>So, I add two DataTransformer on my textfield <code>produit</code></p>
  
  <pre><code>$builder-&gt;get('produit')
      -&gt;addModelTransformer(new StringToProduitTransformer($this-&gt;manager));
  $builder-&gt;get('produit')
      -&gt;addModelTransformer(new StringToRayonTransformer($this-&gt;manager));
  </code></pre>
  
  <p>So that I can transform <code>explode(' : ', $string)[0]</code> into a <code>Rayon</code> and <code>explode(' : ', $string)[1]</code> into a <code>Produit</code>.</p>
  
  <p>The problem is that, when I submit the form, the parameter passed to <code>reverseTransform</code> of <code>StringToProduitTransformer</code> is not a string but a <code>Rayon</code> because the transformation of <code>StringToRayonTransformer</code> is already done.</p>
  
  <p>I don't know if I'm clear, so just ask questions. Any suggestions is welcome :).</p>
  
  <p>What I want is to have the string passed to the two reverseTransform... So have multiple DataTransformer for one field.</p>
  
  <p>Or is there another way to do this ? To complete two attributes with one input ?</p>
  
  <p>Thank you very much.</p>