title: Return Symfony Form submitted data as string, not array
body: <p>I use Symfony 2.7.</p>
  
  <p>Is it possible to get submitted data as string, not as array?</p>
  
  <p>I have a custom form type for searching through records and I want it to have specific output. I want to use GET method on the form, so submitted data could be displayed and used in the querystring right away, without additional redirect:</p>
  
  <p>Form is named <em>search</em> and has fields like
  - firstName (text)
  - lastName (text)
  ...</p>
  
  <p>And if submit the form, I want the result NOT to be</p>
  
  <pre><code>search =&gt; array(
     firstName =&gt; 'John',
     lastName =&gt; 'Doe',
  )
  </code></pre>
  
  <p>But I need it to look like</p>
  
  <pre><code>search =&gt; 'firstName:John lastName:Doe'
  </code></pre>
  
  <p>I tried to use data transformers for this, but no luck so far. Is it possible and how?</p>
  
  <p><strong>form build</strong> I am using right now:</p>
  
  <pre><code>    $builder
          -&gt;add('firstname')
          -&gt;add('lastname')
          -&gt;add('submit', 'submit')
      ;
  
      $builder-&gt;addModelTransformer(new CallbackTransformer(
          function($origData){
              return $origData; //no need to set form fields for me
          },
          function($submitData){
              $q = QueryResolver::buildQuery($submitData);
              return $q;
          }
      ));
  </code></pre>
  
  <p>The 'q' variable in second callback then really is </p>
  
  <pre><code>'firstname:john lastname:doe'
  </code></pre>
  
  <p>but the Request 'search' value is still an array:</p>
  
  <pre><code>  'search' =&gt; 
        'firstname' =&gt; 'john'
        'lastname' =&gt; 'doe'
         ...
        'submit' =&gt; ''
        '_token' =&gt; 'S9k9ZBPaUVz13nNGXn8UoRarxa37IHNWU_AJZGt00H8'
  </code></pre>