title: Method "xxx" targeted by Callback constraint does not exist Symfony2
body: <p>This method is inside my Entity class </p>
  
  <pre><code>public function validateStartDate(ExecutionContextInterface $context)
  {
      if ($this-&gt;getEndDate() &lt; $this-&gt;getStartDate()){
        $context-&gt;addViolationAt(
            'endDate',
            'End date cannnot be before Start date',
            array(),
            null
        );
      }
  
  }
  </code></pre>
  
  <p>and im using a callback constraint on $startDate</p>
  
  <pre><code>/**
   * @ORM\Column(type="datetime", name="start_date")
   * @Assert\Type("\DateTime")
   * @Assert\Callback(methods={"validateStartDate"})
   */
  private $startDate;
  </code></pre>
  
  <p>I have the following imports </p>
  
  <pre><code>use Symfony\Component\Validator\Constraints as Assert;
  use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
  use Symfony\Component\Validator\ExecutionContextInterface;
  use Symfony\Component\Validator\ExecutionContext;
  use Doctrine\Common\Collections\ArrayCollection;
  use Doctrine\ORM\Mapping as ORM;
  </code></pre>
  
  <p>Using Symfony 2.5 with mysql.</p>
  
  <p>The error i get when I submit my form is </p>
  
  <blockquote>
    <p>Method "validateStartDate" targeted by Callback constraint does not
    exist</p>
  </blockquote>
  
  <p>Any help in this regard will be much appreciated. </p>
  
  <p>Thanks in advance</p>