title: Symfony 3 Object of class could not be converted to string
body: <p>I'm have this address form. Everything is working as expected, until I added a drop down selection field for the cities. I'm getting this error when I try to save the form:</p>
  
  <blockquote>
    <p>Catchable Fatal Error: Object of class AppBundle\Entity\Address could not be converted to string</p>
  </blockquote>
  
  <p>The docs say that the EntityType field is designed to load options from a Doctrine entity.</p>
  
  <p>This is the form:</p>
  
  <pre><code> $builder
               -&gt;add('cities', EntityType::class, array(
                  'class' =&gt; \AppBundle\Entity\Cities::class,
                  'choice_label' =&gt; 'cityname',
                  'choice_value' =&gt; 'cityid')
              )
  </code></pre>
  
  <p>And this is my entity</p>
  
  <pre><code> /**
   * @var string
   * 
   * @ORM\Column(name="cities", type="string", length=55, nullable=false)
   */
  private $cities;   
  </code></pre>
  
  <p>And setters/getters:</p>
  
  <pre><code> /**
   * Set cities
   *
   * @param string $cities
   *
   * @return Address
   */
  public function setCities($cities)
  {
      $this-&gt;cities = $cities;
  
      return $this;
  }
  
  /**
   * Get cities
   *
   * @return string
   */
  public function getCities()
  {
      return $this-&gt;cities;
  }
  </code></pre>
  
  <p>I also added this:</p>
  
  <pre><code>public function __toString() {
    return $this-&gt;getCities();
  }
  </code></pre>
  
  <p>And had this result:</p>
  
  <blockquote>
    <p>Catchable Fatal Error: Method AppBundle\Entity\Address::__toString()
    must return a string value</p>
  </blockquote>