title: How to use translatable fields in Sonata Admin?
body: <p>I use "Knp Doctrine2 Behaviors" for entity translations and "A2LiX Translation Form" to translate entities in Sonata Admin form. Everything work fine. But I can’t realize what I should put in "configureDatagridFilters"  and "configureListFields"  methods of Admin class? </p>
  
  <p>Naturally, for example, $datagridMapper->add('title'); doesn’t work because it is  translatable field of my "Post" entity, and it is located in PostTranslation class, but Admin class is for Post entity.  The __call method in Post entity doesn’t help, it seems it doesn’t work in admin class. </p>
  
  <p>$datagridMapper->add('translations.title'); doesn't cause errors and there is row with entity, but there is nothing between <code>&lt;a&gt; &lt;/a&gt;</code> tags:</p>
  
  <p><a href="https://i.stack.imgur.com/V3a6n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/V3a6n.png" alt="enter image description here"></a></p>
  
  <p>Just in case, here is my Post, PostTranslation and PostAdmin classes: </p>
  
  <pre><code>/**
   * Blog post
   *
   * @ORM\Table(name="post")
   * @ORM\Entity(repositoryClass="AppBundle\Repository\PostRepository")
   */
  class Post
  {
      use ORMBehaviors\Translatable\Translatable;
  
      public function __call($method, $arguments)
      {
          return $this-&gt;proxyCurrentLocaleTranslation($method, $arguments);
      }
  
      /**
       * @var integer
       *
       * @ORM\Column(name="id", type="integer")
       * @ORM\Id
       * @ORM\GeneratedValue(strategy="AUTO")
       */
      private $id;
  
  
      /**
       * @ORM\ManyToOne(targetEntity="Category", inversedBy="posts", fetch="EAGER")
       * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
       */
      private $category;
  
  
      public function __construct() {}
  
      /**
       * Get id
       *
       * @return integer
       */
      public function getId()
      {
          return $this-&gt;id;
      }
  
  
      public function setCategory(Category $category)
      {
          $category-&gt;addPost($this);
          $this-&gt;category = $category;
      }
  
      public function getCategory()
      {
          return $this-&gt;category;
      }
  } 
  
  /**
   * Post Translation
   * 
   * @ORM\Entity
   */
  class PostTranslation
  {
  
      use ORMBehaviors\Translatable\Translation;
  
      /**
       * @var string
       *
       * @ORM\Column(name="title", type="string", length=255)
       */
      private $title;
  
      /**
       * @var string
       *
       * @ORM\Column(name="content", type="string", length=255)
       */
      private $content;
  
      public function __construct() {}
  
      /**
       * Set title
       *
       * @param string $title
       *
       * @return post
       */
      public function setTitle($title)
      {
          $this-&gt;title = $title;
  
          return $this;
      }
  
      /**
       * Get title
       *
       * @return string
       */
      public function getTitle()
      {
          return $this-&gt;title;
      }
  
      public function setContent($content)
      {
          $this-&gt;content = $content;
      }
  
      public function getContent()
      {
          return $this-&gt;content;
      }
  
  }
  
  /**
   * Class PostAdmin
   */
  class PostAdmin extends Admin
  {
      protected function configureFormFields(FormMapper $formMapper)
      {
          $formMapper
              -&gt;add('translations', 'a2lix_translations')
              -&gt;add('category', 'entity', [
                  'class' =&gt; 'AppBundle\Entity\Category',
                  'property' =&gt; 'name'
              ])
          ;
      }
  
      protected function configureDatagridFilters(DatagridMapper $datagridMapper)
      {
          $datagridMapper-&gt;add('translations.title');
      }
  
      protected function configureListFields(ListMapper $listMapper)
      {
          $listMapper-&gt;addIdentifier('translations.title');
      }
  
  }
  </code></pre>