title: sonata admin use two entities in an admin
body: <p>im new to sonata admin, is this possible to use two entities in one admin class?  </p>
  
  <p>my User entity,</p>
  
  <p>App\MyBundle\Entity\Users.php</p>
  
  <pre><code>/**
   * @ORM\Id
   * @ORM\Column(type="integer")
   * @ORM\GeneratedValue(strategy="AUTO")
   */
  protected $id;
  
  /**
   * @var string
   *
   * @ORM\Column(name="username", type="string", length=45, nullable=true)
   */
  private $username;
  
  /**
   * @var string
   *
   * @ORM\Column(name="email", type="string", length=100, nullable=true)
   */
  private $email;
  </code></pre>
  
  <p>my UserProject entity,</p>
  
  <p>App\MyBundle\Entity\UserProjects.php</p>
  
  <pre><code>/**
   * @ORM\Id
   * @ORM\Column(type="integer")
   * @ORM\GeneratedValue(strategy="AUTO")
   */
  protected $id;
  
  /**
   * @var \User
   *
   * @ORM\ManyToOne(targetEntity="Users")
   * @ORM\JoinColumns({
   *   @ORM\JoinColumn(name="userId", referencedColumnName="id")
   * })
   */
  private $userid;
  
  /**
   * @var array
   *
   * @ORM\Column(name="projectId", type="array")
   */
  private $projects;
  </code></pre>
  
  <p>my Admin class,</p>
  
  <pre><code>class UserAdmin extends SonataUserAdmin
  {
      protected function configureFormFields(FormMapper $formMapper)
      {
           $formMapper
          -&gt;with('General') // these fields from Users Entity
              -&gt;add('username')
              -&gt;add('email')
  
           -&gt;with('Projects') // these fields from UserPrjects Entity
  
           /* here i need to add a field for projects related to current user */
        }
    }
  </code></pre>
  
  <p>is there any way to get these two entities connect together?  </p>