title: No identifier/primary key specified for Entity (...) Every Entity must have and identifier/primary key
body: <p>I have <code>Peticion</code> entity but something is missing because appears the following error:</p>
  
  <pre><code>No identifier/primary key specified for Entity (...) Every Entity must have and identifier/primary key
  </code></pre>
  
  <p>This is the entity code:</p>
  
  <pre><code>&lt;?php
  
  namespace Project\UsuarioBundle\Entity;
  
  use Doctrine\ORM\Mapping as ORM;
  
  /**
   * Peticion
   *
   * @ORM\Table(name="peticion")
   * @ORM\Entity
   */
  class Peticion
  {
      /**
       *
       * @ORM\Id
       * @ORM\ManyToMany(targetEntity="Project\UsuarioBundle\Entity\Usuario", inversedBy="usuNick2")
       * @ORM\JoinTable(name="USUARIO",
       *      joinColumns={@ORM\JoinColumn(name="USU_NICK_1", referencedColumnName="USU_NICK")},
       *      inverseJoinColumns={@ORM\JoinColumn(name="USU_NICK_2", referencedColumnName="USU_NICK")}
       *      )
       */
      private $usuNick1;
  
      /**
       *
       * @ORM\Id
       * @ORM\ManyToMany(targetEntity="Project\UsuarioBundle\Entity\Usuario", mappedBy="usuNick1"))
       */
      private $usuNick2;
  
      /**
       * @var \DateTime
       *
       * @ORM\Column(name="PET_FECHA", type="date", nullable=false)
       */
      private $fecha;
  </code></pre>