title: Single ID is not allowed on composite primary key in entity
body: <p>I'm creating an API REST using the API Platform framework. I have an entity with a composite primary key. </p>
  
  <p>I'm getting this error when sending a get request on the table <code>Umlfiles_Properties</code>:</p>
  
  <blockquote>
    <p>Single id is not allowed on composite primary key in entity AppBundle\Entity\Umlfiles_Properties</p>
  </blockquote>
  
  <p>The code bellow is the <code>Umlfiles_Properties</code> entity code.</p>
  
  <pre><code>/**
  * Umlfiles_Properties
  *
  * @ApiResource
  * @ORM\Table(name="umlfiles_properties")
  * @ORM\Entity(repositoryClass="AppBundle\Repository\Umlfiles_PropertiesRepository")
  */
  class Umlfiles_Properties
  {
  /**
   * @var int
   *
   * @ORM\Column(name="umlfile_id", type="integer")
   * @ORM\Id
   * @ORM\ManyToOne(targetEntity="Umlfiles", inversedBy="id")
   */
  private $umlfile_id;
  
  /**
   * @var int
   *
   * @ORM\Column(name="property_id", type="integer")
   * @ORM\Id
   * @ORM\ManyToOne(targetEntity="Property", inversedBy="id")
   */
  private $property_id;
  
  /**
   * @var array
   *
   * @ORM\Column(name="value", type="array")
   */
  private $value;
  
  
  
  /**
   * Set umlfileId.
   *
   * @param int $umlfileId
   *
   * @return Umlfiles_Properties
   */
  public function setUmlfileId($umlfileId)
  {
      $this-&gt;umlfile_id = $umlfileId;
  
      return $this;
  }
  
  /**
   * Get umlfileId.
   *
   * @return int
   */
  public function getUmlfileId()
  {
      return $this-&gt;umlfile_id;
  }
  
  /**
   * Set propertyId.
   *
   * @param int $propertyId
   *
   * @return Umlfiles_Properties
   */
  public function setPropertyId($propertyId)
  {
      $this-&gt;property_id = $propertyId;
  
      return $this;
  }
  
  /**
   * Get propertyId.
   *
   * @return int
   */
  public function getPropertyId()
  {
      return $this-&gt;property_id;
  }
  
  /**
   * Set value.
   *
   * @param array $value
   *
   * @return Umlfiles_Properties
   */
  public function setValue($value)
  {
      $this-&gt;value = $value;
  
      return $this;
  }
  
  /**
   * Get value.
   *
   * @return array
   */
  public function getValue()
  {
      return $this-&gt;value;
  }
  }
  </code></pre>