Why does the Doctrine getter method return null for the ID?

Question

I use the auto-generated getters in a class table inheritance setup in a Symfony project. getId() returns null, while every other getter works. Can you spot any problem? What should I search for? I imported the database entries manually, but I don't think that is the cause.

The abstract parent entity

//src/Acme/WebzineBundle/Entity/Content.php
namespace Acme\WebzineBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Content
 *
 * @ORM\Table()
 * @ORM\Entity
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="heading", type="integer")
 * @ORM\DiscriminatorMap({
 *   0 = "Review"
 * })
 */
abstract class Content
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var \DateTime
     *
     * @ORM\Column(name="edited", type="date")
     */
    private $edited;


    /**
     * Get id
     *
     * @return integer 
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Get edited
     *
     * @return \DateTime 
     */
    public function getEdited()
    {
        return $this->edited;
    }
}

The child entity

//src/Acme/WebzineBundle/Entity/Review.php
namespace Acme\WebzineBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Review articles
 *
 * @ORM\Table()
 * @ORM\Entity
 */
class Review extends Content
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var string
     *
     * @ORM\Column(name="title", type="string", length=127)
     */
    private $title;


    /**
     * Get id
     *
     * @return integer 
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Get title
     *
     * @return string 
     */
    public function getTitle()
    {
        return $this->title;
    }
}

The next foreign key constraint is on the table of the child entity:

CONSTRAINT `FK_7EEF84F0BF396750` FOREIGN KEY (`id`) REFERENCES `Content` (`id`)
ON DELETE CASCADE

The query

//src/Acme/AdminBundle/Controller/MainController.php
namespace Acme\AdminBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class MainController extends Controller
{
    public function indexAction(Request $request)
    {
        $em = $this->getDoctrine()->getManager();
        $query = $em->createQuery(
            'SELECT post FROM AcmeWebzineBundle:Content post
             ORDER BY post.edited DESC'
        );
        $query->setMaxResults(30);

        $posts = $query->getResult();
        $latest_post = $posts[0];

        return $this->render('AcmeAdminBundle:Main:index.html.twig', array(
            'posts' => $posts,
            'id' => gettype($latest_post->getId()), // This returns null!
            'edited' => $latest_post->getEdited(),  // Any other getter works
            'title' => $latest_post->getTitle(),    // also from the child entity.
        ));
    }
}

Answer 1

You need to remove the id property and getId() method from the child class

//src/Acme/WebzineBundle/Entity/Review.php
namespace Acme\WebzineBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Review articles
 *
 * @ORM\Table()
 * @ORM\Entity
 */
class Review extends Content
{ 
    /**
     * @var string
     *
     * @ORM\Column(name="title", type="string", length=127)
     */
    private $title;


    /**
     * Get title
     *
     * @return string 
     */
    public function getTitle()
    {
        return $this->title;
    }
}

You can not create object of Content class.

And better use only unique properties and methods in Review class, because others are inherited from abstract Content class.