Question

Background:

In my application I have an entity that has a self referencing ManyToOne association (many children can point to a single parent). And I have a feature that does mass updates on many entities at one time using the Doctrine ORM. To keep performance from dropping dramatically due to many entities being loaded I detach entities once they’ve been updated.

Problem:

When I detach an entity that has children and later try to update any of those children Doctrine complains that it doesn’t know the parent anymore. Even if I merge the parent entity before trying to update the child.

Question:

What am I doing wrong when I detach the parent entity? I’ve tried doing cascade=”merge” and/or “detach” on the parent column and Doctrine still complains about the parent being an unknown entity when I try to persist.

I’ve mocked up a simple example that reproduces this. See below.

Test Code:

Entity\Thing.php

/**
 * @ORM\Entity()
 * @ORM\Table(name="things")
 */
class Thing
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\ManyToOne(targetEntity="Thing", inversedBy="children", cascade={"detach","merge"})
     * @ORM\JoinColumn(name="parentId", referencedColumnName="id", onDelete="SET NULL")
     */
    protected $parent;

    /**
     * @ORM\OneToMany(targetEntity="Thing", mappedBy="parent")
     */
    protected $children;

    /**
     * @ORM\Column(type="string", length=64)
     */
    protected $name;

    public function __construct($name = null)
    {
        $this->children = new ArrayCollection();
        $this->name = $name;
    }

    // .. SNIP ...
}

Test Action:

public function testThingAction($_route)
{
    $em = $this->getDoctrine()->getEntityManager();
    $repo = $em->getRepository('AcmeThingBundle:Thing');

    // simple setup of a couple things in the DB
    $t1 = $repo->findByName('Thing1');
    if (!$t1) {
        $t1 = new Thing('Thing1');
        $t2 = new Thing('Thing2');
        $t2->setParent($t1);

        $em->persist($t1);
        $em->persist($t2);
        $em->flush();
        return $this->redirect($this->generateUrl($_route));
    }

    list($t1, $t2) = $repo->findAll();

    // detach and re-merge Thing1
    // This should cause Thing1 to be removed and then re-added 
    // to the doctrine's known entities; but it doesn't!?
    $em->detach($t1);
    $em->merge($t1);

    // try to update T2
    $t2->setName('Thing2 - ' . time());
    $em->persist($t2);
    // will fail with: 
    // A new entity was found through the relationship Thing#parent
    $em->flush();

    return array();
}

Answer 1

The issue is that the child has a relationship to a specific parent object that is no longer managed by Doctrine. When you call $entityManager->merge($entity) you get a new managed entity back from that function.

When you get that back, you need to manually call setParent() on each of your children with the newly managed entity.