Doctrine: Object of class User could not be converted to string

Question

I keep getting this error with Doctrine:

PHP Catchable fatal error:  Object of class User could not be converted to string in vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php on line 1337

In my system users can have many permissions in a One to Many relationship. I have set up a User and Permission entity. They look like this (I removed some annotations, getters and setters to reduce clutter):

class User {

   /**
    * @ORM\Column(name="user_id", type="integer", nullable=false)
    * @ORM\Id
    * @ORM\GeneratedValue(strategy="IDENTITY")
    */
   protected $id;

   public function getId()
   {
      return $this->id;
   }

   /**
    * @ORM\OneToMany(targetEntity="Permission", mappedBy="user", cascade={"persist"})
    */
   protected $permissions;

   public function getPermissions()
   {
      return $this->permissions;
   }

}

class Permission {

   /**
    * @ORM\Column(name="user_id", type="integer")
    * @ORM\ManyToOne(targetEntity="User", inversedBy="permissions")
    */
   protected $user;

   public function getUser()
   {
      return $this->user;
   }

   public function setUser( $user )
   {
      $this->user = $user;

      return $this;
   }
}

The problem occurs when I add a new Permission to a User:

$permission = new Permission();

$user->getPermissions()->add( $permission );

$em->persist( $user );
$em->flush();

This is the last bit of my stack trace:

PHP  11. Doctrine\ORM\UnitOfWork->persist() vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php:565
PHP  12. Doctrine\ORM\UnitOfWork->doPersist() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:1555
PHP  13. Doctrine\ORM\UnitOfWork->cascadePersist() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:1615
PHP  14. Doctrine\ORM\UnitOfWork->doPersist() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:2169
PHP  15. Doctrine\ORM\UnitOfWork->persistNew() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:1597
PHP  16. Doctrine\ORM\UnitOfWork->scheduleForInsert() doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:836
PHP  17. Doctrine\ORM\UnitOfWork->addToIdentityMap() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:1157
PHP  18. implode() vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php:1337

Any insight would be greatly appreciated.

Answer 1

OK. I've got it working.

I haven't fully worked out the reason yet but when I add the following to my User entity it works:

class User {    

   public function __toString()
   {
      return strval( $this->getId() );
   }

}

If I find out more I will post here.