Object of class Doctrine\ORM\PersistentCollection could not be converted to string
For manage a ManyToMany relation between User and Mission
in User.php:
/** * @var \Doctrine\Common\Collections\ArrayCollection * * @ORM\ManyToMany(targetEntity="Your\SuperBundle\Entity\Mission", inversedBy="users", orphanRemoval=true) * @ORM\JoinTable(name="user_mission") */private $missions;in Mission.php:
/** * @var \Doctrine\Common\Collections\ArrayCollection * * @ORM\ManyToMany(targetEntity="Your\SuperBundle\Entity\User", mappedBy="missions", cascade={"all"}, orphanRemoval=true) */private $users;then for your form:
http://symfony.com/doc/current/reference/forms/types/collection.html for manage collection of Mission in your User form.
take a look at "type" and "allow_add"