symfony2 Object of class could not be converted to string - arrays

Question

I'm getting some strange error when creating a new user.
Catchable Fatal Error: Object of class Pr\UserBundle\Entity\Group could not be converted to string in /var/www/symfony/webprojekt/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php line 120
This happens, since I changed the choice "usergroup" into a single select for the reason that I don't want to allocate more than one usergroup (e.g. ROLE_USER) to a user.
I added the Entity of User and Group below, but I don't see any problem - I stuck again :(
/**
* #ORM\Entity
* #ORM\Table(name="sys_user")
*/
class User extends BaseUser
{
/**
* #ORM\Column(type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #ORM\Column(type="string", length=8, nullable=true)
*/
protected $mobilepin;
/**
* #ORM\Column(type="integer", nullable=true)
*/
protected $client;
/**
* #ORM\Column(type="integer", nullable=true)
*/
private $client_id;
/**
* #ORM\Column(type="string", length=16383, nullable=true) //16383 = max varchar utf8
*/
private $imageurl;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $firstname;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $lastname;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $emailalert;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
private $phone;
/**
* #ORM\Column(type="integer", nullable = true)
*/
protected $lock_state;
/**
* #ORM\Column(type="array", nullable=true)
* #Assert\NotBlank()(message="Check locations")
*/
private $locations;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
private $usergroups;
/**
* #ORM\Column(type="string", length=5, options={"fixed" = true, "default" = "de_DE"})
*/
private $locale = 'de_DE';
/**
* #ORM\Column(type="string", length=32)
*/
private $timezone = 'UTC';
/**
* #ORM\Column(type="array", nullable=true)
*/
private $created='1';
And the one from my group
/**
* #ORM\Entity
* #ORM\Table(name="user_group")
*/
class Group
{
/**
* #ORM\Column(type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $name;
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $roles;
And at least how I create the choice:
->add('usergroups', 'entity', array('class' => 'PrUserBundle:Group','property' => 'name','required' => true, 'empty_value' => 'Benutzergruppe','multiple' => false, 'expanded' => false))
It is weird :(
EDIT: if I change the "usergroups" from
* #ORM\Column(type="string", length=255, nullable=true)
to
* #ORM\Column(type="array", nullable=true)
it works fine. but then, the save data look like
O:26:"Pr\UserBundle\Entity\Group":3:{s:5:"
which looks very strange and wrong. I thought about saving the ID of the assigned group

Answer 1

If you want to create a relation between User and UserGroups you need to change the column definition from :
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
private $usergroups;
to
/**
* #ManyToMany(targetEntity="Group")
*/
private $usergroups;
and then define the reversed relation in groups:
Group {
/**
* #ManyToMany(targetEntity="User")
*/
private $users;
You can read more about relations in doctrine here: http://docs.doctrine-project.org/en/2.0.x/reference/association-mapping.html or here: http://symfony.com/doc/current/book/doctrine.html#entity-relationships-associations
Piotr

Answer 2

Try to map 'usergroups' field in your User entity to Group entity instead of making it a string field.
/**
* #ManyToOne(targetEntity="Group")
* #JoinColumn(name="group_id", referencedColumnName="id")
*/
private $usergroups;
You may also view documentation about mappings here:
http://symfony.com/doc/current/book/doctrine.html#relationship-mapping-metadata
http://docs.doctrine-project.org/en/2.0.x/reference/association-mapping.html#association-mapping