Doctrine 2 - ManyToMany relationship - empty collection - symfony

Question

I have many to many relationship between user and groups, but when I want to access all groups for user I get empty collection.
namespace LoginBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
/**
* #ORM\Entity
* #ORM\Table(name="User")
*/
class User
{
/**
* #ORM\Column(type="integer", name="id")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $_iId;
/**
* #ORM\Column(type="string", name="login", length=45)
*/
private $_sLogin;
/**
* #ORM\ManyToMany(targetEntity="GroupBundle\Entity\Group", inversedBy="_aUser")
* #ORM\JoinTable(name="Group_x_User",
* joinColumns={#ORM\JoinColumn(name="user_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="group_id", referencedColumnName="id")}
* )
*/
private $_aGroup;
public function __construct() {
$this->_aGroup = new ArrayCollection();
}
/**
* Get iId
*
* #return integer
*/
public function getId()
{
return $this->_iId;
}
/**
* Set sLogin
*
* #param string $sLogin
*
* #return User
*/
public function setLogin($sLogin)
{
$this->_sLogin = $sLogin;
return $this;
}
/**
* Get sLogin
*
* #return string
*/
public function getLogin()
{
return $this->_sLogin;
}
public function getGroups()
{
return $this->_aGroup;
}
User and Group use Group_x_User table to store their relationships.
namespace GroupBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
/**
* #ORM\Entity
* #ORM\Table(name="Group")
*/
class Group
{
/**
* #ORM\Column(type="integer", name="id")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $_iId;
/**
* #ORM\Column(type="string", name="name", length=45)
*/
private $_sName;
/**
* #ORM\ManyToMany(targetEntity="LoginBundle\Entity\User", mappedBy="_aGroup")
*/
private $_aUser;
public function __construct() {
$this->_aUser = new ArrayCollection();
}
/**
* Get iId
*
* #return integer
*/
public function getId()
{
return $this->_iId;
}
/**
* Set sName
*
* #param string $sName
*
* #return Group
*/
public function setName($sName)
{
$this->_sName = $sName;
return $this;
}
/**
* Get sName
*
* #return string
*/
public function getName()
{
return $this->_sName;
}
public function getUsers()
{
return $this->_aUser;
}
}
For restoring data from database I use code:
$oUser = $this->getDoctrine()
->getRepository('LoginBundle:User')
->find(2);
$aGroup = $oUser->getGroups();
Unfortunatelly $aGroup collection contains array of 0 elements while in database are records which are matching. What am I missing in my mapping?

Answer 1

There is something missing from your User class. You only declare _aGroup with ArrayCollection. This is not enough. You have to store the data into ArrayCollection.
Add this into User class.
public class addGroups(\GroupBundle\Entity\Group $group)
{
$group->addUsers($this);
$this->_aGroup->add($group);
}
This is for Group class.
public class addUsers(\LoginBundle\Entity\User $user)
{
if (!$this->_aUser->contains($user)) {
$this->_aUser->add($user);
}
}
For more information, you can visit this link.

Answer 2

#ORM\JoinTable() annotation syntax on User::$_aGroup definition is intended to be used for self-referencing relations Doctrine documentation.
Try using simplified syntax :
#JoinTable(name="Group_x_User")
If you use common conventions ('id' as column name for identifiers, and so on) Doctrine and Symfony will do the rest for you.