Doctrine2 many to many - save both sides

Question

I am using Symfony (2.7.5) and Doctrine to manage my data.
I have set up a many to many relationship between users and groups and want to be able to updated this from both the user and group form.
I can only get it to save from the owning side.

User Entity:

/**
* @ORM\ManyToMany(targetEntity="Group", inversedBy="users")
* @ORM\JoinTable(name="users_groups")
**/
private $groups;

/**
* Add group
*
* @param \AppBundle\Entity\Group $group
*
* @return User
*/
public function addGroup(\AppBundle\Entity\Group $group)
{
    if ($this->groups->contains($group)) {
        return;
    }
    $this->groups->add($group);
    $group->addUser($this);
}

/**
* Remove group
*
* @param \AppBundle\Entity\Group $group
*/
public function removeGroup(\AppBundle\Entity\Group $group)
{
    if (!$this->groups->contains($group)) {
        return;
    }
    $this->groups->removeElement($group);
    $group->removeUser($this);
}

/**
* Get groups
*
* @return \Doctrine\Common\Collections\Collection
*/
public function getGroups()
{
    return $this->groups;
}

User form;

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('groups', 'entity', [
                'class' => 'AppBundle:Group',
                'choice_label' => 'name',
                'expanded' => true,
                'multiple' => true,
        ]);
}

Group Entity;

/**
  * @ORM\ManyToMany(targetEntity="User", mappedBy="groups")
  **/
private $users;

/**
* Add user
*
* @param \AppBundle\Entity\User $user
*
* @return Group
*/
public function addUser(\AppBundle\Entity\User $user)
{
    if ($this->users->contains($user)) {
        return;
    }
    $this->users->add($user);
    $user->addGroup($this);
}

/**
* Remove user
*
* @param \AppBundle\Entity\User $user
*/
public function removeUser(\AppBundle\Entity\User $user)
{
    if (!$this->users->contains($user)) {
        return;
    }
    $this->users->removeElement($user);
    $user->removeGroup($this);
}

/**
* Get users
*
* @return \Doctrine\Common\Collections\Collection
*/
public function getUsers()
{
    return $this->users;
}

Group form;

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('groups', 'entity', [
                'class' => 'AppBundle:User',
                'choice_label' => 'name',
                'expanded' => true,
                'multiple' => true,
        ]);
}

Answer 1

Changes made only to the inverse side of an association are ignored. Make sure to update both sides of a bidirectional association (or at least the owning side, from Doctrine's point of view)

Source: http://doctrine-orm.readthedocs.org/projects/doctrine-orm/en/latest/reference/unitofwork-associations.html

Answer 2

For me to get my ManyToMany relationship working right I ended up just specifying everything in the mapping. So you might have something like...

 // src/AppBundle/Entity/Users.php
 /**
 * @Var group
 * @ORM\ManyToMany(targetEntity="Group", fetch="EAGER", cascade={"persist"}, inversedBy="users")
 * @ORM\JoinTable(name="users_groups",
 *      joinColumns={@ORM\JoinColumn(name="group_id", referencedColumnName="group_id")},
 *      inverseJoinColumns={@ORM\JoinColumn(name="user_id", referencedColumnName="user_id")}
 * )
 */

and

    // src/AppBundle/Entity/Group.php
         /**
 * @Var Users
 * @ORM\ManyToMany(targetEntity="Users", fetch="EAGER", cascade={"persist"}, inversedBy="group")
 * @ORM\JoinTable(name="users_groups",
 *      joinColumns={@ORM\JoinColumn(name="user_id", referencedColumnName="user_id")},
 *      inverseJoinColumns={@ORM\JoinColumn(name="group_id", referencedColumnName="group_id")}
 * )
 */