How to be warned a many-to-many relation gonna be update? - php

Question

I want to do a specific treatment when a specific field is updated.
The obvious way is to do it with event preUpdate, and see what fields are updated. It works fine ... except for a many-to-many field. It triggers the event, but the ChangeSet is empty.
/**
* #ORM\PreUpdate
*/
public function updateDate(PreUpdateEventArgs $event){
$changeSet = $event->getEntityChangeSet();
$res = "";
foreach($changeSet as $key => $change){
$line = $key." : ".$event->getOldValue($key)." || ".$event->getNewValue($key);
$res .= $line;
}
}
In $res all my fields are modified except for the many-to-many field.
Also, I'm trying to do it in a listener, but I can't find how to extract the fields which are updated from the entityManager.
Thank you.
More informations :
Relation from the update entity :
/**
* #var Status
*
* #ORM\ManyToMany(targetEntity="User", inversedBy="projectsSupervisor", cascade={"persist"})
* #ORM\JoinTable(name="projects_supervisors")
*/
protected $supervisors;
From the other side :
/**
* #var Project
*
* #ORM\ManyToMany(targetEntity="Task", mappedBy="users")
*/
protected *tasks
Symfony version : 3.1.10

Answer 1

It is not possible to track changes made to an many-to-many-association. See here :
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)
Additionally, ::getEntityChangeSet() is only useful for regular fields, not associations. For One-To-Many-Associations, you can use $unitOfWork->getScheduledCollectionUpdates() :
foreach ($uow->getScheduledCollectionUpdates() as $collectionUpdate) {
/** #var $collectionUpdate \Doctrine\ORM\PersistentCollection */
if ($collectionUpdate->getOwner() === $entity) {
// This entity has an association mapping which contains updates.
$collectionMapping = $collectionUpdate->getMapping();
print_r($collectionMapping); // Investigate this further
}
}
A practical example is viewable in my github repository "DoctrineWatcher" which does exactly the same (line 196+).