Entities in the Session

There are several use-cases to save entities in the session, for example:

  1. User object
  2. Multi-step forms

To achieve this with Doctrine you have to pay attention to some details to get this working.

Merging entity into an EntityManager

In Doctrine an entity objects has to be "managed" by an EntityManager to be updateable. Entities saved into the session are not managed in the next request anymore. This means that you have to register these entities with an EntityManager again if you want to change them or use them as part of references between other entities. You can achieve this by calling EntityManager#merge().

For a representative User object the code to get turn an instance from the session into a managed Doctrine object looks like this:

require_once 'bootstrap.php';
$em = GetEntityManager(); // creates an EntityManager 

if (isset($_SESSION['user']) && $_SESSION['user'] instanceof User) {
    $user = $_SESSION['user']; 
    $user = $em->merge($user);

A frequent mistake is not to get the merged user object from the return value of EntityManager#merge(). The entity object passed to merge is not necessarily the same object that is returned from the method.

Serializing entity into the session

Entities that are serialized into the session normally contain references to other entities as well. Think of the user entity has a reference to his articles, groups, photos or many other different entities. If you serialize this object into the session then you don't want to serialize the related entities as well. This is why you should call EntityManager#detach() on this object or implement the __sleep() magic method on your entity.

require_once 'bootstrap.php';
$em = GetEntityManager(); // creates an EntityManager 

$user = $em->find("User", 1);
$_SESSION['user'] = $user;

When you called detach on your objects they get "unmanaged" with that entity manager. This means you cannot use them as part of write operations during EntityManager#flush() anymore in this request.