Initializing empty relationships in entities - doctrine-orm

Question

I have entities with 1:1 or 1:M relations to other entities. All relations however are nullable.
I want to proxy some operations to the related entity. I'm giving example below. The problem is that if the relation still does not exist, I have null, so I'm ending up constantly checking for nulls, which obviously is wrong. What I would like to do is to hydrate my entities with empty objects. Reasons:
Doctrine knows what instance should be created for the field anyway. So it should just provide empty instance instead of null
I don't want to fill my code with initializations, like
$object->setSettings(new SettingsEntity)
If the requests should be proxied is somehow disputable, but I want to hide the DB representation from the client code. If my direction however is totally wrong, please point me to the right direction. I may accept that this is responsibility of the model, not of the entity, but Doctrine always returns entities to me
Sure, I can add the initialization either in the constructor of the entity, or to provide getter that creates a new instance of the object, if such does not exists. There are couple of reasons I don't want this:
I don't know how objects are actually hydrated. I assume such initialization should happen in an event and not in the constructor
I don't want to write the code for each entity (at some point, someone will forget to add the initialization in the getter) and want to make it automatically for each relation instead.
Some example code:
/**
* SomeObject
* #ORM\Entity()
* #ORM\Table(
name="some_object"
* )
*/ class SomeObject implements DataTransfer {
/**
* #ORM\OneToOne(targetEntity="Settings", mappedBy="SomeObject")
*/
protected $settings;
public function getSettings() {
return $this->settings;
}
public function get() {
$record = new \stdClass();
$record->id = $this->getId();
...
$settingsObject = $this->getSettings();
$record->someKey = $settingsObject ? $settingsObject->getSomeKey() : null;
$record->someOtherKey = $settingsObject ? $settingsObject->getSomeOtherKey() : null;
return $record;
}
Any suggestions, including hacking Doctrine, are welcome.
P.S. Doctrine-ORM version is 2.3. I can upgrade if this will help solving the problem.

Answer 1

I won't discuss your proxy-thingie-theory: your code, your design, I don't have enough knowlegde of these to have an opinion.
About you knowing how Doctrine hydrates its entities, you can see how it's done in \Doctrine\ORM\UnitOfWork::createEntity. It doesn't seem to invoke the constructor (uses \ReflectionClass::newInstanceWithoutConstructor, which obviously shouldn't use the constructor), but you may be interested in listening to Doctrine's post-load event (part of the lifecycle events logic).
About initializing your null properties, i.e. the code that your post-load event should trigger, you should begin by having a superclass over all of your entities: instead of class SomeObject implements DataTransfer {...}, you'd have class SomeObject extends MyEntity {...} (and have MyEntity implement DataTransfer to keep your interface). This MyEntity class would be a "mapped superclass", it would be annotated with #HasLifecycleCallbacks, and declare a method annotated with #PostLoad. There you have your hook to run your null-to-something code.
For this code to be generic (as it'd be coded from this superclass), you can rely on Doctrine's entity metadata, which retains association mappings and all data that the Unit Of Work needs to figure out its low-level DB-accessing business. It should look like the following:
/** #HasLifecycleCallbacks #MappedSuperclass ... */
public class MyEntity implements DataTransfer {
...
/** #PostLoad */
public function doPostLoad(\Doctrine\Common\Persistence\Event\LifecycleEventArgs $event) { //the argument is needed here, and is passed only since 2.4! If you don't want to upgrade, you can work around by using event listeners, but it's more complicated to implement ;)
$em = $event->getEntityManager();
$this->enableFakeMappings($em);
}
private function enableFakeMappings(\Doctrine\ORM\EntityManager $em) {
$mappings = $em->getClassMetadata(get_class($this))->getAssociationMappings(); //try and dump this $mappings array, it's full o'good things!
foreach ($mappings as $mapping) {
if (null === $this->{$mapping['fieldName']}) {
$class = $mapping['targetEntity'];
$this->{$mapping['fieldName']} = new $class(); //this could be cached in a static and cloned when needed
}
}
}
}
Now, consider the case where you have to new an entity, and want to access its properties without the null values checks: you have to forge a decent constructor for this job. As you still need the Entity Manager, the most straightforward way is to pass the EM to the constructor. In ZF2 (and Symfony I believe) you can have a service locator injected and retrieve the EM from there. Several ways, but it's another story. So, the basic, in MyEntity:
public function __construct(\Doctrine\ORM\EntityManager $em) {
$this->enableFakeMappings($em);
}
Doing this, however, would probably confuse Doctrine when the entity is persisted: what should it do with all these instantiated empty objects? It'll cascade-persist them, which is not what you want (if it is, well, you can stop reading ;)). Sacrificing cascade-persisting, an easy solution would be something like this, still in your superclass:
/** #PrePersist */
public function doPrePersist(\Doctrine\Common\Persistence\Event\LifecycleEventArgs $event) {
$em = $event->getEntityManager();
$this->disableFakeMappings($em);
}
/** #PreUpdate */
public function doPreUpdate(\Doctrine\Common\Persistence\Event\LifecycleEventArgs $event) {
$em = $event->getEntityManager();
$this->disableFakeMappings($em);
}
private function disableFakeMappings(\Doctrine\ORM\EntityManager $em) {
$uow = $em->getUnitOfWork();
$mappings = $em->getClassMetadata()->getAssociationMappings();
foreach ($mappings as $mapping) {
if (!$this->{$mapping['fieldName']} instanceof MyEntity) {
continue;
}
//"reset" faked associations: assume they're fake if the object is not yet handled by Doctrine, which breaks the cascading auto-persist... risk nothing, gain nothing, heh? ;)
if (null === $uow->getEntityState($this->{$mapping['fieldName']}, null)) {
$this->{$mapping['fieldName']} = null;
}
}
}
Hope this helps! :)