Doctrine2: How to handle missing relation documents - php

Question

within a huge dataset I sometimes get inconsistencies when one document is deleted. Symfony2 App with Doctrine ODM and FosREST
$a = new Element();
$b = new Element();
$c = new List();
$c->addElement($a);
$c->addElement($b);
$em->persist($c);
saving at this point works flawlessly
in 99% of the cases $a and $b are still valid Documents when $c is loaded later.
BUT sometimes either $a or $b is deleted without updating the reference in $c.
-> at this moment the next loading of $c will fail with a \Doctrine\ODM\MongoDB\DocumentNotFoundException
(message is something like: The "MongoDBODMProxies__CG__\App\Model\Element" document with identifier "541417702798711d2900607c" could not be found.)
What is the best approach now to handle this case?
I was thinking about either
catching the Exception and to check if the reference it tried to load was on the Element Model
custom exception Handler in fosRest to check for
custom repository function in the mapping and to check there if everything is still valid (+ to store somehow that there is a missing Element) -> but this then forces me to check on every occasion if the "error" is set
UPDATE: The Mapping between the Documents is a bit more complex than I described here
for one the element is basically a collection separated by a discriminator, where only one type of fields references another document (I call it "Tree" now)
a tree can be used in thousands of ElementTree's (that specific type that contains a Tree)
sometimes Tree's can be deleted (this is already a slow running process since a lot of data needs to be updated then)
I would now need to find out what Lists need to change and basically reject the api calls to those lists with the information that a specific element is no longer available.

Answer 1

A few things to check especially for MongoDB:
Make sure that there are no circular references (for example if you have the property $elements on the class List and references set to true on it, make sure List is not referenced on the Elements class as well) and your mappings are consistent.
In the addElement function IF the reference is held on the Element class make sure you also call $element->setList($this) inside the function. (and the same for removeElement, unset the reference if neccessary)
Make sure you cascade all the necessary operations. (For example cascade : ["persist", "delete", "refresh" or "all" ]
You can check your mappings with
$ app/console doctrine:mongodb:mapping:info
Finally if you expect that document to be deleted but you get an error from the proxy object you can clear the metadata cache
$ app/console doctrine:mongodb:cache:clear-metadata

Answer 2

Inperfect Solution that works for now
I now chose to throw a new Exception (it is important not let doctrine throw one because it will reject then any persist attempts in the same request).
In the PostLoad LifecycleEvent I check now the following (simplified):
if ($document instanceof List) {
foreach ($document->getElements() as $element) {
// at this moment $element->getId() is already defined but not yet loaded from mongo
$result = $this->elementRepository->findBy(array(‘_id’ => $element->getId()));
if (sizeof($result)==0) {
throw new InvalidElementInList($element->getId());
}
}
}
in the RestController this enables me now to catch this specific exception and to remove the invalid element from the list + to return a custom view to the user indicating that the element was removed.