Doctrine - self-referencing entity - disable fetching of children

Question

I have a very simple entity(WpmMenu) that holds menu items connected to one another in a self-referencing relationship (adjecent list it's called)? so in my entity I have:

protected $id
protected $parent_id
protected $level
protected $name

with all the getters/setters the relationships are:

/**
* @ORM\OneToMany(targetEntity="WpmMenu", mappedBy="parent")
*/
protected $children;

/**
* @ORM\ManyToOne(targetEntity="WpmMenu", inversedBy="children", fetch="LAZY")
* @ORM\JoinColumn(name="parent_id", referencedColumnName="id", onUpdate="CASCADE", onDelete="CASCADE")
*/
protected $parent;

public function __construct() {
   $this->children = new ArrayCollection();
}

And everything works fine. When I render the menu tree, I get the root element from the repository, get its children, and then loop through each child, get its children and do this recursively until I have rendered each item.

What happens (and for what I am seeking a solution)is this: At the moment I have 5 level=1 items and each of these items have 3 level=2 items attached (and in the future I will be using level=3 items as well). To get all elements of my menu tree Doctrine executes:

• 1 query for the root element +
• 1 query to get the 5 children(level=1) of the root element +
• 5 queries to get the 3 children(level=2) of each of the level 1 items +
• 15 queries (5x3) to get the children(level=3) of each level 2 items

TOTAL: 22 queries

So, I need to find a solution for this and ideally I would like to have 1 query only.

So this is what I am trying to do: In my entities repository(WpmMenuRepository) I use queryBuilder and get a flat array of all menu items ordered by level. Get the root element(WpmMenu) and add "manually" its children from the loaded array of elements. Then do this recursively on children. Doing this way I could have the same tree but with a single query.

So this is what I have:

WpmMenuRepository:

public function setupTree() {
    $qb = $this->createQueryBuilder("res");
    /** @var Array */
    $res = $qb->select("res")->orderBy('res.level', 'DESC')->addOrderBy('res.name','DESC')->getQuery()->getResult();
    /** @var WpmMenu */
    $treeRoot = array_pop($res);
    $treeRoot->setupTreeFromFlatCollection($res);
    return($treeRoot);
}

and in my WpmMenu entity I have:

function setupTreeFromFlatCollection(Array $flattenedDoctrineCollection){
  //ADDING IMMEDIATE CHILDREN
  for ($i=count($flattenedDoctrineCollection)-1 ; $i>=0; $i--) {
     /** @var WpmMenu */
     $docRec = $flattenedDoctrineCollection[$i];
     if (($docRec->getLevel()-1) == $this->getLevel()) {
        if ($docRec->getParentId() == $this->getId()) {
           $docRec->setParent($this);
           $this->addChild($docRec);
           array_splice($flattenedDoctrineCollection, $i, 1);
        }
     }
  }
  //CALLING CHILDREN RECURSIVELY TO ADD REST
  foreach ($this->children as &$child) {
     if ($child->getLevel() > 0) {      
        if (count($flattenedDoctrineCollection) > 0) {
           $flattenedDoctrineCollection = $child->setupTreeFromFlatCollection($flattenedDoctrineCollection);
        } else {
           break;
        }
     }
  }      
  return($flattenedDoctrineCollection);
}

And this is what happens:

Everything works out fine, BUT I end up with each menu items present twice. ;) Instead of 22 queries now I have 23. So I actually worsened the case.

What really happens, I think, is that even if I add the children added "manually", the WpmMenu entity is NOT considered in-sync with the database and as soon as I do the foreach loop on its children the loading is triggered in ORM loading and adding the same children that were added already "manually".

Q: Is there a way to block/disable this behaviour and tell these entities they they ARE in sync with the db so no additional querying is needed?

Answer 1

With immense relief (and a lots of learning about Doctrine Hydration and UnitOfWork) I found the answer to this question. And as with lots of things once you find the answer you realize that you can achieve this with a few lines of code. I am still testing this for unknown side-effects but it seems to be working correctly. I had quite a lot of difficulties to identify what the problem was - once I did it was much easier to search for an answer.

So the problem is this: Since this is a self-referencing entity where the entire tree is loaded as a flat array of elements and then they are "fed manually" to the $children array of each element by the setupTreeFromFlatCollection method - when the getChildren() method is called on any of the entities in the tree (including the root element), Doctrine (NOT knowing about this 'manual' approach) sees the element as "NOT INITIALIZED" and so executes an SQL to fetch all its related children from the database.

So I dissected the ObjectHydrator class (\Doctrine\ORM\Internal\Hydration\ObjectHydrator) and I followed (sort of) the dehydration process and I got to a $reflFieldValue->setInitialized(true); @line:369 which is a method on the \Doctrine\ORM\PersistentCollection class setting the $initialized property on the class true/false. So I tried and IT WORKS!!!

Doing a ->setInitialized(true) on each of the entities returned by the getResult() method of the queryBuilder (using the HYDRATE_OBJECT === ObjectHydrator) and then calling ->getChildren() on the entities now do NOT trigger any further SQLs!!!

Integrating it in the code of WpmMenuRepository, it becomes:

public function setupTree() {
  $qb = $this->createQueryBuilder("res");
  /** @var $res Array */
  $res = $qb->select("res")->orderBy('res.level', 'DESC')->addOrderBy('res.name','DESC')->getQuery()->getResult();
  /** @var $prop ReflectionProperty */
  $prop = $this->getClassMetadata()->reflFields["children"];
  foreach($res as &$entity) {
    $prop->getValue($entity)->setInitialized(true);//getValue will return a \Doctrine\ORM\PersistentCollection
  }
  /** @var $treeRoot WpmMenu */
  $treeRoot = array_pop($res);
  $treeRoot->setupTreeFromFlatCollection($res);
  return($treeRoot);
}

And that's all!