Knp DoctrineBehaviors Tree getChildNodes - php

Question

I'm learning symfony and currently I'm looking into Knp DoctrineBehaviors Tree, and I'm confused a little bit, because in the trait: https://github.com/KnpLabs/DoctrineBehaviors/blob/master/src/Knp/DoctrineBehaviors/Model/Tree/Node.php there is a $childNodes and getter getChildNodes() which make sense but getChildNodes always returns empty array for me and I agree with this because I don't set $childNodes any where so it will always return empty ArrayCollection. So my question is should my application look after this? Or I undestand that wrongly?
/**
* #var ArrayCollection $childNodes the children in the tree
*/
private $childNodes;
...
...
...
/**
* {#inheritdoc}
**/
public function getChildNodes()
{
return $this->childNodes = $this->childNodes ?: new ArrayCollection;
}
Thanks for any help.

Answer 1

Yes you need to set the child nodes. But the api for doing this are as bellow:
//To set $child as child node for a $parent entity
$child->setParentNode($parent);
//OR
$child->setChildOf($parent);
$parent->isParentOf($child); //return true
$child->isParentOf($parent); //return false
Whenever you need to access getChildNodes() you need Build the tree first:
$root = $em->getRepository('Category')->getTree();
$root->getParent(); // null
$root->getChildNodes(); // ArrayCollection
$root[0][1]; // node or null
$root->isLeaf(); // boolean
$root->isRoot(); // boolean
The idea behind this tree implementation is that there is no relationship between parent and children (foreign key). All the relations are defined via a materialized path, a string stored in each node. So before build tree you can't access this getParentNode() and getChildNodes() functions.
Just for your thought: To get all child by parent_id you can define the following function in your repository
public function getChildrenByParentID($parentId)
{
$parentPath = $this->find($parentId)->getRealMaterializedPath();
return $this->getTree($parentPath)->getChildNodes();
}
Updated: You can use following function(define in your repository class) to read all root level nodes:
public function getRootLevelNodes()
{
$qb = $this->createQueryBuilder('t');
return $qb
->where($qb->expr()->eq('t.materializedPath', '?1'))
->setParameter(1, '');
}
You can read more about Doctrine ORM behaviors, or how to use traits efficiently