Doctrine2 Entity tree builder O(n)

doctrineTreeBuilder

<?php

/**
 * Cost O(n)
 *
 * This method allow build a tree given following data
 *
 * $entities is an Array ( or any ArrayIterator implementation ) of $entity
 * $entity is an Object ( can be Whatever )
 *
 * In this case:
 *    $entity implements isRoot() what defines if entity is first level
 *    $entity implements getParent(), a doctrine relation with a parent Entity
 */
$tree = array(
    0   =>  null,
    'children'  =>  array(),
);

/*
 * Iterating every entity
 */
foreach (entities as $entity) {

    $parentEntityId = 0;
    entityId = $entity->getId();

    /**
     * If is not root, we need to load parent id without lazy loading it
     * Otherwise, is 0 ( root )
     */
    if (!$entity->isRoot()) {
        $parentEntityId = $this
            ->getDoctrine()
            ->getManager()
            ->getUnitOfWork()
            ->getEntityIdentifier($category->getParent())['id'];
    }
    
    /** 
     * Initizalizing parent block
     */
    if (!isset($tree[$parentEntityId])) {

        $tree[$parentEntityId] = array(
            'entity'    =>  null,
            'children'  =>  array(),
        );
    }

    /**
     * Initializing entity block
     */
    if (!isset($tree[$entityId])) {

        $tree[$entityId] = array(
            'entity'    =>  null,
            'children'  =>  array(),
        );
    }

    /**
     * Setting entity and adding it to parent children
     * Using pointer to fast access to entity for future children
     */
    $tree[$entityId]['entity'] = $entity;
    $tree[$parentEntityId]['children'][] = &$tree[$entityId];
}

/**
 * Full tree is available by getting root children array
 */
$tree = $tree[0]['children'];