Flatten transformation for Neos CMS Content Repository

FlattenTransformation.php

<?php
declare(strict_types=1);

namespace My\Site\ContentRepository\Transformations;

use Neos\ContentRepository\Domain\Model\NodeInterface;
use Neos\ContentRepository\Domain\Model\NodeData;
use Neos\ContentRepository\Migration\Transformations\AbstractTransformation;
use Neos\Neos\Controller\CreateContentContextTrait;

/**
 * Move content of a content collection to its parent
 */
class FlattenTransformation extends AbstractTransformation
{
    use CreateContentContextTrait;

    public function isTransformable(NodeData $node): bool
    {
        $numberOfChildNodes = $node->getNumberOfChildNodes('Neos.Neos:ContentCollection', $node->getWorkspace(), $node->getDimensions());
        return ($numberOfChildNodes > 0);
    }

    public function execute(NodeData $node): void
    {
        $contentContext = $this->createContextMatchingNodeData($node);
        $parentNode = $contentContext->getNodeByIdentifier($node->getIdentifier());

        if (!$parentNode) {
            return;
        }

        $contentCollections = $parentNode->getChildNodes('Neos.Neos:ContentCollection');

        foreach ($contentCollections as $contentCollection) {
            if ($contentCollection->hasChildNodes()) {
                $this->moveChildNodesToParent($contentCollection->getChildNodes(), $parentNode);
            }
            $contentCollection->remove();
        }
    }

    /**
     * @param NodeInterface[] $children
     * @param NodeInterface $parentNode
     */
    protected function moveChildNodesToParent(array $children, NodeInterface $parentNode): void
    {
        foreach ($children as $childNode) {
            $childNode->moveInto($parentNode);
        }
    }
}