Neos CMS FlowQuery operation to filter a collection of Nodes having a reference to a given Node

ContainsReferenceToNodeOperation.php

<?php
namespace Visol\FoobarCom\FlowQuery\Operation;

use Neos\ContentRepository\Domain\Model\NodeInterface;
use Neos\Eel\FlowQuery\FlowQuery;
use Neos\Eel\FlowQuery\Operations\AbstractOperation;

class ContainsReferenceToNodeOperation extends AbstractOperation
{

    /**
     * {@inheritdoc}
     *
     * @var string
     */
    static protected $shortName = 'containsReferenceToNode';

    /**
     * {@inheritdoc}
     *
     * @param FlowQuery $flowQuery the FlowQuery object
     * @param array $arguments the arguments for this operation
     * @return void
     */
    public function evaluate(FlowQuery $flowQuery, array $arguments)
    {
        /** @var string $propertyName */
        $propertyName = $arguments[0];
        /** @var NodeInterface $node */
        $nodeToCheckForReference = $arguments[1];

        $context = $flowQuery->getContext();

        foreach ($context as $key => $node) {
            /** @var $node NodeInterface */
            $references = $node->getProperty($propertyName);

            $deleteFromContext = true;

            if (is_array($references)) {
                foreach ($references as $referencedNode) {
                    /** @var $referencedNode NodeInterface */
                    if ($referencedNode === $nodeToCheckForReference) {
                        // The node is references, so it stays in the context
                        $deleteFromContext = false;
                        break;
                    }
                }
            }

            // Node is not referenced
            if ($deleteFromContext) {
                unset($context[$key]);
            }
        }

        $flowQuery->setContext(array_values($context));
    }
}

teachersTeachingOffer.fusion

teachers = Neos.Fusion:Collection {
    collection = ${q(site).find('[instanceof Visol.FoobarCom:Document.Teacher]').containsReferenceToNode('offers', node).get()}
    itemName = 'teacher'
    itemRenderer = Visol.FoobarCom:Component.Molecule.TeacherTeaser {
        teacher = ${teacher}
    }
}