public function addReference(ChildReference $reference)
    {
        if ($this->collReferences === null) {
            $this->initReferences();
        }

        if (!$this->getReferences()->contains($reference)) {
            // only add it if the **same** object is not already associated
            $this->collReferences->push($reference);
            $this->doAddReference($reference);
        }

        return $this;
    }