public function findOneByTerms(Competency $parent, Ability $ability)
    {
        $link = $this->findOneBy(['competency' => $parent, 'ability' => $ability]);

        if (!$link) {
            throw new \RuntimeException(
                "Competency {$parent->getId()} is not linked to ability {$ability->getId()}"
            );
        }

        return $link;
    }