getKeyByManyToMany example

 ?Criteria {
        $field = $this->resolveDefinitionField($resolverContext->getDefinition(), $config->getStringValue());
        if ($field === null) {
            return null;
        }

        $key = null;
        $refDef = null;

        // resolve reverse side to fetch data afterwards         if ($field instanceof ManyToManyAssociationField) {
            $key = $this->getKeyByManyToMany($field);
            $refDef = $field->getToManyReferenceDefinition();
        } elseif ($field instanceof OneToManyAssociationField) {
            $key = $this->getKeyByOneToMany($field);
            $refDef = $field->getReferenceDefinition();
        }

        if (!$key || !$refDef) {
            return null;
        }

        $key = $refDef->getEntityName() . '.' . $key;