public function getRelationship($modelName, $navigationName)
    {
        $modelName = $this->getModelClass($modelName);

        if (!isset($this->relationships[$modelName])) {
            return null;
        }

        if (!isset($this->relationships[$modelName][$navigationName])) {
            return null;
        }

        return $this->relationships[$modelName][$navigationName];
    }