protected function getRelationModel()
    {
        list($model, $attribute) = $this->resolveModelAttribute($this->valueFrom);

        if (!$model) {
            throw new ApplicationException(Lang::get('backend::lang.model.missing_relation', [
                'class' => get_class($this->model),
                'relation' => $this->valueFrom
            ]));
        }

        if (!$model->hasRelation($attribute)) {
            throw new ApplicationException(Lang::get('backend::lang.model.missing_relation', [
                'class' => get_class($model),
                'relation' => $attribute
            ]));
        }

        return $model->makeRelation($attribute);
    }