protected function collectForeignKeys()
    {
        $keys = [];

        foreach ($this->info->relations as $relation) {

            if ( ! in_array(
                $relation->type,
                [ RelationType::BELONGS_TO, RelationType::MORPH_TO, RelationType::BELONGS_TO_THROUGH ]
            )) {
                continue;
            }

            $keys = array_merge($keys, $relation->foreign_keys);
        }

        return $keys;
    }