docs: def _replace_placeholder(self, spider):
          """
          Returns replaced db_name and collection_name(base on spider's name).
          if your db_name or collection_name does not have a placeholder or
          your db_name or collection_name that not base on spider's name
          you must override this function.
          """
          return self.db_name % {'spider': spider.name}, self.collection_name % {'spider': spider.name}