code: def remove_relation(post_id, tag_id):
          '''
          Delete the record of post 2 tag.
          '''
          entry = TabPost2Tag.delete().where(
              (TabPost2Tag.post_id == post_id) &
              (TabPost2Tag.tag_id == tag_id)
          )
          entry.execute()
          MCategory.update_count(tag_idf remove_relation(post_id, tag_id):
          '''
          Delete the record of post 2 tag.
          '''
          entry = TabPost2Tag.delete().where(
              (TabPost2Tag.post_id == post_id) &
              (TabPost2Tag.tag_id == tag_id)
          )
          entry.execute()
          MCategory.update_count(tag_id)
docs: Delete the record of post 2 tag.