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_id)
Delete the record of post 2 tag.