code: def count_of_certain_category(cat_id, tag=''):
          '''
          Get the count of certain category.
          '''
  
          if cat_id.endswith('00'):
              # The first level category, using the code bellow.
              cat_con = TabPost2Tag.par_id == cat_id
          else:
              cat_con = TabPost2Tag.tag_id == cat_id
  
          if tag:
              condition = {
                  'def_tag_arr': [tag]
              }
              recs = TabPost2Tag.select().join(
                  TabPost,
                  on=((TabPost2Tag.post_id == TabPost.uid) & (TabPost.valid == 1))
              ).where(
                  cat_con & TabPost.extinfo.contains(condition)
              )
          else:
              recs = TabPost2Tag.select().where(
                  cat_con
              )
  
          return recs.count(f count_of_certain_category(cat_id, tag=''):
          '''
          Get the count of certain category.
          '''
  
          if cat_id.endswith('00'):
              # The first level category, using the code bellow.
              cat_con = TabPost2Tag.par_id == cat_id
          else:
              cat_con = TabPost2Tag.tag_id == cat_id
  
          if tag:
              condition = {
                  'def_tag_arr': [tag]
              }
              recs = TabPost2Tag.select().join(
                  TabPost,
                  on=((TabPost2Tag.post_id == TabPost.uid) & (TabPost.valid == 1))
              ).where(
                  cat_con & TabPost.extinfo.contains(condition)
              )
          else:
              recs = TabPost2Tag.select().where(
                  cat_con
              )
  
          return recs.count()
docs: Get the count of certain category.