code: def get_first_category(app_uid):
          '''
          Get the first, as the uniqe category of post.
          '''
          recs = MPost2Catalog.query_by_entity_uid(app_uid).objects()
          if recs.count() > 0:
              return recs.get()
  
          return Nonf get_first_category(app_uid):
          '''
          Get the first, as the uniqe category of post.
          '''
          recs = MPost2Catalog.query_by_entity_uid(app_uid).objects()
          if recs.count() > 0:
              return recs.get()
  
          return None
docs: Get the first, as the uniqe category of post.