code: def get_relation_count_query(self, query, parent):
          
          parent_table = self._parent.get_table()
  
          self._set_join(query)
  
          query.select(QueryExpression('COUNT(*)'))
  
          key = self.wrap('%s.%s' % (parent_table, self._first_key))
  
          return query.where(self.get_has_compare_key(), '=', QueryExpression(key))
docs: Add the constraints for a relationship count query.
  
          :type query: Builder
          :type parent: Builder
  
          :rtype: Builder