code: def execute(self, using=None):
          
          if not using:
              using = self.get_connection()
  
          inserted_entities = {}
          for klass in self.orders:
              number = self.quantities[klass]
              if klass not in inserted_entities:
                  inserted_entities[klass] = []
              for i in range(0, number):
                  entity = self.entities[klass].execute(using, inserted_entities)
                  inserted_entities[klass].append(entity)
  
          return inserted_entities
docs: Populate the database using all the Entity classes previously added.
  
          :param using A Django database connection name
          :rtype: A list of the inserted PKs