當添加保存的FK時，無法調用NoneType對象

Question

我收到錯誤消息當試圖保存Campaign時，'NoneType'對象不可調用。在Django中是否意味着一旦我保存了對象SingleVoucherReward()我無法訪問它並且無法將其分配給我的Campaign對象？

single_voucher_reward = SingleVoucherReward() 
single_voucher_reward.description = "test" 
single_voucher_reward.save() 

Campaign.participant_reward(single_voucher_reward) 
Campaign.save() 

型號：

class Campaign(models.Model): 
    name = models.CharField(max_length=60, help_text="Give your campaign a name i.e Xmas Offer") 

    participant_reward_content_type = models.ForeignKey(ContentType, 
                 editable=False, 
                 related_name='%(app_label)s_%(class)s_as_participant', 
                 ) 
    participant_reward_object_id = models.PositiveIntegerField() 
    participant_reward = generic.GenericForeignKey('participant_reward_content_type', 'participant_reward_object_id') 

Answer 1

你把東西分配給類，這個類的不是實例。嘗試：

campaign = Campaign() 
campaign.participant_reward = single_voucher_reward 
campaign.save() 

或

campaign = Campaign(participant_reward = single_voucher_reward) 
campaign.save()