Question

说，我有一个模型Post与User的内置liked_post有很多关系

class Post(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='posts')
    like = models.ManyToManyField(User, related_name='liked_posts')

逻辑上一切都很好，我可以很好地添加/删除喜欢的关系。但是，当我为save引入附加属性saved_post时，就像这样：

class Post(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='posts')
    like = models.ManyToManyField(User, related_name='liked_posts')
    save = models.ManyToManyField(User, related_name='saved_posts')

在尝试实例化Post模型时，它总是在下面抛出错误。

ValueError: "<Post: Post object (None)>" needs to have a value for field "id" before this many-to-many relationship can be used.

请注意，我什至没有修改/添加任何自定义save()方法。

即使我尝试致电p = Post.object.create()，错误也会突然出现。

据我所知，我需要先保存Post，然后再添加任何like或save关系。但是即使保存Post实例，我也出错了。

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编辑1

包括完整的堆栈跟踪：

Error
Traceback (most recent call last):
  File "/home/rahmat/Upworks/06_Made_Gatewee/gatewee/app_post/tests/test_post_save.py", line 34, in setUp
    p = Post.objects.create()
  File "/home/rahmat/Upworks/06_Made_Gatewee/gatewee/venv/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/rahmat/Upworks/06_Made_Gatewee/gatewee/venv/lib/python3.6/site-packages/django/db/models/query.py", line 422, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/rahmat/Upworks/06_Made_Gatewee/gatewee/venv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 527, in __get__
    return self.related_manager_cls(instance)
  File "/home/rahmat/Upworks/06_Made_Gatewee/gatewee/venv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 840, in __init__
    (instance, self.pk_field_names[self.source_field_name]))
ValueError: "<Post: Post object (None)>" needs to have a value for field "id" before this many-to-many relationship can be used.

Answer 1

这里的问题是save模型中的Post字段与内部save方法冲突并导致此错误。

只需更改字段名称，例如：

class Post(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='posts')
    like = models.ManyToManyField(User, related_name='liked_posts')
    saved_posts = models.ManyToManyField(User, related_name='saved_posts')

django-ValueError：<model>必须具有字段“ id”的值，然后才能使用这种多对多关系

1 个答案: