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首页 > 解决方案 > django - 值错误：在可以使用这种多对多关系之前，需要为字段“id”设置一个值

django - django - 值错误：在可以使用这种多对多关系之前，需要为字段“id”设置一个值

问题描述

说，我有一个模型与内置的Post多对多关系Userliked_post

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/删除类似的关系。但是当我为 引入附加属性save时saved_post，如下所示：

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')

当我尝试实例化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。

即使我尝试调用该错误也会弹出p = Post.object.create()。

据我所知，Post在添加任何like或save关系之前，我需要先保存。但即使保存 Post 实例，我也遇到了错误。

====

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.

标签： djangodjango-models

解决方案

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

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')

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