问题描述

如 扩展现有用户模型.配置文件模型与另一个模型具有可选的多对一关系:

I created a 'profile' model (with a 1-to-1 relationship to the User model) as described on Extending the existing user model. The profile model has an optional many-to-one relationship to another model:

class Profile(models.Model):
    user = models.OneToOneField(User, primary_key=True)
    account = models.ForeignKey(Account, blank=True, null=True, on_delete=models.SET_NULL)

正如那里记录的那样，我还创建了一个内联管理员:

As documented there, I also created an inline admin:

class ProfileInline(admin.StackedInline):
    model = Profile
    can_delete = False
    verbose_name_plural = 'profiles'
# UserAdmin and unregister()/register() calls omitted, they are straight copies from the Django docs

现在，如果我在创建用户时没有在管理员中选择 account，则不会创建配置文件模型.所以我 连接到 post_save 信号，再次遵循文档:

Now if I don't select an account in the admin when creating the user, the profile model won't be created. So I connect to the post_save signal, again just following the documentation:

@receiver(post_save, sender=User)
def create_profile_for_new_user(sender, created, instance, **kwargs):
    if created:
        profile = Profile(user=instance)
        profile.save()

只要我在管理员中不选择一个 account 就可以正常工作，但如果我这样做了，我会得到一个 IntegrityError 异常，告诉我 duplicate key value 违反了唯一约束app_profile_user_id_key" DETAIL: Key (user_id)=(15) already exists.

This works fine as long as I do not select an account in the admin, but if I do, I'll get an IntegrityError exception, telling me that duplicate key value violates unique constraint "app_profile_user_id_key" DETAIL: Key (user_id)=(15) already exists.

显然，内联管理员尝试自己创建 profile 实例，但我的 post_save 信号处理程序当时已经创建了它.

Apparently, the inline admin tries to creates the profile instance itself, but my post_save signal handler has already created it at that time.

如何解决这个问题，同时满足以下所有要求?

How do I fix this problem, while keeping all of the following requirements?

1. 无论新用户如何创建，之后总会有一个 profile 模型链接到它.
2. 如果用户在创建用户的过程中在管理员中选择了一个account，那么这个account 将会在之后被设置在新的profile 模型上.如果不是，则该字段为 null.

1. No matter how the new user is created, there will always be a profile model linking to it as well afterwards.
2. If the user selects an account in the admin during user creation, this account will be set on the new profile model afterwards. If not, the field is null.

环境:Django 1.5、Python 2.7

Environment: Django 1.5, Python 2.7

相关问题:

• 创建扩展的用户配置文件(类似的症状，但原因竟然是与众不同)

• Creating a extended user profile (similar symptoms, but the cause turned out to be a different one)

推荐答案

可以通过在 OneToOneField 上设置 primary_key=True 指向 用户 模型，正如你自己想出来的那样.

The problem can be avoided by setting primary_key=True on the OneToOneField pointing at the User model, as you have figured out yourself.

这行得通的原因似乎很简单.

The reason that this works seems to be rather simple.

当您尝试创建模型实例并在保存之前手动设置 pk 时，Django 将尝试使用该 pk 在数据库中查找记录并更新它而不是盲目地尝试创建一个新的.如果不存在，它会按预期创建新记录.

When you try to create a model instance and set the pk manually before saving it, Django will try to find a record in the database with that pk and update it rather than blindly attempting to create a new one. If none exists, it creates the new record as expected.

当您将 OneToOneField 设置为主键并且 Django 管理员将该字段设置为相关 User 模型的 ID 时，这意味着 pk已设置，Django 将首先尝试查找现有记录.

When you set the OneToOneField as the primary key and Django Admin sets that field to the related User model's ID, that means the pk is already set and Django will attempt to find an existing record first.

这是将 OneToOneField 设置为主键时发生的情况:

This is what happens with the OneToOneField set as primary key:

1. Django Admin 创建新的 User 实例，没有 id.
2. Django Admin 保存 User 实例.

1. Django Admin creates the new User instance, with no id.
2. Django Admin saves the User instance.

1. 因为 pk(本例中为 id)未设置，Django 尝试创建新记录.
2. 新记录的id由数据库自动设置.
3. post_save 挂钩为该 User 实例创建一个新的 Profile 实例.

1. Because the pk (in this case id) is not set, Django attempts to create a new record.
2. The new record's id is set automatically by the database.
3. The post_save hook creates a new Profile instance for that User instance.

如果你没有显式设置主键，Django 会添加一个使用数据库的 auto_increment 功能的字段:数据库将 pk 设置为下一个最大值那不存在.这意味着该字段实际上将留空，除非您手动设置它，因此 Django 将始终尝试插入新记录，从而导致与 OneToOneField 上的唯一性约束冲突.

If you don't set the primary key explicitly, Django instead adds a field that uses the database's auto_increment functionality: the database sets the pk to the next largest value that doesn't exist. This means the field will actually be left blank unless you set it manually and Django will therefore always attempt to insert a new record, resulting in a conflict with the uniqueness-constraint on the OneToOneField.

这是导致原始问题的原因:

This is what causes the original problem:

1. Django Admin 创建新的 User 实例，没有 id.
2. Django Admin 保存 User 实例，post_save 钩子像以前一样创建一个新的 Profile 实例.
3. Django Admin 创建新的 Profile 实例，没有 id(自动添加的 pk 字段).
4. Django Admin 保存 Profile 实例.

1. Django Admin creates the new User instance, with no id.
2. Django Admin saves the User instance, the post_save hook creating a new Profile instance as before.
3. Django Admin creates the new Profile instance, with no id (the automatically added pk field).
4. Django Admin saves the Profile instance.

1. 因为 pk(本例中为 id)未设置，Django 尝试创建新记录.
2. 数据库报告在 user 字段中违反了表的唯一性约束.
3. Django 抛出异常.你今天不会去太空.

1. Because the pk (in this case id) is not set, Django attempts to create a new record.
2. The database reports a violation of the table's uniqueness-constraint on the user field.
3. Django throws an Exception. You will not go to space today.

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