Python 错误：“您正在尝试添加不可为空的字段”

Error : "You are trying to add a non-nullable field"

提问by Naresh

I defined below model and getting

我定义了下面的模型并得到

error : You are trying to add a non-nullable field 'user' to videodata without a default; we can't do that

错误 ： You are trying to add a non-nullable field 'user' to videodata without a default; we can't do that

models.py

模型.py

class User(Model):
    userID = models.IntegerField()
    userName = models.CharField(max_length=40)
    email = models.EmailField()
    class Meta:
        ordering = ['userName']
        verbose_name = 'User MetaData'
        verbose_name_plural = 'Users MetaData'
    def __unicode__(self):
        return str(self.userName)

class VideoData(Model):
    video = models.CharField(max_length=40)
    time  = models.IntegerField()
    user = models.ForeignKey(User, related_name='User')
    class Meta:
        verbose_name = 'User_Video MetaData'

Where i am doing wrong????

我哪里做错了？？？？

采纳答案by wobbily_col

As the error says, your user field on VideoData is not allowing nulls, so you either need to give it a default user or allow nulls. Easiest way is to allow nulls.

正如错误所说，您在 VideoData 上的用户字段不允许空值，因此您需要为其提供默认用户或允许空值。最简单的方法是允许空值。

user = models.ForeignKey(User, related_name='User', null=True)

or have a default user

或者有一个默认用户

user = models.ForeignKey(User, related_name='User', default=<have your default user id here>)

回答by btaek

I have run into the same problem with my OneToOneField. And, what I did was to delete all the migration files (which are under the directory of migrationsunder your app), and ran:

我的 OneToOneField 遇到了同样的问题。而且，我所做的是删除所有迁移文件（migrations在您的应用程序下的目录下），然后运行：

python manage.py makemigrations

and

和

python manage.py migrate

I don't know why, but it worked in my case. It won't hurt you to try what I wrote above.

我不知道为什么，但它在我的情况下有效。尝试我上面写的不会伤害你。

Good luck!

祝你好运！

回答by allsyed

Here is what I did to fix the same issue

这是我为解决相同问题所做的工作

1. Comment the foreign key reference in videodataand run the makemigrations and migrate
2. Add the model in admins.pyand make a new entry in table
3. Now uncomment the foreign key reference and provide a default=1.Run make migrations and migrate
4. Remove the default=1in foreign key field.

1. 注释videodata 中的外键引用并运行 makemigrations 和 migrate
2. 在admins.py 中添加模型并在表中创建一个新条目
3. 现在取消注释外键引用并提供default=1.Run make migrations and migrate
4. 删除外键字段中的default=1。

Hope this helps. This solution will work everytime you face these kinds of error.

希望这可以帮助。每当您遇到此类错误时，此解决方案都会起作用。

回答by Guihai

Here is what I do:

这是我所做的：

1. change requirement = models.ForeignKey(Requirement)to requirement = models.ForeignKey(Requirement, null=True)
2. run makemigrations and migrate
3. change back requirement = models.ForeignKey(Requirement, null=True)to requirement = models.ForeignKey(Requirement)
4. run makemigrations and migrate again.

1. 更改requirement = models.ForeignKey(Requirement)为requirement = models.ForeignKey(Requirement, null=True)
2. 运行 makemigrations 并迁移
3. 变回requirement = models.ForeignKey(Requirement, null=True)至 requirement = models.ForeignKey(Requirement)
4. 运行 makemigrations 并再次迁移。

I guess the rule of django-orm about foreignKey is:

我猜 django-orm 关于 foreignKey 的规则是：

1. allow foreignKey to be null when first create table
2. reject to add a foreignKey which is null, because the foreignKey of the data insert into table before will be null, which against programmer's will
3. allow to change foreignKey from not null to null.

1. 首次创建表时允许外键为空
2. 拒绝添加一个为空的外键，因为之前插入表的数据的外键将为空，这违背了程序员的意愿
3. 允许将外键从非空更改为空。

回答by Kurian Benoy

Most of these kind of situtions are not a problem of not adding files to model (using makemigrations and migrate)

大多数此类情况都不是不向模型添加文件的问题（使用 makemigrations 和 migrate）

But due to improper errors in type of Fields models and forms(HERE it was due to inproper syntax error of Foreign Key)

但是由于 Fields 模型和表单的类型错误（这里是由于外键的语法错误不正确）

So first refer:https://www.djangoproject.com/

所以先参考：https: //www.djangoproject.com/

There can be other reasons as Well :

可能还有其他原因：

Sometimes database get populated and it will only accept Non Nullable Value (This error is quite frequent in new versions of django

有时数据库被填充，它只会接受非空值（这个错误在新版本的 django 中很常见

SO also set condition (null==True) in Your model

所以还在你的模型中设置条件 (null==True)

回答by christianbueno.1

The problem sometimes happens when you make a lot of changes in your models.py file (in my case It was related to an ImageField non-nullable field). Rather than field problems indeed. One solution in django 2.0.2 , python 3.6.4 , mysql 5.7.21

当您对 models.py 文件进行大量更改时，有时会出现问题（在我的情况下，它与 ImageField 不可为空字段有关）。而不是领域问题。django 2.0.2、python 3.6.4、mysql 5.7.21中的一种解决方案

• Delete all files inside migrations folder general_app/migrations/*.py, except __init__.py, be careful.

• 删除 migrations 文件夹中的所有文件general_app/migrations/*.py，除了__init__.py，要小心。

You could check if the problem was fixed, if not:

您可以检查问题是否已解决，如果没有：

• Repeat the above step, and
• Delete your database (e.g. in mysql mysql> DROP DATABASE <name_db>)
• Now create a new one with the same name mysql> CREATE DATABASE <name_db>.

• 重复以上步骤，然后
• 删除您的数据库（例如在 mysql 中mysql> DROP DATABASE <name_db>）
• 现在新建一个同名的mysql> CREATE DATABASE <name_db>。

These steps fixed the issue in my case. Now you could run without mistakes:

这些步骤解决了我的问题。现在你可以毫无错误地运行：

$ python manage.py makemigrations
$ python manage.py migrate

回答by joe-khoa

I have faced the same issue: ...non-nullable field 'user' to videodata...

我遇到了同样的问题：...非空字段“用户”到视频数据...

model: Videodata

型号：Videodata

field: user

领域：用户

just add one more attr in the field user of the model Videodata: default=''

只需在模型 Videodata 的字段 user 中再添加一个 attr：default=''