外键默认值的ValueError [英] ValueError on foreignkey default value

问题描述

我删除了我的 db.sqlite3 和迁移文件夹中的文件，除了 __ init __.py 之外，但包括了 __ pycache __ 文件夹.

I deleted my db.sqlite3 and the file on my migration folder except __init__.py but including the __pycache__ folder.

我的应用程序的模型是一个文件夹中的多个文件，该文件夹中有一个带有某些导入的 __ init __.py 文件和一个 __ all __ 变量(我不知道这有没有关系).

My app's models are multiple files in a folder with an __init__.py file with some import and an __all__ variable (I don't know if this matter).

在提示符下，我给出了第一个迁移命令，它看起来很有效(迁移会话，管理，身份验证，注册，内容类型.没有我的应用程序核心").

From the prompt I give the first migrate command and it look to work (migrating sessions, admin, auth, registration, contenttypes. There isn't my app 'core').

因此，我给出了第一个makemigrations命令，然后再次给出了migration命令.这次它给出了一个错误:

So i give the first makemigrations command and again the migrate command. This time it give an error:

ValueError: invalid literal for int() with base 10: 'basic'

在模型中，有一个ForeignKey字段，其默认值="basic".basic将是相关类的对象，但实际上它不存在(在创建数据库之前，我将填充它).我认为这很正常.

In a model there's an ForeignKey fields with default='basic'. basic will be an object of the related class but actually it don't exist (before I create the database, then I will populate it). I think it's normal.

无论如何，我都更改了default = 1并可以正常工作(但是1不会成为对象，所以这是错误的！)

Anyway I change in default=1 and it works (but 1 will not be an object, so it's wrong!)

我的模型:

Class Payment(models.Model):
    name = models.CharField(max_length=32)

Class ProfileUser(models.Model):
    payment = models.ForeignKey(Payment, blank=True, null=True, 
        default='basic', on_delete=models.PROTECT)
    #etc

有一种使用基本"的方法吗?我宁愿不使用id = 1，因为我不确定基本的ID(请记住现在还不存在).

There is a way to use 'basic'? I prefer to not use id=1 because I'm not sure to know the id that basic will have (remember that now it don't exist yet).

在其他模型中，我有相似的情况，它们似乎起作用了...

Btw in other models I have alike situations and they appear to works...

整个错误:

(myvenv) c:\Python34\Scripts\possedimenti\sitopossedimenti>manage.py migrate
Operations to perform:
  Apply all migrations: contenttypes, core, registration, admin, auth, sessions
Running migrations:
  Rendering model states... DONE
  Applying core.0001_initial...Traceback (most recent call last):
  File "C:\Python34\Scripts\possedimenti\sitopossedimenti\manage.py", line 10, i
n <module>
    execute_from_command_line(sys.argv)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\core\ma
nagement\__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\core\ma
nagement\__init__.py", line 345, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\core\ma
nagement\base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\core\ma
nagement\base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\core\ma
nagement\commands\migrate.py", line 200, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\migr
ations\executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_ini
tial)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\migr
ations\executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_
initial)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\migr
ations\executor.py", line 198, in apply_migration
    state = migration.apply(state, schema_editor)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\migr
ations\migration.py", line 123, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, projec
t_state)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\migr
ations\operations\fields.py", line 62, in database_forwards
    field,
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\back
ends\sqlite3\schema.py", line 221, in add_field
    self._remake_table(model, create_fields=[field])
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\back
ends\sqlite3\schema.py", line 103, in _remake_table
    self.effective_default(field)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\back
ends\base\schema.py", line 210, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\mode
ls\fields\related.py", line 912, in get_db_prep_save
    return self.target_field.get_db_prep_save(value, connection=connection)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\mode
ls\fields\__init__.py", line 728, in get_db_prep_save
    prepared=False)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\mode
ls\fields\__init__.py", line 968, in get_db_prep_value
    value = self.get_prep_value(value)
  File "c:\Python34\Scripts\possedimenti\myvenv\lib\site-packages\django\db\mode
ls\fields\__init__.py", line 976, in get_prep_value
    return int(value)
ValueError: invalid literal for int() with base 10: 'basic'

谢谢

PS:我正在使用python 3.4 Django 1.9 Windows7

PS: I'm using python 3.4 Django 1.9 Windows7

推荐答案

在您的 Payment 模型中，您尚未显式指定主键.因此，django将为您创建一个.这将是一个整数自动递增字段.

In your Payment model you have not explicitly designated a primary key. So django will create one for you. It will be an integer auto increment field.

Class Payment(models.Model):
    name = models.CharField(max_length=32)

现在，当您将 Payment 定义为 ProfileUser 的外键时，django认为应该将其作为 Payment 中的主键字段用作参考.

Now when you define Payment as a foreign key for ProfileUser, django thinks that it should be the primary key field in Payment that ought to be used as the reference.

Class ProfileUser(models.Model):
    payment = models.ForeignKey(Payment, blank=True, null=True, 
        default='basic', on_delete=models.PROTECT)
    #etc

为了强制执行此引用，付款字段必须为整数.而且您不能在整数字段中插入基本".

In order to enforce this reference, the payment field needs to be an integer. And you cannot insert 'basic' into an integer field.

一种解决方案是使用 ForeignKey.to_field 选项明确引用Payment类中的其他字段.

One solution is to use the ForeignKey.to_field option to explicitly refer to a different field in the Payment class.

ForeignKey.to_field¶与相关对象有关的字段是.默认情况下，Django使用相关对象的主键.

ForeignKey.to_field¶ The field on the related object that the relation is to. By default, Django uses the primary key of the related object.

这样您的班级就会变成

Class ProfileUser(models.Model):
    payment = models.ForeignKey(Payment, blank=True, null=True, 
        default='basic', on_delete=models.PROTECT,
        to_field = 'name' )
    #etc

现在，此处的付款字段变为CharField.请注意，在大多数情况下，使用整数字段作为外键会更有效.

Now the payment field here becomes a CharField. Note that it would be more efficient to use an integer field as a foreign key in most cases.

另一种可能性是，您可以定义 Payment 中的 name 字段作为主键.

Another possibility is for you to define the name field in Payment as it's primary key.

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