Django South 迁移错误：密钥不存在

Question

我将这些字段添加到我的模型中：

class WatchList(models.Model):
    name = models.CharField(max_length=20)

class Thing(models.Model):
    watchlist = models.ForeignKey(WatchList)

成功运行架构迁移：

 >>> $ python2.7 manage.py schemamigration myapp --auto
 + Added model myapp.WatchList
 ? The field 'Thing.watchlist' does not have a default specified, yet is NOT NULL.
 ? Since you are adding this field, you MUST specify a default
 ? value to use for existing rows. Would you like to:
 ?  1. Quit now, and add a default to the field in models.py
 ?  2. Specify a one-off value to use for existing columns now
 ? Please select a choice: 2
 ? Please enter Python code for your one-off default value.
 ? The datetime module is available, so you can do e.g. datetime.date.today()
 >>> 0
 + Added field watchlist on myapp.Thing
 Created 0004_auto__add_watchlist__add_field_thing_watchlist.py. You can now apply this migration with: ./manage.py migrate myapp

在尝试执行此操作之前我没有遇到任何问题，但由于某种原因我收到以下错误：

 >>> $ python2.7 manage.py migrate myapp
FATAL ERROR - The following SQL query failed: ALTER TABLE "myapp_thing" ADD CONSTRAINT "watchlist_id_refs_id_1b2eef756112b8e" FOREIGN KEY ("watchlist_id") REFERENCES "myapp_watchlist" ("id") DEFERRABLE INITIALLY DEFERRED;
The error was: insert or update on table "myapp_thing" violates foreign key constraint "watchlist_id_refs_id_1b2eef756112b8e"
DETAIL:  Key (watchlist_id)=(0) is not present in table "myapp_watchlist".

如何成功地将更改迁移到模型？感谢您提供任何可能有帮助的想法！

Answer 1

这是因为您在迁移中将0 指定为默认值。删除迁移并再次运行，这次指定一个空字符串作为默认值。

如果数据库中已有一些数据，则需要在 ForeignKey 中指定 null=True 和 blank=True，否则会中断。