添加不可为空的字段（外国）并填充后，如何恢复未完成的 makemigration

Question

我犯了一个错误，添加了一个不可为空的字段并用 1 填充。

contest = models.ForeignKey(Contest, on_delete=models.CASCADE)

（比赛为空，新桌）

 >>> python manage.py makemigrations contests
You are trying to add a non-nullable field 'contest' to contestentry without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now
Type 'exit' to exit this prompt
>>> 1

迁移时出现错误，因为模型的表是空的。

>>> python manage.py migrate contests 
psycopg2.errors.ForeignKeyViolation: insert or update on table "contests_contestentry" violates foreign key constraint "contests_contestentr_contest_id_7f53b874_fk_contests_"
DETAIL:  Key (contest_id)=(1) is not present in table "contests_contest".

我删除了该字段并尝试迁移回来，但它没有工作，然后我尝试恢复迁移，但它给出了以下错误：

>>> python manage.py migrate contests 0007_remove_contestentry_nvotes

    Operations to perform:
      Target specific migration: 0007_remove_contestentry_nvotes, from contests
    Running migrations:
      No migrations to apply.
      Your models have changes that are not yet reflected in a migration, and so won't be applied.
      Run 'manage.py makemigrations' to make new migrations, and then re-run 'manage.py migrate' to apply them.

如何恢复到migration_007，然后在数据库中将该字段设置为空？

Answer 1

您可以通过迁移到以前的迁移来恢复。

例如，如果您的最后两次迁移是：

0010_previous_migration
0011_migration_to_revert

Then you would do:

./manage.py migrate my_app 0010_previous_migration 

然后您可以删除迁移 0011_migration_to_revert。

对于空模型：

contest = models.ForeignKey(Contest, on_delete=models.CASCADE, blank=true)

Answer 2

我通过删除 appname/migrations 中的迁移解决了这个问题，删除了冲突的代码并再次运行 makemigrations migrate