在添加不可为空的字段外国并填充字段后，如何恢复未完成的makemigration

如何解决在添加不可为空的字段外国并填充字段后，如何恢复未完成的makemigration

我犯了一个错误，即添加一个非nullablle字段并将其填充为1。

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

（比赛为空，新建表格）

 >>> 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

由于模型表为空，因此迁移时出现错误。

>>> 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向后迁移，但没有成功，然后我尝试还原迁移，但出现以下错误：

>>> 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.

如何恢复为migration_007，然后将该字段设置为能够在数据库中为空？

解决方法

您可以通过迁移到上一个迁移来还原。

例如，如果您最近的两次迁移是：

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)

,

我通过删除应用名称/迁移中的迁移来解决此问题，删除了有冲突的代码，然后再次运行makemigrations迁移