Django4.0 迁移-撤销迁移

可以通过 ​migrate ​传递上一次迁移的编号来撤销迁移。例如，要撤销迁移 books.0003：

...\> py manage.py migrate books 0002
Operations to perform:
  Target specific migration: 0002_auto, from books
Running migrations:
  Rendering model states... DONE
  Unapplying books.0003_auto... OK

如果要撤消应用于一个应用的所有迁移，请使用名称 zero：

...\> py manage.py migrate books zero
Operations to perform:
  Unapply all migrations: books
Running migrations:
  Rendering model states... DONE
  Unapplying books.0002_auto... OK
  Unapplying books.0001_initial... OK

如果迁移包含任何不可逆的操作，则该迁移是不可逆的。 试图撤销这种迁移将引发 ​IrreversibleError​：

...\> py manage.py migrate books 0002
Operations to perform:
  Target specific migration: 0002_auto, from books
Running migrations:
  Rendering model states... DONE
  Unapplying books.0003_auto...Traceback (most recent call last):
django.db.migrations.exceptions.IrreversibleError: Operation <RunSQL  sql='DROP TABLE demo_books'> in books.0003_auto is not reversible