我在 Django 中更改 ManyToMany 字段时是否破坏了我的数据库？

Question

所以我有一个 ForeignKey 字段，我需要将它转换为 ManyToManyField。当我运行迁移时，它给出了这个错误：

ValueError：无法将字段 core_app.IndieTrack.contributors 更改为 core_app.IndieTrack.contributors - 它们不是兼容的类型（你 无法更改 M2M 字段或从 M2M 字段更改，或通过 = 在 M2M 上添加或删除 字段）

所以我说，“好吧”，然后我将它恢复为 ForeignKey，我想我会想出一个替代解决方案。但是当我再次迁移（回到原始状态）时，它给了我同样的错误。

现在我根本无法迁移任何更改。不管我做什么，我都会得到同样的错误。

这是整个追溯：

python3.4 manage.py makemigrations core_app              Migrations for 'core_app':
  0034_auto_20150521_0740.py:
    - Create model UserTrack
    - Remove field contributors from indietrack
    - Delete model IndieTrack
    - Alter field tracks on album
python3.4 manage.py migrate
Operations to perform:
  Apply all migrations: sessions, home, auth, admin, ipn, beat_store, blog, core    _app, contenttypes
Running migrations:
  Applying core_app.0024_auto_20150521_0634...Traceback (most recent call last):

Running migrations:
  Applying core_app.0024_auto_20150521_0634...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/base.py", line 533, in handle
    return self.handle_noargs(**options)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/commands/syncdb.py", line 27, in handle_noargs
    call_command("migrate", **options)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/__init__.py", line 115, in call_command
    return klass.execute(*args, **defaults)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/core/management/commands/migrate.py", line 161, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/db/migrations/executor.py", line 68, in migrate
    self.apply_migration(migration, fake=fake)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/db/migrations/executor.py", line 102, in apply_migration
    migration.apply(project_state, schema_editor)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/db/migrations/migration.py", line 108, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/db/migrations/operations/fields.py", line 139, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/home/thephltr/webapps/who_pro/lib/python3.4/Django-1.7.7-py3.4.egg/django/db/backends/schema.py", line 454, in alter_field
    new_field,
ValueError: Cannot alter field core_app.IndieTrack.contributors into core_app.IndieTrack.contributors - they are not compatible types (you cannot alter to or from M2M fields, or add or remove through= on M2M fields)

这是我的模型：

class IndieTrack(models.Model):
    duration = models.CharField(max_length=12, default='0:00')
    track_title = models.CharField(max_length=95)
    track_number = models.IntegerField(default=0)
    contributors = models.ForeignKey(Artist, null=True, blank=True)
    extra_info = models.TextField(null=True, blank=True)

    def __str__(self):
        return self.track_title

我需要做出一些改变。任何见解将不胜感激。

我正在使用 PostgreSQL

Answer 1

如果该字段是您更改的全部内容，我建议您返回迁移文件夹并删除在您尝试将其更改为多对多字段后创建的那些。由于您已经创建了上述迁移，并且 Django 按顺序运行它们，因此它将继续尝试运行它，因为您之后所做的迁移依赖于它，并且该错误将继续出现。当我自己的理智发生这种情况时，我就是这样做的。

如果您更改了其他字段，也许您可​​以输入该迁移文件并删除与该字段相关的位。