在 Django 中更改 ManyToMany 字段时，我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: 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)

所以我说，"fine," 然后我将它还原为 ForeignKey，我想我会想出一个替代解决方案。但是当我再次迁移（回到原来的状态）时，它给了我同样的错误。

现在我根本无法迁移任何更改。无论我做什么，我都会得到同样的错误。

这是整个回溯：

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

我需要进行更改。任何见解将不胜感激。

我正在使用 PostgreSQL

Answer 1

如果您仅更改了该字段，我建议您返回迁移文件夹并删除在尝试将其更改为 ManytoMany 字段后创建的那些。由于您已经创建了上述迁移，并且 Django 运行按顺序对它们进行了排序，因此它将继续尝试运行它，因为您之后进行的迁移取决于它并且该错误将继续存在出现。当这种情况发生时，为了我自己的理智，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。

在 Django 中更改 ManyToMany 字段时，我是否破坏了我的数据库？

Did I break my DB while changing ManyToMany field in Django?

python

django

postgresql

manytomanyfield