'NoneType' 对象在 Django 迁移中没有属性 'is_relation' 错误答案

【问题标题】：'NoneType' object has no attribute 'is_relation' error on Django Migrations'NoneType' 对象在 Django 迁移中没有属性 'is_relation' 错误
【发布时间】：2019-03-05 01:05:43
【问题描述】：

我正在尝试从 Heroku 上现有的 Django 模型中删除一些字段，所以我运行 make 迁移，然后 migrate 命令，看起来迁移成功了。

之后我发现缺少一个字段，所以我自己创建了下一个迁移文件，将依赖项放在上一个自动生成的迁移文件中。当我运行它时，我有一个这样的错误：

~ $ python manage.py migrate
Operations to perform:
  Apply all migrations: API, admin, auth, authtoken, contenttypes, sessions
Running migrations:
  Applying API.0007_timezoneremoval...Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
    utility.execute()
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/migration.py", line 119, in apply
    operation.state_forwards(self.app_label, project_state)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/operations/fields.py", line 150, in state_forwards
    delay = not old_field.is_relation
AttributeError: 'NoneType' object has no attribute 'is_relation'

这个错误可能是从哪里引起的？谢谢

【问题讨论】：

old_field 来自哪里，它就是None。请包含显示变量如何初始化的代码。
变量在哪里初始化？我应该提供模型还是迁移代码？
请同时提供

标签： python django postgresql heroku django-rest-framework

【解决方案1】：

您可以进入migrate文件夹，删除除__init__.py之外的所有.py文件。

之后，运行：

python manage.py makemigrations

【讨论】：