Django 迁移因新数据库而失败

Question

想知道是否有其他人在使用 Django 迁移时遇到令人沮丧的行为。我查看了 SO 上的几篇相关帖子，但没有找到任何具体解决此问题的内容。

我经常遇到这种情况，这一定是一种常见的情况，所以我错过了什么？

我的场景：

列表项
我构建了一个 Django 应用程序，在我的本地计算机上使用 sqlite 进行迭代
我现在想部署到生产 Postgresql 数据库（AWS 或其他地方）
我设置了我的新数据库，将其添加到我的设置中，然后运行 python manage.py migrate
我收到一个 SQL 错误，告诉我我的模型表之一不存在。呸！这就是我要运行迁移的原因。
我最终不得不手工制作表格，做一些奇怪的事情，比如 python manage.py migrate <app_name> --fake，这给 simple_history

我相信肯定有一个明显的答案——我应该怎么做才能在一个全新的、干净的数据库上设置数据库模式？

编辑：我得到的错误回溯：

当我在空白数据库上运行 python manage.py migrate 时，出现以下错误：

(banzai-platform-django) ➜  src git:(master) ✗ ./manage.py migrate
Traceback (most recent call last):
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: relation "events_event" does not exist
LINE 1: ...ents_event"."created", "events_event"."slug" FROM "events_ev...
                                                             ^


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "./manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line
    utility.execute()
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/__init__.py", line 355, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/base.py", line 327, in execute
    self.check()
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/base.py", line 359, in check
    include_deployment_checks=include_deployment_checks,
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 62, in _run_checks
    issues.extend(super(Command, self)._run_checks(**kwargs))
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/management/base.py", line 346, in _run_checks
    return checks.run_checks(**kwargs)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/checks/registry.py", line 81, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/checks/urls.py", line 16, in check_url_config
    return check_resolver(resolver)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/core/checks/urls.py", line 26, in check_resolver
    return check_method()
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/urls/resolvers.py", line 254, in check
    for pattern in self.url_patterns:
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/urls/resolvers.py", line 405, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/urls/resolvers.py", line 398, in urlconf_module
    return import_module(self.urlconf_name)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 978, in _gcd_import
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 655, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 205, in _call_with_frames_removed
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/src/banzai_platform/urls.py", line 67, in <module>
    url(r'^registrations/', include('registrations.urls')),
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/conf/urls/__init__.py", line 50, in include
    urlconf_module = import_module(urlconf_module)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 978, in _gcd_import
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 655, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 205, in _call_with_frames_removed
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/src/registrations/urls.py", line 3, in <module>
    from .views import (
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/src/registrations/views.py", line 160, in <module>
    class ConfirmEventListView(ListView):
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/src/registrations/views.py", line 164, in ConfirmEventListView
    queryset = [obj for obj in events if obj.need_confirmation > 0]
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/models/query.py", line 250, in __iter__
    self._fetch_all()
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/models/query.py", line 1118, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/models/query.py", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 894, in execute_sql
    raise original_exception
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 884, in execute_sql
    cursor.execute(sql, params)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/backends/utils.py", line 80, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/Users/joedavy/Dropbox/Apps/banzai-platform-django/lib/python3.6/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "events_event" does not exist
LINE 1: ...ents_event"."created", "events_event"."slug" FROM "events_ev...

Answer 1

您的回溯显示您正在运行在 ConfirmEventListView 中 class 级别对查询集进行列表理解。 class 级别的任何内容在首次导入 class 时执行；所以这个查询是在执行任何 Django 命令时立即完成的，这是在迁移有机会运行.

之前

您绝不能在此级别上执行任何访问数据库的操作。（老实说，你根本不应该做这个列表理解，因为它返回的是一个列表而不是一个查询集；所以它不适用于分页或其他需要实际查询集的东西。但是，因为你的其余部分代码有效，我们可以假设这在您的情况下还不是问题。）

如果 need_confirmation 是一个字段，您的查询集应该定义为 Event.objects.filter(need_confirmation__gt=0)。但是，如果它是一个模型方法，那么您应该在 ConfirmEventListView 上定义一个 get_queryset() 方法并在那里执行此处理，而不是在 class 级别。

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