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django - django db ProgrammingError

问题描述

当我尝试重置数据库时（我创建了一个新的空数据库）

当我运行这个命令python manage.pymakemigrations（或迁移）时出现这个错误

    for pattern in self.url_patterns:
  File "django\utils\functional.py", line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "django\urls\resolvers.py", line 589, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "django\utils\functional.py", line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "django\urls\resolvers.py", line 582, in urlconf_module
    return import_module(self.urlconf_name)
  File \python\python39\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "project\urls.py", line 18, in <module>
    path('api/v2/', include('project.api.urls'), name='api'),
  File "django\urls\conf.py", line 34, in include
    urlconf_module = import_module(urlconf_module)
  File "python\python39\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "project\api\urls.py", line 3, in <module>
    from .views import *
  File "project\api\views.py", line 146, in <module>
    class SampleViewSet(viewsets.ModelViewSet):
  File "project\api\views.py", line 148, in SampleViewSet
    general = General.objects.get(is_active=True)
  File "django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "django\db\models\query.py", line 425, in get
    num = len(clone)
  File "django\db\models\query.py", line 269, in __len__
    self._fetch_all()
  File "django\db\models\query.py", line 1308, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "django\db\models\query.py", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "django\db\models\sql\compiler.py", line 1156, in execute_sql
    cursor.execute(sql, params)
  File "django\db\backends\utils.py", line 98, in execute
    return super().execute(sql, params)
  File "django\db\backends\utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "django\db\backends\utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "env\lib\site-packages\django\db\utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "env\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
        django.db.utils.ProgrammingError: HATA:  "app_general" object doesnt exist
    LINE 1: ...", "app_general"."field1" FROM "field_2...

视图.py

class SampleViewSet(viewsets.ModelViewSet):
    general = General.objects.get(is_active=True)
    queryset = model.objects.filter(field=site_general.field)

我删除了所有应用程序中的所有迁移文件（没有 __init__）以及 .pyc 文件

这个问题有什么想法吗？

（编辑我添加了 Traceback）

标签： djangodjango-models

解决方案

类的所有非方法属性在类的声明或定义期间被评估/执行。因此，当解释器到达您的类时SampleViewSet，它会尝试执行该行general = General.objects.get(is_active=True)，但您的数据库当然还不存在，并且由于调用.get意味着数据库查询，您会收到错误。

一般来说，任何可能导致数据库查询的语句都应该由应用程序配置ready方法、某些中间件/上下文处理器或请求中的视图运行。查看代码，它看起来不像你general在任何地方使用，所以你可以简单地删除它：

class SampleViewSet(viewsets.ModelViewSet):
    queryset = model.objects.filter(field=site_general.field)

您可能会说model.objects.filter(...)也会导致查询，但.filter返回 aQuerySet和查询集是惰性的，因此仅在需要时才进行评估，因此不会导致任何错误。

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