Django：Model.objects.get 失败，出现 ImportError 异常

Question

我有一个模型，它代表了我系统中的设置，我在应用程序的其他部分使用这个模型，所以导入的层级有3个：工作代码 <- 模块 <- 模型

模型中的变量

from django.db import models

class Variables(models.Model):
    key = models.CharField(max_length = 20, verbose_name = 'Variable')
    value = models.CharField(max_length = 1024)

    class Meta:
        app_label = 'core'

    def __unicode__(self):
        return '%s: %s' % (self.key, self.value,)

这是我使用的代码

模块variables.py

from core.models.storage import Variables

def get_var(name):
  return Variables.objects.get(key = name)

模块config.py

  var = get_var('some_key')

当我在django的命令行中使用这些东西时，一切都运行得很好，但当我调用get_var函数时，我遇到了ImportError异常

storage.py

from django.db import models

class Variables(models.Model):
    key = models.CharField(max_length = 20, verbose_name = 'Variable')
    value = models.CharField(max_length = 1024)

    class Meta:
        app_label = 'core'

    def __unicode__(self):
        return '%s: %s' % (self.key, self.value,)

  File "monitor_cli.py", line 19, in 
    print worker.get_provider()
  File "/home/sultan/Project/monitor/app/worker.py", line 14, in get_provider
    print Variables.objects.get(pk=1)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/manager.py", line 132, in get
    return self.get_query_set().get(*args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 341, in get
    clone = self.filter(*args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 550, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 568, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1172, in add_q
    can_reuse=used_aliases, force_having=force_having)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1060, in add_filter
    negate=negate, process_extras=process_extras)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1226, in setup_joins
    field, model, direct, m2m = opts.get_field_by_name(name)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/options.py", line 307, in get_field_by_name
    cache = self.init_name_map()
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/options.py", line 337, in init_name_map
    for f, model in self.get_all_related_m2m_objects_with_model():
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/options.py", line 414, in get_all_related_m2m_objects_with_model
    cache = self._fill_related_many_to_many_cache()
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/options.py", line 428, in _fill_related_many_to_many_cache
    for klass in get_models():
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/loading.py", line 167, in get_models
    self._populate()
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/loading.py", line 61, in _populate
    self.load_app(app_name, True)
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/loading.py", line 76, in load_app
    app_module = import_module(app_name)
  File "/usr/local/lib/python2.6/dist-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
ImportError: No module named c

Answer 1

把模型目录删掉，把所有的模型放到一个叫 models.py 的文件里，除非你有非常好的理由不这样做。把你的导入语句改成 from core.models import Variable（把你的 Variables 类改名为 Variable - django 的模型应该用单数形式，而不是复数）。

问题可能出在你的模型放在了其他命名空间里，比如 models.storage。django 的框架期望某些东西在特定的位置。如果你要把模型放在像你这样不同的命名空间里，你应该从 models 模块里的 __init__.py 文件导入它们。除非你有很好的理由，否则不要这样做。

最后，当你问这种问题时，应该提供更多的信息。你需要展示所有相关文件的代码。还要详细说明你做了哪些与 django 的约定不同的事情（在这个例子中，就是用模型目录而不是 models.py 文件）。你还应该展示 settings.py 中相关的设置，比如你的 INSTALLED_APPS 设置。还要告诉我们你使用的 django 和 python 的版本；这有时是很重要的。提供更多的信息总比提供少的信息要好。