Django 1.7：懒惰的评估，以避免“应用程序注册表尚未准备好”在models.py

本文介绍了Django 1.7：懒惰的评估，以避免“应用程序注册表尚未准备好”在models.py的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我在模型的方法定义中有一个查询：I have a query in a model's method definition:'content_type_id': ContentType.objects.get_for_model(model).pk, https://github.com/seperman/django-tagging/blob/develop/tagging/models.py#L107 它引发了应用程序注册表尚未准备好。And it raises "App registry is not ready yet".将行放在另一个独立的函数中没有帮助因为它仍然被调用。 Putting the line inside another independent function doesn't help either since it still gets called. Django文档：如何让它懒惰评估这一行？ 我想到通过管理命令将其结果手动缓存到文件中。然后阅读缓存的结果，但应该有一个更好/更清洁的解决方案（？）How can I make it lazy evaluate this line?I thought about caching its results manually in a file by making a management command. And then reading the cached result but there should be a much better/cleaner solution(?)./manage.py shellTraceback (most recent call last):File "./manage.py", line 10, in <module> execute_from_command_line(sys.argv)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line utility.execute()File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 354, in execute django.setup()File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/__init__.py", line 21, in setup apps.populate(settings.INSTALLED_APPS)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/apps/registry.py", line 108, in populate app_config.import_models(all_models)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/apps/config.py", line 202, in import_models self.models_module = import_module(models_module_name)File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module __import__(name)File "/var/www/something.com/something/current/apps/riding/models.py", line 32, in <module> class RidingSection(CategoryBase):File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/mptt/models.py", line 244, in __new__ cls = meta.register(cls)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/mptt/models.py", line 325, in register obj = getattr(cls, attr)File "/var/www/something.com/something/current/apps/tagging/fields.py", line 54, in __get__ return edit_string_for_tags(Tag.objects.usage_for_model(owner))File "/var/www/something.com/something/current/apps/tagging/models.py", line 148, in usage_for_model usage = self.usage_for_queryset(queryset, counts, min_count)File "/var/www/something.com/something/current/apps/tagging/models.py", line 185, in usage_for_queryset return self._get_usage(queryset.model, counts, min_count, extra_joins, extra_criteria, params)File "/var/www/something.com/something/current/apps/tagging/models.py", line 107, in _get_usage 'content_type_id': ContentType.objects.get_for_model(model).pk,File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/contrib/contenttypes/models.py", line 50, in get_for_model defaults={'name': smart_text(opts.verbose_name_raw)},File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/manager.py", line 92, in manager_method return getattr(self.get_queryset(), name)(*args, **kwargs)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 422, in get_or_create return self.get(**lookup), FalseFile "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 345, in get clone = self.filter(*args, **kwargs)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 691, in filter return self._filter_or_exclude(False, *args, **kwargs)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 709, in _filter_or_exclude clone.query.add_q(Q(*args, **kwargs))File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1287, in add_q clause, require_inner = self._add_q(where_part, self.used_aliases)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1314, in _add_q current_negated=current_negated, connector=connector)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1138, in build_filter lookups, parts, reffed_aggregate = self.solve_lookup_type(arg)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1076, in solve_lookup_type _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1339, in names_to_path field, model, direct, m2m = opts.get_field_by_name(name)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/options.py", line 416, in get_field_by_name cache = self.init_name_map()File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/options.py", line 445, in init_name_map for f, model in self.get_all_related_m2m_objects_with_model():File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/options.py", line 563, in get_all_related_m2m_objects_with_model cache = self._fill_related_many_to_many_cache()File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/db/models/options.py", line 577, in _fill_related_many_to_many_cache for klass in self.apps.get_models():File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/utils/lru_cache.py", line 101, in wrapper result = user_function(*args, **kwds)File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/apps/registry.py", line 168, in get_models self.check_models_ready()File "/var/www/something.com/something/shared/env/local/lib/python2.7/site-packages/django/apps/registry.py", line 131, in check_models_ready raise AppRegistryNotReady("Models aren't loaded yet.") django.core.exceptions.AppRegistryNotReady：模型尚未加载。django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.推荐答案 django-tagging在这里有点不明智。django-tagging is being a little inconsiderate here. TagField是一个描述符，这意味着如果您访问 YourModel.tags ，它运行执行数据库查询的代码。TagField is a descriptor, meaning if you access YourModel.tags, it runs code which executes a database query.只是这样，django-mptt迭代在启动期间（在应用程序缓存加载之前），您的MPTTModel类的所有属性，因此触发此异常。It just so happens that django-mptt iterates over all the attributes of your MPTTModel classes during startup (before the app cache has loaded), so it happens to trigger this exception.我不知道你会防止在django标记中维护API（ YourModel.tags 必须从 中获取标签）。这样的问题可能是django-tagging不再维护的原因。I don't know how you'd prevent that in django-tagging while maintaining the API (YourModel.tags has to get tags from somewhere). Issues like this are probably the reason why django-tagging is no longer maintained.但是，我是django-mptt的维护者，我有提交了解决方法。如果您升级到主版本的mptt，您应该会发现它现在可以工作。However, I'm the maintainer of django-mptt and I've committed a workaround. If you upgrade to the master version of mptt you should find it works now. 这篇关于Django 1.7：懒惰的评估，以避免“应用程序注册表尚未准备好”在models.py的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！