Django 1.7：惰性评估以避免 "App registry isn't ready yet" in models.py
Django 1.7: Lazy evaluation to avoid "App registry isn't ready yet" in models.py
我在模型的方法定义中有一个查询：
'content_type_id': ContentType.objects.get_for_model(model).pk,
https://github.com/seperman/django-tagging/blob/develop/tagging/models.py#L107
它会引发 "App registry is not ready yet"。
将这一行放在另一个独立的函数中也无济于事，因为它仍然会被调用。
Django 文档：
Executing database queries with the ORM at import time in models
modules will also trigger this exception. The ORM cannot function
properly until all models are available.
如何让它懒惰地评估这一行？
我考虑过通过管理命令将其结果手动缓存在一个文件中。然后读取缓存的结果但是应该有很多better/cleaner解决方案(?)
./manage.py shell
Traceback (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), False
File "/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。
您在应用程序注册之前调用 _get_usage。无论您在哪里调用它，都需要将其更改为已配置应用程序的位置。基本上，如果您在导入时需要模型，您应该使用 ready().
例如，如果您有一个 signals.py，您可以这样做：
# in apps.py
class SomeAppConfig(AppConfig):
def ready(self):
from . import signals
或者您的情况：
# in apps.py
class SomeAppConfig(AppConfig):
def ready(self):
mgr = TagManager()
mgr._get_usage(#some_args)
如文档所述：ready() ... is called as soon as the registry is fully populated
django 标记在这里有点不体贴。
TagField is a descriptor，这意味着如果您访问 YourModel.tags，它会运行执行数据库查询的代码。
碰巧 django-mptt 在启动期间（在加载应用程序缓存之前）遍历了 MPTTModel 类 的所有属性，因此恰好触发了此异常。
我不知道你如何在维护 API 的同时在 django 标记中防止这种情况（YourModel.tags 必须从 某处获取标签 ).像这样的问题可能是 django-tagging 不再维护的原因。
但是，我是 django-mptt 的维护者并且我committed a workaround。如果您升级到 mptt 的主版本，您应该会发现它现在可以工作了。
我在模型的方法定义中有一个查询：
'content_type_id': ContentType.objects.get_for_model(model).pk,
https://github.com/seperman/django-tagging/blob/develop/tagging/models.py#L107
它会引发 "App registry is not ready yet"。
将这一行放在另一个独立的函数中也无济于事，因为它仍然会被调用。
Django 文档：
Executing database queries with the ORM at import time in models modules will also trigger this exception. The ORM cannot function properly until all models are available.
如何让它懒惰地评估这一行？ 我考虑过通过管理命令将其结果手动缓存在一个文件中。然后读取缓存的结果但是应该有很多better/cleaner解决方案(?)
./manage.py shell
Traceback (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), False
File "/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。
您在应用程序注册之前调用 _get_usage。无论您在哪里调用它，都需要将其更改为已配置应用程序的位置。基本上，如果您在导入时需要模型，您应该使用 ready().
例如，如果您有一个 signals.py，您可以这样做：
# in apps.py
class SomeAppConfig(AppConfig):
def ready(self):
from . import signals
或者您的情况：
# in apps.py
class SomeAppConfig(AppConfig):
def ready(self):
mgr = TagManager()
mgr._get_usage(#some_args)
如文档所述：ready() ... is called as soon as the registry is fully populated
django 标记在这里有点不体贴。
TagField is a descriptor，这意味着如果您访问 YourModel.tags，它会运行执行数据库查询的代码。
碰巧 django-mptt 在启动期间（在加载应用程序缓存之前）遍历了 MPTTModel 类 的所有属性，因此恰好触发了此异常。
我不知道你如何在维护 API 的同时在 django 标记中防止这种情况（YourModel.tags 必须从 某处获取标签 ).像这样的问题可能是 django-tagging 不再维护的原因。
但是，我是 django-mptt 的维护者并且我committed a workaround。如果您升级到 mptt 的主版本，您应该会发现它现在可以工作了。