Apps 源码分析
Apps 下主要有两个类: AppConfig和Apps.
目录结构
apps/ # 应用目录
├── __init__.py # 应用初始化文件
├── config.py # AppConfig 类
├── registry.py # Apps 类
AppConfig
位于 apps/config.py 文件中, 主要用来定义应用的配置信息和初始化过后的过程函数。
属性
name: 应用的名称, 一般是应用的包名.module: 应用的模块, 一般是应用的__init__.py文件.apps: 应用管理器, 用来管理应用的注册和配置信息.label: 应用的标签, 包名的最后一部分, 如django.contrib.admin=>admin.verbose_name: 应用的显示名称, 一般是应用的名称的首字母大写形式.path: 应用的路径, 一般是应用的包路径.models_module: 应用的模型模块, 通过import_models加载，在 app 初始化完成前，该属性为None.models: 应用的模型 mapping[str, models.Model], 通过import_models加载，在 app 初始化完成前，该属性为None.
重要函数
create(): 类方法，返回一个AppConfig实例，通过外部的 entry 字符串，加载目录下的 apps 中的子类并初始化返回，可以通过设置default属性来控制实例化哪个AppConfig子类。
class AppConfig:...@classmethoddef create(cls, entry):"""Factory that creates an app config from an entry in INSTALLED_APPS."""# create() eventually returns app_config_class(app_name, app_module).app_config_class = Noneapp_name = Noneapp_module = None# If import_module succeeds, entry points to the app module.try:app_module = import_module(entry)except Exception:passelse:# If app_module has an apps submodule that defines a single# AppConfig subclass, use it automatically.# To prevent this, an AppConfig subclass can declare a class# variable default = False.# If the apps module defines more than one AppConfig subclass,# the default one can declare default = True.if module_has_submodule(app_module, APPS_MODULE_NAME):mod_path = "%s.%s" % (entry, APPS_MODULE_NAME)mod = import_module(mod_path)# Check if there's exactly one AppConfig candidate,# excluding those that explicitly define default = False.app_configs = [(name, candidate)for name, candidate in inspect.getmembers(mod, inspect.isclass)if (issubclass(candidate, cls)and candidate is not clsand getattr(candidate, "default", True))]if len(app_configs) == 1:app_config_class = app_configs[0][1]else:# Check if there's exactly one AppConfig subclass,# among those that explicitly define default = True.app_configs = [(name, candidate)for name, candidate in app_configsif getattr(candidate, "default", False)]if len(app_configs) > 1:candidates = [repr(name) for name, _ in app_configs]raise RuntimeError("%r declares more than one default AppConfig: ""%s." % (mod_path, ", ".join(candidates)))elif len(app_configs) == 1:app_config_class = app_configs[0][1]# Use the default app config class if we didn't find anything.if app_config_class is None:app_config_class = clsapp_name = entry# If import_string succeeds, entry is an app config class.if app_config_class is None:try:app_config_class = import_string(entry)except Exception:pass# If both import_module and import_string failed, it means that entry# doesn't have a valid value.if app_module is None and app_config_class is None:# If the last component of entry starts with an uppercase letter,# then it was likely intended to be an app config class; if not,# an app module. Provide a nice error message in both cases.mod_path, _, cls_name = entry.rpartition(".")if mod_path and cls_name[0].isupper():# We could simply re-trigger the string import exception, but# we're going the extra mile and providing a better error# message for typos in INSTALLED_APPS.# This may raise ImportError, which is the best exception# possible if the module at mod_path cannot be imported.mod = import_module(mod_path)candidates = [repr(name)for name, candidate in inspect.getmembers(mod, inspect.isclass)if issubclass(candidate, cls) and candidate is not cls]msg = "Module '%s' does not contain a '%s' class." % (mod_path,cls_name,)if candidates:msg += " Choices are: %s." % ", ".join(candidates)raise ImportError(msg)else:# Re-trigger the module import exception.import_module(entry)# Check for obvious errors. (This check prevents duck typing, but# it could be removed if it became a problem in practice.)if not issubclass(app_config_class, AppConfig):raise ImproperlyConfigured("'%s' isn't a subclass of AppConfig." % entry)# Obtain app name here rather than in AppClass.__init__ to keep# all error checking for entries in INSTALLED_APPS in one place.if app_name is None:try:app_name = app_config_class.nameexcept AttributeError:raise ImproperlyConfigured("'%s' must supply a name attribute." % entry)# Ensure app_name points to a valid module.try:app_module = import_module(app_name)except ImportError:raise ImproperlyConfigured("Cannot import '%s'. Check that '%s.%s.name' is correct."% (app_name,app_config_class.__module__,app_config_class.__qualname__,))# Entry is a path to an app config class.return app_config_class(app_name, app_module)ready(): 实例方法，在应用初始化完成后调用，一般用来注册信号和其他初始化操作。
Apps
属性
all_models: 存放app_label.model_name和Model的 mapping, 在 Model.new中调用apps.register_model完成注册。app_configs: 存放AppConfig实例的 mapping。stored_app_configs: 栈存放当前状态apps_ready: 标志位，表示是否已经完成应用初始化。models_ready: 标志位，表示是否已经完成模型初始化。ready: 标志位，表示是否已经完成初始化。_lock: 锁，用来控制并发访问。loading: 标志位，表示是否正在加载。_pending_operations: 存放延迟 Model 注册的操作。应对模型的关联问题。
重要函数
populate(): 实例方法,
- 根据传入的
installed_apps遍历初始化应用，如果已经是 AppConfig,则直接使用；否则调用create方法创建.将初始化完成的 AppConfig 实例存入app_configs中。在此确保app 名字不允许重复。
# Phase 1: initialize app configs and import app modules.
for entry in installed_apps:if isinstance(entry, AppConfig):app_config = entryelse:app_config = AppConfig.create(entry)# 不能重名if app_config.label in self.app_configs:raise ImproperlyConfigured("Application labels aren't unique, ""duplicates: %s" % app_config.label)self.app_configs[app_config.label] = app_configapp_config.apps = self# Check for duplicate app names.
# 可以用counter来统计重复
counts = Counter(app_config.name for app_config in self.app_configs.values()
)
duplicates = [name for name, count in counts.most_common() if count > 1]
if duplicates:raise ImproperlyConfigured("Application names aren't unique, ""duplicates: %s" % ", ".join(duplicates))
- 初始化各应用的模型
# Phase 2: import models modules.
for app_config in self.app_configs.values():app_config.import_models()self.clear_cache()self.models_ready = True
- 完成初始化
# Phase 3: run ready() methods of app configs.
for app_config in self.get_app_configs():# 调用每个appconfig的ready方法,完成自定义初始化步骤app_config.ready()self.ready = True
self.ready_event.set()
get_models(): 实例方法，返回所有注册的模型列表，带缓存。
# This method is performance-critical at least for Django's test suite.
@functools.cache
def get_models(self, include_auto_created=False, include_swapped=False):"""Return a list of all installed models.By default, the following models aren't included:- auto-created models for many-to-many relations withoutan explicit intermediate table,- models that have been swapped out.Set the corresponding keyword argument to True to include such models."""self.check_models_ready()result = []for app_config in self.app_configs.values():result.extend(app_config.get_models(include_auto_created, include_swapped))return result
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