天天短讯！Django的message组件(源码分析)

2023-04-30 11:28:00来源：博客园

(资料图片)

Django的Message组件(源码分析)1. 配置

# MESSAGE_STORAGE = "django.contrib.messages.storage.fallback.FallbackStorage"# MESSAGE_STORAGE = "django.contrib.messages.storage.cookie.CookieStorage"MESSAGE_STORAGE = "django.contrib.messages.storage.session.SessionStorage"

INSTALLED_APPS = [    # "django.contrib.admin",    # "django.contrib.auth",    # "django.contrib.contenttypes",    # "django.contrib.sessions",    "django.contrib.messages",  # 配置    "django.contrib.staticfiles",    "web.apps.WebConfig"]

MIDDLEWARE = [    "django.middleware.security.SecurityMiddleware",    "django.contrib.sessions.middleware.SessionMiddleware",    "django.middleware.common.CommonMiddleware",    "django.middleware.csrf.CsrfViewMiddleware",    # "django.contrib.auth.middleware.AuthenticationMiddleware",    "django.contrib.messages.middleware.MessageMiddleware",  # 中间件    "django.middleware.clickjacking.XFrameOptionsMiddleware",    "utils.md.AuthMiddleware"]

TEMPLATES = [    {        "BACKEND": "django.template.backends.django.DjangoTemplates",        "DIRS": [],        "APP_DIRS": True,        "OPTIONS": {            "context_processors": [                "django.template.context_processors.debug",                "django.template.context_processors.request",                # "django.contrib.auth.context_processors.auth",                "django.contrib.messages.context_processors.messages",            ],        },    },]

2. 设置值

from django.contrib import messagesmessages.add_message(reqeust, messages.SUCCESS, "删除成功1")messages.add_message(reqeust, messages.ERROR, "操作失败")

3. 读取值第一种: 视图中读取

from django.contrib.messages.api import get_messagesmessages = get_messages(request)for msg in messages:    print(msg)

第二种: 模版中读取

    {% for message in messages %}    {{ message.tags }} {{ message }}
    {% endfor %}

4. 源码分析4.1第一步: 设置值

from django.contrib import messagesmessages.add_message(reqeust, messages.SUCCESS, "删除成功1")

我们根据django的生命周期, 从Middleware入手,

process_request: 将SessionStorage对象封装到request的_message(咱们的案例里面也有将用户信息封装到request中, 这样在中间件中添加方便后期调用)process_response: 将message对象反序列化后储存到session/Cookie中4.2 第二步: 读取值process_request: 通过循环读取message内容process_response: 从session中删除message值

【设置】中间件process_request加载

【设置】在视图函数中往message中写入值（内存）

【设置】中间件process_response，将内存中新增的数据写入到数据源

【新页面】中间件process_request加载

【新页面】在视图函数或模板中读取message中的信息（老的数据源加载的+新增的）

【设置】中间件process_response

used = True，则只保存新增部分。added_new = True，老的数据源加载的+新增的都重新保存到数据源。

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