Session

Session的使用一般依赖于Cookie，将一些数据不再发送值浏览器，而是保存的后端的服务器上。

1 使用

• Session到底要存储到哪里？默认数据库。

  INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      # 'django.contrib.sessions',     # sessions功能的APP    django_session
      'django.contrib.messages',
      'django.contrib.staticfiles',
  ]
  

  MIDDLEWARE = [
      'django.middleware.security.SecurityMiddleware',
      'django.contrib.sessions.middleware.SessionMiddleware', # process_request/process_response
      'django.middleware.common.CommonMiddleware',
      'django.middleware.csrf.CsrfViewMiddleware',
      'django.contrib.auth.middleware.AuthenticationMiddleware',
      'django.contrib.messages.middleware.MessageMiddleware',
      'django.middleware.clickjacking.XFrameOptionsMiddleware',
      # "utils.md.KeLaMiddleware",
  ]
  

  ############
  # SESSIONS #
  ############
  # Session存储在哪里？
  SESSION_ENGINE = "django.contrib.sessions.backends.db"
  
  # 如果存储到文件中，文件的路径。
  SESSION_ENGINE = "django.contrib.sessions.backends.file"
  SESSION_FILE_PATH = None
  
  # 存储到缓存
  SESSION_ENGINE = "django.contrib.sessions.backends.cache"
  SESSION_CACHE_ALIAS = "default"
  
  
  # 存储到缓存 + 数据库
  SESSION_ENGINE = "django.contrib.sessions.backends.cache_db"
  SESSION_CACHE_ALIAS = "default"
  
  # 存储到cookie
  SESSION_ENGINE = "django.contrib.sessions.backends.signed_cookies"
  
  # class to serialize session data
  SESSION_SERIALIZER = "django.contrib.sessions.serializers.JSONSerializer"
  
  
  # -------------------------------
  # Cookie name. This can be whatever you want.
  SESSION_COOKIE_NAME = "sessionid"
  # Age of cookie, in seconds (default: 2 weeks).
  SESSION_COOKIE_AGE = 60 * 60 * 24 * 7 * 2
  # A string like "example.com", or None for standard domain cookie.
  SESSION_COOKIE_DOMAIN = None
  # Whether the session cookie should be secure (https:// only).
  SESSION_COOKIE_SECURE = False
  # The path of the session cookie.
  SESSION_COOKIE_PATH = "/"
  # Whether to use the HttpOnly flag.
  SESSION_COOKIE_HTTPONLY = True
  # Whether to set the flag restricting cookie leaks on cross-site requests.
  # This can be 'Lax', 'Strict', 'None', or False to disable the flag.
  SESSION_COOKIE_SAMESITE = "Lax"
  # Whether to save the session data on every request.
  SESSION_SAVE_EVERY_REQUEST = False
  # Whether a user's session cookie expires when the web browser is closed.
  SESSION_EXPIRE_AT_BROWSER_CLOSE = False
  

  注意：如果是非数据库，可以主调用app的注册代码部分。

• 请求=登录，生成Session、Cookie。

• 再次请求，默认携带cookie，根据Cookie中的凭证，去找到Session中原本存储的数据。

  request.session['id'] = 999
  request.session['id'] = 88
  request.session.get("id")
  
  # del request.session['id']
  # request.session.clear()
  

  from django.urls import path
  from django.shortcuts import HttpResponse
  
  def x1(request):
      request.session['id'] = 999
      request.session['name'] = 'wupeiqi'
      request.session['age'] = '25'
      return HttpResponse("x1")
  
  def x2(request):
      print(request.session.get("id"))
      print(request.session.get("name"))
      print(request.session.get("age"))
  
      return HttpResponse("x2")
  
  urlpatterns = [
      path('x1/', x1, name='x1'),
      path('x2/', x2, name='x2'),
  ]
  

2 源码

1.引擎配置

• 数据库引擎

  SESSION_ENGINE = "django.contrib.sessions.backends.db"
  

  INSTALLED_APPS = [
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
  ]
  

  >>>python manage.py makemigrations
  >>>python manage.py migrate
  

• 文件

  # 如果存储到文件中，文件的路径。
  SESSION_ENGINE = "django.contrib.sessions.backends.file"
  SESSION_FILE_PATH = None
  

  INSTALLED_APPS = [
      #'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
  ]
  

2.中间件

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',  # 必须设置
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
	...
]

2.1 创建对象

在启动django程序时，会自动创建 SessionMiddlewared对象。

class MiddlewareMixin:

    def __init__(self, get_response):
        self.get_response = get_response

class SessionMiddleware(MiddlewareMixin):
    def __init__(self, get_response):
        super().__init__(get_response)

        # "django.contrib.sessions.backends.db"   "django.contrib.sessions.backends.file"
        engine = import_module(settings.SESSION_ENGINE)

        # db.SessionStore    file.SessionStore
        self.SessionStore = engine.SessionStore

2.2 请求到来 *

def process_request(self, request):
    # 1.去Cookie中读取凭证 mid="123123123123"
    session_key = request.COOKIES.get(settings.SESSION_COOKIE_NAME)
    # 2.实例化
    request.session = self.SessionStore(session_key)

def x1(request):
	# request.session -> file.SessionStore() / 
    
    
    request.session['id'] = 999
    request.session['name'] = 'wupeiqi'    类中的__setitem__
    request.session['age'] = '25'

    return HttpResponse("x1")

2.3 请求结束 *

...