Django登录状态未保存

INSTALLED_APPS = [
    ...
    'django.contrib.auth',
    'django.contrib.contenttypes',
    ...
]

from django.contrib.auth import authenticate, login

def login_view(request):
    if request.method == 'POST':
        username = request.POST['username']
        password = request.POST['password']
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            # 登录成功后的逻辑
        else:
            # 登录失败的逻辑
    else:
        # 显示登录页面的逻辑

MIDDLEWARE = [
    ...
    'django.contrib.sessions.middleware.SessionMiddleware',
    ...
]

from django.contrib.auth import authenticate, login

def login_view(request):
    if request.method == 'POST':
        username = request.POST['username']
        password = request.POST['password']
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            request.session['is_logged_in'] = True
            # 登录成功后的逻辑
        else:
            # 登录失败的逻辑
    else:
        # 显示登录页面的逻辑

def protected_view(request):
    if request.session.get('is_logged_in', False):
        # 用户已登录的逻辑
    else:
        # 用户未登录的逻辑