if request.user.is_authenticated(): # 判断是否登录
  return redirect('/index/')
else：
  return redirect('/accounts/login/')

from django.shortcuts import redirect
from django.views.decorators.cache import never_cache
from django.views.decorators.csrf import csrf_exempt
from django.contrib.auth import login as auth_login, authenticate
from app01.models import UCenter # 用户信息表


@csrf_exempt
@never_cache
def login(request):
  if request.user.is_authenticated():
    return redirect('/index/')
  else:
    if request.method == "POST":
      username = request.POST.get("username")
      password = request.POST.get("password")
      authenticated_user = authenticate(username=username, password=password)
      if authenticated_user:
        
        # 单用户登录
        user_obj = UCenter.objects.filter(userid=authenticated_user) # 找到登录的user对象
        is_session_key = user_obj.first().session_key # 获取登录对象的session_key
        if is_session_key: # 用户已登录
          request.session.delete(is_session_key) # 删除登录前面登录用户的session_key
        auth_login(request, authenticated_user) # 用户信息存入session
        user_obj.update(session_key=request.session.session_key) # 更新新登录user的session_key
        return redirect('/index/')
      else:
        return redirect('/accounts/login/')