好吧，尝试了几种不同的方法之后，我明白了。
这是我的工作方式：

Ok, After trying a few different things I got it. Here's how I made it work:

首先创建一个中间件，以便在用户最后一次访问服务器时将其存储在内存缓存中。

First create a Middleware to store on memcache the last time the user has accessed the server.

import datetime
from django.core.cache import cache
from django.conf import settings
from django.utils.deprecation import MiddlewareMixin


class ActiveUserMiddleware(MiddlewareMixin):

    def process_request(self, request):
        current_user = request.user
        if request.user.is_authenticated():
            now = datetime.datetime.now()
            cache.set('seen_%s' % (current_user.username), now,
                           settings.USER_LASTSEEN_TIMEOUT)

然后使用 online $属性扩展用户序列化程序c $ c>和 last_seen

class UserSerializer(serializers.ModelSerializer):

    last_seen = serializers.SerializerMethodField()
    online = serializers.SerializerMethodField()

    class Meta:
        model = User
        fields = ('url', 'id', 'username', 'email', 'first_name', 'last_name', 'groups', 'is_staff', 'avatar', 'last_seen', 'online')

    def get_last_seen(self, obj):
        last_seen = cache.get('seen_%s' % obj.username)
        obj.last_seen = last_seen
        return last_seen

    def get_online(self, obj):
        if obj.last_seen:
            now = datetime.datetime.now()
            delta = datetime.timedelta(seconds=settings.USER_ONLINE_TIMEOUT)
            if now > obj.last_seen + delta:
                return False
            else:
                return True
        else:
            return False

Settings.py需要具有以下新设置：

Settings.py need to have this new settings:

if os.name == 'nt':
    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache',
            'LOCATION': 'c:/foo/bar',
        }
    }
else:
    CACHES = {
            'default': {
                'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
                'LOCATION': '127.0.0.1:11211',
            }
    }


# Number of seconds of inactivity before a user is marked offline
USER_ONLINE_TIMEOUT = 300

# Number of seconds that we will keep track of inactive users before
# their last seen is removed from the cache
USER_LASTSEEN_TIMEOUT = 60 * 60 * 24 * 7

并且不要忘记添加中间件：

and do not forget to add your middleware:

'api.resources.users.middleware.active_user.ActiveUserMiddleware',