Recently I wanted a simple solution to track whether a user is online on a given Django site. The definition of "online" on a site is kind of ambiguous, so I'll define that a user is considered to be online if they have made any request to the site in the last five minutes.
I found that one approach is to use Django's caching framework to track when a user last accessed the site. For example, upon each request, I can have a middleware set the current time as a cache value associated with a given user. This allows us to store some basic information about logged-in user's online state without having to hit the database on each request and easily retrieve it by accessing the cache.
My approach below. Comments welcome.
In settings.py:
# add the middleware that you are about to create to settings
MIDDLEWARE_CLASSES = (
....
'middleware.activeuser_middleware.ActiveUserMiddleware',
....
)
# Setup caching per Django docs. In actuality, you'd probably use memcached instead of local memory.
CACHES = {
'default': {
'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
'LOCATION': 'default-cache'
}
}
# 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 for before
# their last seen is removed from the cache
USER_LASTSEEN_TIMEOUT = 60 * 60 * 24 * 7
In activeuser_middleware.py:
import datetime
from django.core.cache import cache
from django.conf import settings
class ActiveUserMiddleware:
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)
In your UserProfile module or some other model associated with the user:
class UserProfile(models.Model):
....
....
def last_seen(self):
return cache.get('seen_%s' % self.user.username)
def online(self):
if self.last_seen():
now = datetime.datetime.now()
if now > self.last_seen() + datetime.timedelta(
seconds=settings.USER_ONLINE_TIMEOUT):
return False
else:
return True
else:
return False
Then in the template where you want to display whether the user is online or not:
{% with request.user.get_profile as profile %}
<table>
<tr><th>Last Seen</th><td>{% if profile.last_seen %}{{ profile.last_seen|timesince }}{% else %}awhile{% endif %} ago</td></tr>
<tr><th>Online</th><td>{{ profile.online }}</td></tr>
</table>
{% endwith %}
Pros:
- Simple solution
- Doesn't need to hit the database for saving the timestamp each request
Cons:
- Last user access times are cleared if the server is rebooted or cache is reset
- Last user access times are accessible only as long as they exist in the cache.
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