Skip to main content

Posts

Showing posts from July, 2011

Django: Using Caching to Track Online Users

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...

Django Permission TemplateTag

In a previous post , I wrote about a way to keep track of user permissions on a model instance.  For example, I suggested that each model have a permissions subclass that could be instantiated with a user instance passed as a constructor argument.  Methods on that permissions class could then be called to determine if that user has permission to perform various actions. I also suggested that the threadlocals module could then be used to pass in the user instance to the permissions object in the Django template.  However, from various readings, I get the impression that threadlocals may not be the best thing for passing arguments in a template function.   Therefore, I decided to use a more traditional route of creating a template tag to do something similar. I created a template tag that lets you surround a block of HTML code to hide or show the contents based on the return value of the permission function.  The tag below basically says, "if the logged in use...