matt-beedle.com

Well, this is my first post. I was frustrated in to starting this blog, through searching the internet for solutions to various programming problems, and finding either nothing, or only half the answer. Hopefully I will be able to help others solve some of their problems faster. Recently I have been writing a dating site in ruby on rails. One quite important feature of this site is a list of members who are currently online. After a couple of days of pain, here’s the pretty simple solution to the problem:

First off this only works if you use ActiveRecord to manage your sessions. To do this you must uncomment the following line in your environment.rb file:

config.action_controller.session_store = :active_record_store

Then create the sessions table by running the following command from your RAILS_ROOT:

rake db:sessions:create

Now, whenever a user logs in to your application add their id to the session. In my app at the moment it looks something like this:

member = Member.new( @params[ :member ] )
member = Member.find( :all, :conditions => "screen_name = '#{member.screen_name}' AND password = '#{member.password}'" )
if member != nil
  session[ :member_id ] = member.id
  redirect_to :action => 'success'
else
  redirect_to :action => 'form'
end

This code will need work for a production environment, for one thing it is open to SQL injection attacks.
Now to find all of the users who are currently online it is just a matter of searching the sessions table for all the users who have been active in the last 10 minutes. This can be done using rails built in session model. Finally the session data needs to be unmarshaled and decoded. This stumped me for a while, but finally I found the answer at http://caboo.se/doc/classes/CGI/Session/ActiveRecordStore/SqlBypass.html. So here is my code to return an array of the member_ids of all the members online and active within the last 10 minutes.

def who_is_online
  @whos_online = Array.new()
  onlines = CGI::Session::ActiveRecordStore::Session.find( :all, :conditions => [ 'updated_at = ?', Time.now() - 10.minutes ] )
  onlines.each do |online|
    id = Marshal.load( Base64.decode64( online.data ) )
    @whos_online << id[ :member_id ]
  end
  return @whos_online
end