Michael Bensoussan

Register to an image loaded event with jQuery

2010-07-26T01:29:00+02:00

I was recently working on a lightbox where I needed to display a remote image and re-center the lighbox once the image is loaded. This may seems pretty simple but it took me some time to discover that jQuery does the job via the load method. As soon as the image has been loaded, the handler is called.

Creating an activity feed with rails

2010-05-23T01:12:00+02:00

I recently had to build an activity feed at letitcast.com. It’s a common thing to do, but I thought I might mention how I did it, and see if anyone else has suggestions/improvements.

We wanted to display to our actors new roles corresponding their profile, new feedbacks and views of their auditions, recent comments …

So, I first created a model Activity, here’s the migration :

class CreateActivities < ActiveRecord::Migration def self.up create_table :activities do |t| t.integer :user_id, :null => false t.integer :activity_type, :null => false t.integer :target_id, :null => false t.string :target_type, :null => false t.timestamps end add_index :activities, [:target_id, :target_type] add_index :activities, :user_id end def self.down drop_table :activities end end

As you can see it’s a polymorphic model, so the activity can be related to any active record model.

Here’s the model :

class Activity < ActiveRecord::Base belongs_to :user belongs_to :target, :polymorphic => true default_scope :order => 'activities.created_at DESC', :limit => 10 AUDITION_POSTED = 1 #target --> model audition AUDITION_FEEDBACK_UPDATED = 2 #target --> model audition AUDITION_VIEWED = 3 #target --> model video NEW_PART = 4 #target --> model part class << self def add(user, activity_type, target) return false if user.blank? or activity_type.blank? or target.blank? activity = Activity.new(:user => user, :activity_type => activity_type, :target => target) activity.save! end end end

At the beginning the activity types were mapped in an other database but it was a bit overkill and was reducing the performance a lot so I just added them into the model (AUDITION_POSTED, AUDITION_FEEDBACK_UPDATED, …)

Activities are created with observers. In this exemple a new audition triggers an AUDITION_POSTED activity created.

class AuditionObserver < ActiveRecord::Observer # ACTIVITY OBSERVER : new audition posted def after_create(audition) if audition.actor Activity.add(audition.actor.user, Activity::AUDITION_POSTED, audition) end end end

Sooooo … I can add any event via a simple variable in the activity model and an observer.

It was working really well but there were some performance issues with some events that required a lot of inserts in the activity model. I first decided to execute this observer in a delayed job but after some research I ended up with a fast way to insert a batch of activities, here’s the method :

def self.batch_add(users, activity_type, target) return false if users.blank? or activity_type.blank? or target.blank? inserts = [] users.each {|user| inserts.push "('#{user.id}', '#{activity_type}', '#{target.id}', '#{target.class}', UTC_TIMESTAMP())" } sql = "INSERT INTO activities (`user_id`, `activity_type`, `target_id`, `target_type`, `created_at`) VALUES #{inserts.join(", ")}" ActiveRecord::Base.connection.execute sql end

To retrieve the activities :

By default you’ll get 10 activities order by most recents. If you want to change this behavior, just change the default_scope.

We’re also in the process of grouping the user activities to display them in a nice view, so there will maybe be a part II :-)

Optional local in partial that doesn't break

2010-05-22T00:58:00+02:00

If you have a partial called with or without local parameters, example :

And you don’t want the partial to break when the local isn’t assigned, you can access it through the local_assigns variable :

Using Nginx as a load balancer

2009-12-30T04:13:00+01:00

Here’s a look at how nginx does basic load balancing :

upstream yoursite { server yoursite1.yoursite.com; server yoursite2.yoursite.com; } server { server_name www.yoursite.com; location / { proxy_pass http://yoursite; } }

This configuration will send 50% of the requests for www.yoursite.com to yoursite1.yoursite.com and the other 50% to yoursite2.yoursite.com.

ip_hash

You can specify the ip_hash directive that guarantees the client request will always be transferred to the same server. If this server is considered inoperative, then the request of this client will be transferred to another server.

down

If one of the servers must be removed for some time, you must mark that server as down.

weight

If you add a weight tag onto the end of the server definition you can modify the percentages of the requests send to the servers. When there’s no weight set, the weight is equal to one.

This configuration will send 80% of the requests to yoursite1.yoursite.com and the other 20% to yoursite2.yoursite.com.

note: It’s not possible to combine ip_hash and weight directives.

max_fails and fail_timeout

max_fails is a directive defining the number of unsuccessful attempts in the time period defined by fail_timeout before the server is considered inoperative. If not set, the number of attempts is one. A value of 0 turns off this check. If fail_timeout is not set the time is 10 seconds.

In this configuration nginx will consider yoursite2.yoursite.com as inoperative if a request fails 3 times with a 30s timeout.

backup

If the non-backup servers are all down or busy, the server(s) with the backup directive will be used.

This configuration will send 50% of the requests for www.yoursite.com to yoursite1.yoursite.com and the other 50% to yoursite2.yoursite.com. If yoursite1.yoursite.com and yoursite2.yoursite.com both fails 3 times the requests will be send to yoursite3.yoursite.com.