So what do mixin modules do?  Basically they allow you to code instance methods into a module and then include the module in a class.  The class will then have access to the instance methods in a module.  Pretty nice when you have shared functionality between models.  You can code one module and include it in several models.

Here is an example:

module LoudModule
  def explode
    "BOOM!"
  end
end

class BottleRocket
  include LoudModule
end

class FireCracker
  include LoudModule
end

firecracker = FireCracker.new
p firecracker.explode

bottlerocket = BottleRocket.new
p bottlerocket.explode

As you can see firecracker and bottlerocket both have access to the “explode” instance method in the module.

Now to make this work with a Rails plugin where you need a model base class:

module BaseWidget
  self.included?(base)
    base.belongs_to :manufacturer
  end

  def some_instance_method
    "test"
  end
end

class Widget < ActiveRecord::Base
  unloadable
  use_db :prefix => "mydatabse_prefix_"
  include BaseWidget
  def some_new_instance_method
    "test2"
  end
end

This is pretty cool because it will allow you to define a base class for your model that you can reuse in different applications. The self.included? block allows you to load use the instance methods from the base class (ActiveRecord::Base in this case). So Widget will have access to all the associations, named_scopes and act_as* methods from the Base class.

Server setup shell script:  setup.sh

This worked for me last time I tried it. YMMV

I am installing this on a clean, stripped-down version of CentOS on Rackspace cloud.  So first things first, you need to install a c compiler and make

>yum install gcc

>yum install make

Next you need to install libevent

> wget http://www.monkey.org/~provos/libevent-1.4.13-stable.tar.gz

> tar -xvf libevent-1.4.13-stable.tar.gz

> cd libevent-1.4.13-stable

>./configure && make

> make install

Good to go.. now you will need to download and install memcached

> cd ..

> wget http://memcached.googlecode.com/files/memcached-1.4.4.tar.gz
> tar -xvf memcached-1.4.4.tar.gz
> cd memcached-1.4.4
> ./configure && make
> make install

Now you can start memcached

> /usr/local/bin/memcached -u nobody &

I also add this command (without the ‘&’ at the end) to /etc/rc.local, so memcached starts automatically if the server is rebooted

When you start memcached you may get the following error:

/usr/local/bin/memcached: error while loading shared libraries: libevent-1.4.so.2: cannot open shared object file: No such file or directory

Here is the fix:

Create this file

> nano /etc/ld.so.conf.d/libevent-i386.conf

add the following line to the file and close and save it:

/usr/local/lib/

then run this command

> /sbin/ldconfig

You should be able to start memcached now without the error

>/usr/local/bin/memcached -u nobody &

You can get the status like this if you have ‘nc’ installed (yum install nc, if not)

> echo stats | nc 127.0.0.1 11211

Memcached is now installed and working correctly.  Do the following to configure your rails app to work with it.  On the server that contains your Rails code:

> gem install memcache-client

Uncomment or add this line to /your-rails-app/config/environments/production.rb

config.cache_store = :mem_cache_store

Add caching code to your rails app.  For example you could cache an action in the ProductsController like this:

class ProductsController < ApplicationController
   caches_action :some_action, :expires_in => 1.hour
   ...
end

restart your rails app and you should be good to go

named_scope :filter_non_secondary_website_data, :conditions=>”secondary_website=1″

I know you can chain named_scopes to each other, but I was wondering if I could chain it to a find method also.  At first I appending it to the end of a find like this

records = SomeModel.find(:all,:conditions=>” you=’awesome’ “).filter_non_secondary_website_data

Nope that didnt work.  If I remember the error was something about that method not existing for type array.  In order to make this work you need to append it to the beginning so the find can combine it with its SQL.  Here is the correct way which will append the SQL “AND secondary_website=1″ to the find’s SQL

records = SomeModel.filter_non_secondary_website_data.find(:all,:conditions=>” you=’awesome’ “)

That works.  There is probably a way I could override the find method in the model and add this code.  Anybody know??  I just searched my project for all finds and added the method.  Not exactly an optimal solution if you have a hundred finds.. but anyways, pretty cool that you can chain a named scope to find if you need to.

<div style="margin: 0pt; padding: 0pt; float: left; width: 150px;">
  <img style="margin: 0pt; padding: 0pt; width: 150px; float: left;display:block;" src="some-image.gif" alt="" />
  <img style="margin: 0pt; padding: 0pt; width: 150px; float: left;display:block;" src="some-image.gif" alt="" />
</div>

>mysql -u root -pyourpassword -e “create database some_database_name;”

NOTE: when I pasted this into bash, I had to change the quotes.. I guess wordpress converts them to a different encoding

>SHOW SLAVE STATUS \G;

This showed me the error, so I went back and deleted the column on the slave so the alter statement on the slave would finish without error.  Then all you have to do is stop slave and then start slave

>STOP SLAVE;

>START SLAVE;

The slave should catch up to the master shortly.  NOTE TO SELF… make slave user read only.

>sudo passwd root

Enter your user account password and then enter the new root password twice.  After that issue the “su” command and enter the password you just created.  You have super user access now.

class Widget < ActiveRecord::Base
  named_scope :blues, :conditions=> "color='blue'"
end

Thats pretty cool huh? Very DRY if you are going to be using this quite a bit. Here is a more complex example where you can insert a parameter using lambda.

  named_scope :above_price, lambda { |*args| {:conditions => ["price>?",args.first] } }

  #get all widgets with price above $25
  Widget.above_price(25)

Even cooler…
Now here is something I like even better that I was not expecting, but it seems to work. I am able to chain these together to filter out different widgets based on criteria. This is useful in an application that needs to allow users to filter out certain content based on criteria. Lets say you have a list full of widgets of all kinds, but the user only wants to see widgets that are blue and cost more than $25. You can add some check boxes and inputs to your view with a submit button and let the user choose different criteria so they can find the widget they are looking for. Then you can filter out the widgets with named scopes in your controller

widgets = Widget.all
if params[:is_blue]
  widgets = widgets.blues
end
if params[:above_price]
  widgets = widgets.above_price(params[:above_price])
end
#now you would have all the blue widgets above whatever price the user entered in the field "above_price"

#If I remember correctly, you can also call them by chaining them together if you need to
widgets = widgets.blue.above_price(25)

I think this is a pretty elegant solution for doing object filtering in Rails. Go named_scope! You crazy!

First thing you want to do when creating a facebook app is to log on to Facebook Developer -> http://www.facebook.com/developers/. They have 2 sites for this and dont ask me why. The other one is developer.facebook.com. Do not use that one, because there is no way to edit your app from that page.

From http://www.facebook.com/developers/, click “Set up New Application” and enter an app name. After that you will go to the “Edit” screen for your application. There are a ton of different things you can configure, like the icon, etc.., but for now you just need to worry about your canvas settings. Click “Canvas” in the left side menu. Enter a name for your app: http://apps.facebook.com/your-app-name-goes-here . Next is the most important part, the “Canvas Callback URL”. For this, you need to enter the URL of your application. Since this is going to be an iFrame application, your app will be retrieved from your servers. So I entered: http://www.myapp.com/facebook/canvas. Next make sure you select “iFrame” under canvas render method. Save your changes and its time to start coding with Rails

Here is a screenshot of my settings:

You will need to install facebooker as a plugin. Follow the instructions on github – http://github.com/mmangino/facebooker

Rails Stuff
1. Create a controller called “facebook_controller.rb”
2. Add an action for your canvas page. This will be like the welcome page for your application
3. Add “ensure_authenticated_to_facebook” to the top of your controller. I will talk about this in more detail later.

4. Set up your view (canvas.html.erb) with whatever you want in it. “Hello world”

class FacebookController < ApplicationController
  ensure_authenticated_to_facebook

  def canvas
  end
end

Since you are the developer and you set up the app in facebook, it will already be installed in your facebook account. You can test it by going to http://apps.facebook.com/name-of-your-app-goes-here
You should see your app render in the iframe. Now lets move on to where the app actually does something. Create a link in your view to go to another action that will count your friends

canvas.html.erb

Now you need to add the action to your facebook_controller.rb:

def count_friends
  @count = 0
  #this session variable is set automatically by the facebooker plugin
  fbsession = session[:facebook_session]
  #iterate thru your friends.  fbsession.user grabs your user account and then .friends pulls in all your friends
  fbsession.user.friends.each do |user|
    @count += 1
  end
end

count_friends.html.erb

Woopty doo! You have a working facebook app using Ruby on Rails and Facebooker.

Now if you try to send this to your friends it will not work, because of some changes in the facebook api that were not changed in Facebooker. The main problem lies in the install_url. When your friend tries to install the facebook app, it will send them to your website (no iFrame, just your site outside facebook..no good), instead of directing them to your canvas page which contains your website in an iFrame. To fix this I just hardcoded :canvas=>”true” in this method:

starting at line #189 in vendor/plugins/facebooker/lib/facebooker/rails/controller.rb. I commented out one line and hard coded in a value for canvas. Not sure if this breaks anything else, but it seems fine so far. I am guessing facebook changed something with the fb_sig_in_cavas parameter.

      def create_new_facebook_session_and_redirect!
        session[:facebook_session] = new_facebook_session
        next_url = after_facebook_login_url || default_after_facebook_login_url
        #top_redirect_to session[:facebook_session].login_url({:next => next_url, :canvas=>params[:fb_sig_in_canvas]}) unless @installation_required
        top_redirect_to session[:facebook_session].login_url({:next => next_url, :canvas=>"true"}) unless @installation_required
        false
      end

Push this change to your server and restart your app and this should make everything show up in the iframe after the facebook user installs your app.

On a side note: if you try to use “ensure_application_is_installed_by_facebook_user” in your controller, instead of “ensure_authenticated_to_facebook”, you will get the opposite effect when you click on a link within your application. It will turn into an infinite iframe loop. Every time you click it will create another page inside the iFrame