The Rails Drop

$ rake about

About your application's environment
Ruby version 1.9.2 (i686-linux)
RubyGems version 1.8.10
Rack version 1.3
Rails version 3.1.3
JavaScript Runtime therubyracer (V8)
Active Record version 3.1.3
Action Pack version 3.1.3
Active Resource version 3.1.3
Action Mailer version 3.1.3
Active Support version 3.1.3
Middleware Rack::Cache, ActionDispatch::Static, Rack::Lock, Rack::Runtime, Rack::MethodOverride, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::RemoteIp, Rack::Sendfile, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ParamsParser, ActionDispatch::Head, Rack::ConditionalGet, Rack::ETag, ActionDispatch::BestStandardsSupport, Warden::Manager, OmniAuth::Builder
Application root /home/abhi/my_app
Environment development
Database adapter mysql2
Database schema version 20120704103548

Rails Console ‘sandbox’ to test your rails application data

We know that how useful the rails console is. We can access the database and manupulate the data, but if you wish to test out some code without changing any data of your database, you can use sandbox option rails console –sandbox.

$ rails console --sandbox
Loading development environment in sandbox (Rails 3.1.0)
Any modifications you make will be rolled back on exit
irb(main):001:0>

How is it?

Shell command for killing all the processes together, that we found using grep command

Sometime when we found a lot of process associates with a software or something that may hurt our memory or CPU, and it would be nice to kill that all process and be our system in a fine position. But when there is so many process we can’t kill all the process by hand using the command

 $ kill -9 PID

where ‘PID’ is the process id.

Shell commands will help us to do this. See below

First you create a .sh file file named ‘killAllProcess.sh’.

#!/bin/bash
echo "Usage : ./killAllProcess.sh "
for i in `ps ax | grep $1 | grep -v grep | sed 's/ *//' | sed 's/[^0-9].*//'`
do
  kill -9 $i
done
echo "Killed All the process which has name with $1"

And make this file executable

$ chmod +x killAllProcess.sh

Then run it

 $ ./killAllProcess.sh

And see any process with that name is there

$ ps aux | grep PROCESS_NAME

All vanishes..!!

Ruby replace special characters with space

When I am seeking for this for Rails paperclip gem’s filename replacement, I found a very useful regular expression,

ruby-1.9.2-p290 :042 > name = "Abhi@## lash@###)(*&(!@"

=> "Abhi@## lash@###)(*&(!@"

ruby-1.9.2-p290 :043 > name.gsub(/([_@#!%()\-=;><,{}\~\[\]\.\/\?\"\*\^\$\+\-]+)/, ' ')

=> "Abhi lash & "

Ruby string method ‘scan’

Here I am writing about the ruby scan method for string.

syntax: scan(pattern) => array

Take a string name, where

irb> name = "Viswanathan Anand"

You scan through the string for words by,

ruby-1.9.2-p290 :014 > name.scan(/\w+/)
 => ["Viswanathan", "Anand"]

scan for 3 letters and make them an array element,

ruby-1.9.2-p290 :015 > name.scan(/.../)
 => ["Vis", "wan", "ath", "an ", "Ana"]

scan for 3 letters and group them with an array and make them array element,

ruby-1.9.2-p290 :016 > name.scan(/(...)/)
 => [["Vis"], ["wan"], ["ath"], ["an "], ["Ana"]]

and you can make three two pair letters in an array like:

ruby-1.9.2-p290 :017 > name.scan(/(...)(...)/)
 => [["Vis", "wan"], ["ath", "an "]]

You can also use reg exp like,

ruby-1.9.2-p290 :018 > name.scan(/[A-Z][a-z]+/)
 => ["Viswanathan", "Anand"]

Ruby Make Hash from two arrays

Suppose you want a hash with keys from an array and values from another array, use something like

ruby> ids = [1,2,3,4]
 => [1, 2, 3, 4]
ruby> names = ['Dan Brown', 'Stella', 'Parker']
=> ["Dan Brown", "Stella", "Parker"]

ruby> Hash[ids.zip names]
=> {1=>"Dan Brown", 2=>"Stella", 3=>"Parker", 4=>nil}

Rails MemCacheStore and dalli gem

We can use a memcached server for centralized caching in our application. This server is handling all caching mechanisms. Rails is using the gem memcache-client by default. But here I am using the dalli gem. Because it is better than memcache-client, but one thing to say is I am not experienced this. By reading documents, I have concluded that. You just go through this dalli gem link, https://github.com/mperham/dalli. This is a super caching mechanism by Rails in production environments. The Only thing we need to do is

Say you want caching in your application, by adding the following in your environments, add the following in your production.rb file, if you are running in production mode and you are using production.rb file as your environment configuration file.

config.action_controller.perform_caching = true

Just install dalli gem

Add the following in your gem file and do bundle install

$ gem 'dalli', '2.0.2'
$ bundle install

Install memcached server

$ sudo apt-get install memcached

Start the memcached server if not started

$ sudo /etc/init.d/memcached start

Configure in your environments, add the following in your production.rb file

config.cache_store = :dalli_store, 'YOUR_PRODUCTION_PUBLIC_DNS:11211',
    { :namespace => "app-YOUR_HOST", :expires_in => 1.day, :compress => true }

Here ‘YOUR_PRODUCTION_PUBLIC_DNS:11211’ is saying where your memcached server is running. Public DNS and the port number of the memcached server.

Take the rails console and experiment something like the following to know the MemCacheStore cache mechanism is working. If you are in localhost then do

ruby-1.9.2-p290 :003 > cache = Dalli::Client.new('localhost:11211')
 => #0}, @ring=nil> 
ruby-1.9.2-p290 :004 > cache.set('testing', 1234)
 => true
ruby-1.9.2-p290 :006 > cache.get('testing')
 => 1234

Now you are ready to go