Day: March 8, 2015

An Example for the difference between class and instance variable in Ruby

Create a ruby class called Test

class Test
   def cv=(value)
     @@cv = value
     end
   def cb=(value)
     @cb = value
     end
   def cv
     @@cv
     end
   def cb
     @cb
     end
   end
 => nil

Then create an instance of this class a and b

Try accessing the class variable without initializing it.

a = Test.new
 => # 
 a.cv
NameError: uninitialized class variable @@cv in Test
    from (irb):9:in `cv'
    from (irb):16

Initialize the class variable with some data. And add values to the instance variable of a and b.

a.cv=45
 => 45 

a.cv
 => 45 

b = Test.new
 => # 
b.cv
 => 45 
a.cb = 34
 => 34 
a.cb
 => 34 
b.cb
 => nil 
b.cb = 90
 => 90 
b.cb
 => 90

Rails way of creating a new full url with new parameters after removing old parameters from a url

If we have some keys and values and we just need to create a url with this data just pass the url and hash as a parameter to the following method.

def generate_url_with_params(url, params = {})
    uri = URI(url)
    uri.query = params.to_query
    uri.to_s
end

If you want to get rid of the parameters from a url use the following method.

  def generate_url_without_params(url, params = {})
    uri = URI(url)
    full_params = Rack::Utils.parse_query uri.query
    params.each do |key, val|
      full_params.delete key
    end
    uri.query = full_params.to_param
    uri.to_s
  end

How to implement a simple captcha in Rails using gem ‘simple_captcha’

Here it is, a simple captcha for Rails applications.

To set up, add the following line to your Gemfile

gem "galetahub-simple_captcha", :require => "simple_captcha"

Run rails generator

rails generate simple_captcha

Do db Migration

rake db:migrate -t

In your view file add

%= show_simple_captcha %

Add the following in yml file
en.yml:

en:
  simple_captcha:
    label: "Enter the above code"
    placeholder: "Enter here"

In controller just include captcha helpers module

class ApplicationController < ActionController::Base
  include SimpleCaptcha::ControllerHelpers
end

Use this code in the controller for the captcha validation

if simple_captcha_valid?
  do this
else
  do that
end