sravani – @Cybrilla

Many of us used of so many gems in ruby, so lets try to create a basic gem.
Simple, We just have to generate two files to create your own gem.

Step1: Create a gemspec.
Create a gemspec file inside root directory, file-name should be same as your gem name (Eg: In our case its greeting_gem.gemspec)

– Specify your gem specifications

Gem::Specification.new do |s|
   s.name = "greeting_gem"
   s.version = '0.0.0'
   s.date = '2013-11-28'
   s.summary = "Greeting Gem"
   s.description = "A simple greeting gem"
   s.authors = "Sravani Perala"
   s.files = "lib/greeting_gem.rb"
end

Gem::Specification.new do |s|

s.name = "greeting_gem"

s.version = '0.0.0'

s.date = '2013-11-28'

s.summary = "Greeting Gem"

s.description = "A simple greeting gem"

s.authors = "Sravani Perala"

s.files = "lib/greeting_gem.rb"

end

Step2: Add some code.
Create a greeting_gem.rb file in lib folder

class GreetingGem
  def self.greeting(name)
    puts "Helloo #{name}"
  end
end

class GreetingGem

def self.greeting(name)

puts "Helloo #{name}"

end

Step 3: Generate gem file.

 gem build greeting_gem.gemspec

1	gem build greeting_gem.gemspec

This command will build the gem, which can be used in another ruby program.

Step 4: Test the gem.
gem install greeting_gem, to install the gem locally to test it out.
open irb
>> require ‘greeting_gem’
=> true
>> GreetingGem.greeting(‘sravani’)
Hello sravani

Isn’t it simple!
Add as many methods you want in the same way and move on to bigger things.

I realized the importance of reading documentation clearly and with care, when I spent hours debugging this stupid problem.

This is an Active Record callback in action. We are setting a boolean field ‘approved’ to false in the before_create ActiveRecord callback.

class Topic  &lt; ActiveRecord::Base
  before_create :send_to_admin_approval

  private
  def send_to_admin_approval
    self.approved = false
  end
end

class Topic < ActiveRecord::Base

before_create :send_to_admin_approval

private

def send_to_admin_approval

self.approved = false

end

This code is simple, straightforward and looks flawless, until you see a ActiveRecord::RecordNotSaved exception when you try to create a Topic. Our only savior, the errors object also doesn’t give us any information on what went wrong.

Two important things we always forget and aren’t quite obvious are

1. Implicit return values in Ruby. This feature always returns the value of the last executed statement in a method or block.

2. If an ActiveRecord callback returns false, all the later callbacks and the associated action are cancelled.

In our example, the statement ‘self.approved = false’ returns false and since that is the last statement executed in the callback, the callback returns false which cancels the create operation.

So, the best way to set boolean values in an ActiveRecord callback is

class Topic &lt; ActiveRecord::Base
  before_create :send_to_admin_approval

  def send_to_admin_approval
    self.approved = false
    true # Explicitly return true
  end
end

class Topic < ActiveRecord::Base

before_create :send_to_admin_approval

def send_to_admin_approval

self.approved = false

true # Explicitly return true

end

@Cybrilla

Ordinary people, Extraordinary dreams

Author Archives: sravani

Creating Your First Gem is Easy…

RailsTip: Setting boolean values in ActiveRecord callbacks