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Plugins, Generators and
Gems
or
What do we need those for?

Who am I

Allan Davis
@cajun_code * cajun.code@gmail.com
https://github.com/cajun-code

Agenda
Generators

Plug-ins

Gems

What is a generator?
Generator is a rails command line process to
generate something inside the application

Any commands run under rails generate is a
generator.

You can view the list of available generators
by typing rails g

$ rails g

Usage: rails generate GENERATOR [args] [options]
General options:
-h, [--help] # Print generator's options and usage
-p, [--pretend] # Run but do not make any changes
-f, [--force] # Overwrite files that already exist
-s, [--skip] # Skip files that already exist
-q, [--quiet] # Suppress status output
Please choose a generator below.

Rails:
controller
generator
helper
integration_test
mailer
migration
model
observer
performance_test
plugin
resource
scaffold
scaffold_controller
session_migration
stylesheets

$ rails g generator

Usage:
rails generate generator NAME [options]
Options:
[--namespace] # Namespace generator under lib/generators/name
# Default: true
Runtime options:
-q, [--quiet] # Supress status output
Description:
Stubs out a new generator at lib/generators. Pass the generator name as an argu
either CamelCased or snake_cased.

Example:
`rails generate generator Awesome`

creates a standard awesome generator:
lib/generators/awesome/
lib/generators/awesome/awesome_generator.rb
lib/generators/awesome/USAGE
lib/generators/awesome/templates/

$ rails g generator install
create lib/generators/install
create lib/generators/install/install_generator.rb
create lib/generators/install/USAGE
create lib/generators/install/templates

Created Two Files and a Folder
_generator.rb - Worker file

USAGE - text document describing the generator

templates - directory for erb templates used in the
generator

Lets Look at the generator

class InstallGenerator < Rails::Generators::NamedBase
source_root File.expand_path('../templates', __FILE__)
end

The USAGE file.
$ cat USAGE

Description:
Explain the generator
Example:
rails generate install Thing
This will create:
what/will/it/create

Download the 960 stylesheets
https://raw.github.com/nathansmith/960-Grid-System/master/code/css/

$ cd lib/generators/install/templates
$ wget https://.../960.css
$ wget https://.../reset.css
$ wget https://.../text.css

Lets edit the install_generator.rb to cop
module Grid960
class InstallGenerator < Rails::Generators::Base
source_root File.expand_path('../templates', __FILE__)
def remove_old_layout
remove_file "app/views/layouts/application.html.erb"
end

def copy_stylesheets
copy_file "960.css", "public/stylesheets/960.css"
copy_file "reset.css", "public/stylesheets/reset.css"
copy_file "text.css", "public/stylesheets/text.css"
template "layout.html.erb", "app/views/layouts/application.html.er
end
def app_name
Rails.application.class.name.split("::")[0]
end
end
end

layout.html.erb
Create in the templates directory

<!DOCTYPE html>
<html>
<head>
<title><%= app_name %></title>
<%%= stylesheet_link_tag "reset" %>
<%%= stylesheet_link_tag "text" %>
<%%= stylesheet_link_tag "960" %>
<%%= stylesheet_link_tag "scaffold" %>
<%%= javascript_include_tag :defaults %>
<%%= csrf_meta_tag %>
</head>
<body>

<%= yield %>

</body>
</html>

Execute the generator
$ rails g grid960:install

What are Plugins
Encapsulated functionality meant to extend
rails

Plugins are installed into a rails application

$ rails plugin

Usage: plugin [OPTIONS] command
Rails plugin manager.
GENERAL OPTIONS
-r, --root=DIR Set an explicit rails app directory.
Default: /home/alley/Projects/emerald_generators/code/contacts
-s, --source=URL1,URL2 Use the specified plugin repositories instead of the defaults.
-v, --verbose Turn on verbose output.
-h, --help Show this help message.

COMMANDS
install Install plugin(s) from known repositories or URLs.
remove Uninstall plugins.
EXAMPLES
Install a plugin:
rails plugin install continuous_builder
Install a plugin from a subversion URL:
rails plugin install http://dev.rubyonrails.com/svn/rails/plugins/continuous_builder
Install a plugin from a git URL:
rails plugin install git://github.com/SomeGuy/my_awesome_plugin.git

$ rails g plugin

Usage:
rails generate plugin NAME [options]

Options:
-r, [--tasks=TASKS] # When supplied creates tasks base files.
-g, [--generator] # Indicates when to generate generator
-t, [--test-framework=NAME] # Test framework to be invoked
# Default: test_unit

Runtime options:
-q, [--quiet] # Supress status output
Description:
Stubs out a new plugin at vendor/plugins. Pass the plugin name, either
CamelCased or under_scored, as an argument.
Example:
`rails generate plugin BrowserFilters`
creates a standard browser_filters plugin:
vendor/plugins/browser_filters/README
vendor/plugins/browser_filters/init.rb
vendor/plugins/browser_filters/install.rb
vendor/plugins/browser_filters/lib/browser_filters.rb
vendor/plugins/browser_filters/test/browser_filters_test.rb

Create grid960 plugin
$ rails g plugin grid960

create vendor/plugins/grid960
create vendor/plugins/grid960/MIT-LICENSE
create vendor/plugins/grid960/README
create vendor/plugins/grid960/Rakefile
create vendor/plugins/grid960/init.rb
create vendor/plugins/grid960/install.rb
create vendor/plugins/grid960/uninstall.rb
create vendor/plugins/grid960/lib
create vendor/plugins/grid960/lib/grid960.rb
invoke test_unit
inside vendor/plugins/grid960
create test
create test/grid960_test.rb
create test/test_helper.rb

Copy the generator
from lib to plugin

$cp -R lib/generators vendor/plugins/grid960/lib

Rails G
to check if generator loaded

$rails g

Grid960
grid960:install

What are Gems
System use to distribute external libraries.

Zip compressed file for libraries storage

Using Bundler to Create Gems
$ bundle gem grid960
create grid960/Gemfile
create grid960/Rakefile
create grid960/.gitignore
create grid960/grid960.gemspec
create grid960/lib/grid960.rb
create grid960/lib/grid960/version.rb
Initializating git repo in /home/alley/Projects/emerald_generators/code/grid960

gemspec File
# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "grid960/version"

Gem::Specification.new do |s|
s.name = "grid960"
s.version = Grid960::VERSION
s.platform = Gem::Platform::RUBY
s.authors = ["TODO: Write your name"]
s.email = ["TODO: Write your email address"]
s.homepage = ""
s.summary = %q{TODO: Write a gem summary}
s.description = %q{TODO: Write a gem description}

s.rubyforge_project = "grid960"
s.add_dependency "rails", ">3.0.0"
s.files = `git ls-files`.split("n")
s.test_files = `git ls-files -- {test,spec,features}/*`.split
s.executables = `git ls-files -- bin/*`.split("n").map{ |f| File
s.require_paths = ["lib"]
end

Copy generator code inside
lib directory

Develop the gem
Create a test project with rails new

Add the grid960 gem to the Gemfile

Use the :path => to point to the gem on the file system

Run Rails g command to use the generator

Package and Deploy
To package the gem run rake build

To deploy the gem run "gem push
pkg/grid960-0.0.1.gem"

Resources
http://railscasts.com/episodes/218-making-
generators-in-rails-3

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