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Added a tutorial for how to create and test plugins

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+Creating Plugin Basics
+====================
+
+Pretend for a moment that you are an avid bird watcher. Your favorite bird is the Yaffle, and you want to create a plugin that allows other developers to share in the Yaffle goodness.
+
+In this tutorial you will learn how to create a plugin that includes:
+
+Core Extensions - extending String:
+
+ # Anywhere
+ "hello".squawk # => "squawk! hello! squawk!"
+
+An acts\_as\_yaffle method for Active Record models that adds a "squawk" method:
+
+ class Hickwall < ActiveRecord::Base
+ acts_as_yaffle :yaffle_text_field => :last_sang_at
+ end
+
+ Hickwall.new.squawk("Hello World")
+
+A view helper that will print out squawking info:
+
+ squawk_info_for(@hickwall)
+
+A generator that creates a migration to add squawk columns to a model:
+
+ script/generate yaffle hickwall
+
+A custom generator command:
+
+ class YaffleGenerator < Rails::Generator::NamedBase
+ def manifest
+ m.yaffle_definition
+ end
+ end
+ end
+
+A custom route method:
+
+ ActionController::Routing::Routes.draw do |map|
+ map.yaffles
+ end
+
+In addition you'll learn how to:
+
+* test your plugins
+* work with init.rb, how to store model, views, controllers, helpers and even other plugins in your plugins
+* create documentation for your plugin.
+
+Create the basic app
+---------------------
+
+In this tutorial we will create a basic rails application with 1 resource: bird. Start out by building the basic rails app:
+
+> The following instructions will work for sqlite3. For more detailed instructions on how to create a rails app for other databases see the API docs.
+
+ rails plugin_demo
+ cd plugin_demo
+ script/generate scaffold bird name:string
+ rake db:migrate
+ script/server
+
+Then navigate to [http://localhost:3000/birds](http://localhost:3000/birds). Make sure you have a functioning rails app before continuing.
+
+Create the plugin
+-----------------------
+
+The built-in Rails plugin generator stubs out a new plugin. Pass the plugin name, either CamelCased or under_scored, as an argument. Pass --with-generator to add an example generator also.
+
+This creates a plugin in vendor/plugins including an init.rb and README as well as standard lib, task, and test directories.
+
+Examples:
+
+ ./script/generate plugin BrowserFilters
+ ./script/generate plugin BrowserFilters --with-generator
+
+Later in the plugin we will create a generator, so go ahead and add the --with-generator option now:
+
+ script/generate plugin yaffle --with-generator
+
+You should see the following output:
+
+ create vendor/plugins/yaffle/lib
+ create vendor/plugins/yaffle/tasks
+ create vendor/plugins/yaffle/test
+ create vendor/plugins/yaffle/README
+ create vendor/plugins/yaffle/MIT-LICENSE
+ create vendor/plugins/yaffle/Rakefile
+ create vendor/plugins/yaffle/init.rb
+ create vendor/plugins/yaffle/install.rb
+ create vendor/plugins/yaffle/uninstall.rb
+ create vendor/plugins/yaffle/lib/yaffle.rb
+ create vendor/plugins/yaffle/tasks/yaffle_tasks.rake
+ create vendor/plugins/yaffle/test/core_ext_test.rb
+ create vendor/plugins/yaffle/generators
+ create vendor/plugins/yaffle/generators/yaffle
+ create vendor/plugins/yaffle/generators/yaffle/templates
+ create vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
+ create vendor/plugins/yaffle/generators/yaffle/USAGE
+
+For this plugin you won't need the file vendor/plugins/yaffle/lib/yaffle.rb so you can delete that.
+
+ rm vendor/plugins/yaffle/lib/yaffle.rb
+
+> Editor's note: many plugin authors prefer to keep this file, and add all of the require statements in it. That way, they only line in init.rb would be `require "yaffle"`
+> If you are developing a plugin that has a lot of files in the lib directory, you may want to create a subdirectory like lib/yaffle and store your files in there. That way your init.rb file stays clean
+
+Testing Setup
+------------------------
+
+Testing plugins that use the entire Rails stack can be complex, and the generator doesn't offer any help. In this tutorial you will learn how to test your plugin against multiple different adapters using ActiveRecord. This tutorial will not cover how to use fixtures in plugin tests.
+
+To setup your plugin to allow for easy testing you'll need to add 3 files:
+
+* A database.yml file with all of your connection strings
+* A schema.rb file with your table definitions
+* A test helper that sets up the database before your tests
+
+For this plugin you'll need 2 tables/models, Hickwalls and Wickwalls, so add the following files:
+
+ # File: vendor/plugins/yaffle/test/database.yml
+
+ sqlite:
+ :adapter: sqlite
+ :dbfile: yaffle_plugin.sqlite.db
+ sqlite3:
+ :adapter: sqlite3
+ :dbfile: yaffle_plugin.sqlite3.db
+ postgresql:
+ :adapter: postgresql
+ :username: postgres
+ :password: postgres
+ :database: yaffle_plugin_test
+ :min_messages: ERROR
+ mysql:
+ :adapter: mysql
+ :host: localhost
+ :username: rails
+ :password:
+ :database: yaffle_plugin_test
+
+ # File: vendor/plugins/yaffle/test/test_helper.rb
+
+ ActiveRecord::Schema.define(:version => 0) do
+ create_table :hickwalls, :force => true do |t|
+ t.string :name
+ t.string :last_squawk
+ t.datetime :last_squawked_at
+ end
+ create_table :wickwalls, :force => true do |t|
+ t.string :name
+ t.string :last_tweet
+ t.datetime :last_tweeted_at
+ end
+ end
+
+ # File: vendor/plugins/yaffle/test/test_helper.rb
+
+ ENV['RAILS_ENV'] = 'test'
+ ENV['RAILS_ROOT'] ||= File.dirname(__FILE__) + '/../../../..'
+
+ require 'test/unit'
+ require File.expand_path(File.join(ENV['RAILS_ROOT'], 'config/environment.rb'))
+
+ config = YAML::load(IO.read(File.dirname(__FILE__) + '/database.yml'))
+ ActiveRecord::Base.logger = Logger.new(File.dirname(__FILE__) + "/debug.log")
+
+ db_adapter = ENV['DB']
+
+ # no db passed, try one of these fine config-free DBs before bombing.
+ db_adapter ||=
+ begin
+ require 'rubygems'
+ require 'sqlite'
+ 'sqlite'
+ rescue MissingSourceFile
+ begin
+ require 'sqlite3'
+ 'sqlite3'
+ rescue MissingSourceFile
+ end
+ end
+
+ if db_adapter.nil?
+ raise "No DB Adapter selected. Pass the DB= option to pick one, or install Sqlite or Sqlite3."
+ end
+
+ ActiveRecord::Base.establish_connection(config[db_adapter])
+
+ load(File.dirname(__FILE__) + "/schema.rb")
+
+ require File.dirname(__FILE__) + '/../init.rb'
+
+ class Hickwall < ActiveRecord::Base
+ acts_as_yaffle
+ end
+
+ class Wickwall < ActiveRecord::Base
+ acts_as_yaffle :yaffle_text_field => :last_tweet, :yaffle_date_field => :last_tweeted_at
+ end
+
+Update a core class: Adding "to\_squawk" to String
+-----------------------
+
+To update a core class you will have to:
+
+* Write tests for the desired functionality
+* Create a file for the code you wish to use
+* Require that file from your init.rb
+
+Most plugins store their code classes in the plugin's lib directory. When you add a file to the lib directory, you must also require that file from init.rb. The file you are going to add for this tutorial is `lib/core_ext.rb`
+
+First, you need to write the tests. Testing plugins is very similar to testing rails apps. The generated test file should look something like this:
+
+ # File: vendor/plugins/yaffle/test/core_ext_test.rb
+
+ require 'test/unit'
+
+ class CoreExtTest < Test::Unit::TestCase
+ # Replace this with your real tests.
+ def test_this_plugin
+ flunk
+ end
+ end
+
+Start off by removing the default test, and adding a require statement for your test helper.
+
+ # File: vendor/plugins/yaffle/test/core_ext_test.rb
+
+ require 'test/unit'
+ require File.dirname(__FILE__) + '/test_helper.rb'
+
+ class CoreExtTest < Test::Unit::TestCase
+ end
+
+Navigate to your plugin directory and run `rake test`
+
+ cd vendor/plugins/yaffle
+ rake test
+
+Your test should fail with `no such file to load -- ./test/../lib/core_ext.rb (LoadError)` because we haven't created any file yet. Create the file `lib/core_ext.rb` and re-run the tests. You should see a different error message:
+
+ 1.) Failure ...
+ No tests were specified
+
+Great - now you are ready to start development. The first thing we'll do is to add a method to String called `to_squawk` which will prefix the string with the word "squawk! ". The test will look something like this:
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ class CoreExtTest < Test::Unit::TestCase
+ def test_string_should_respond_to_squawk
+ assert_equal true, "".respond_to?(:to_squawk)
+ end
+ def test_string_prepend_empty_strings_with_the_word_squawk
+ assert_equal "squawk!", "".to_squawk
+ end
+ def test_string_prepend_non_empty_strings_with_the_word_squawk
+ assert_equal "squawk! Hello World", "Hello World".to_squawk
+ end
+ end
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ require "core_ext"
+
+ # File: vendor/plugins/yaffle/lib/core_ext.rb
+
+ class String
+ # returns the current string, prefixed by "squawk!"
+ def to_squawk
+ "squawk! #{self}".strip
+ end
+ end
+
+To test that your method does what it says it does, run the unit tests. To make sure your code is picked up by
+
+To test this, fire up a console and start squawking:
+
+ script/console
+ >> "Hello World".to_squawk
+ => "squawk! Hello World"
+
+If that worked, congratulations! You just created your first test-driven plugin that extends a core ruby class.
+
+Adding an `acts_as_yaffle` method to ActiveRecord models
+-----------------------
+
+A common pattern in plugins is to add a method called `acts_as_something` to models. In this case, you want to write a method called `acts_as_yaffle` that adds a squawk method to your models.
+
+To keep things clean, create a new test file called `acts_as_yaffle_test.rb` in your plugin's test directory and require your test helper.
+
+ # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
+
+ require File.dirname(__FILE__) + '/test_helper.rb'
+
+ class Hickwall < ActiveRecord::Base
+ acts_as_yaffle
+ end
+
+ class ActsAsYaffleTest < Test::Unit::TestCase
+ end
+
+ # File: vendor/plugins/lib/acts_as_yaffle.rb
+
+ module Yaffle
+ end
+
+One of the most common plugin patterns for `acts_as_yaffle` plugins is to structure your file like so:
+
+ module Yaffle
+ def self.included(base)
+ base.send :extend, ClassMethods
+ end
+
+ module ClassMethods
+ # any method placed here will apply to classes, like Hickwall
+ def acts_as_something
+ send :include, InstanceMethods
+ end
+ end
+
+ module InstanceMethods
+ # any method placed here will apply to instaces, like @hickwall
+ end
+ end
+
+With structure you can easily separate the methods that will be used for the class (like `Hickwall.some_method`) and the instance (like `@hickwell.some_method`).
+
+Let's add class method named `acts_as_yaffle` - testing it out first. You already defined the ActiveRecord models in your test helper, so if you run tests now they will fail.
+
+Back in your `acts\_as\_yaffle` file, update ClassMethods like so:
+
+ module ClassMethods
+ def acts_as_yaffle(options = {})
+ send :include, InstanceMethods
+ end
+ end
+
+Now that test should pass. Since your plugin is going to work with field names, you need to allow people to define the field names, in case there is a naming conflict. You can write a few simple tests for this:
+
+ # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
+
+ require File.dirname(__FILE__) + '/test_helper.rb'
+
+ class ActsAsYaffleTest < Test::Unit::TestCase
+ def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
+ assert_equal "last_squawk", Hickwall.yaffle_text_field
+ end
+ def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
+ assert_equal "last_squawked_at", Hickwall.yaffle_date_field
+ end
+ def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
+ assert_equal "last_tweet", Wickwall.yaffle_text_field
+ end
+ def test_a_wickwalls_yaffle_date_field_should_be_last_tweeted_at
+ assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
+ end
+ end
+
+To make these tests pass, you could modify your `acts_as_yaffle` file like so:
+
+ # File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb
+
+ module Yaffle
+ def self.included(base)
+ base.send :extend, ClassMethods
+ end
+
+ module ClassMethods
+ def acts_as_yaffle(options = {})
+ cattr_accessor :yaffle_text_field, :yaffle_date_field
+ self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
+ self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
+ send :include, InstanceMethods
+ end
+ end
+
+ module InstanceMethods
+ end
+ end
+
+Now you can add tests for the instance methods, and the instance method itself:
+
+ # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
+
+ require File.dirname(__FILE__) + '/test_helper.rb'
+
+ class ActsAsYaffleTest < Test::Unit::TestCase
+
+ def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
+ assert_equal "last_squawk", Hickwall.yaffle_text_field
+ end
+ def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
+ assert_equal "last_squawked_at", Hickwall.yaffle_date_field
+ end
+
+ def test_a_wickwalls_yaffle_text_field_should_be_last_squawk
+ assert_equal "last_tweet", Wickwall.yaffle_text_field
+ end
+ def test_a_wickwalls_yaffle_date_field_should_be_last_squawked_at
+ assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
+ end
+
+ def test_hickwalls_squawk_should_populate_last_squawk
+ hickwall = Hickwall.new
+ hickwall.squawk("Hello World")
+ assert_equal "squawk! Hello World", hickwall.last_squawk
+ end
+ def test_hickwalls_squawk_should_populate_last_squawked_at
+ hickwall = Hickwall.new
+ hickwall.squawk("Hello World")
+ assert_equal Date.today, hickwall.last_squawked_at
+ end
+
+ def test_wickwalls_squawk_should_populate_last_tweet
+ wickwall = Wickwall.new
+ wickwall.squawk("Hello World")
+ assert_equal "squawk! Hello World", wickwall.last_tweet
+ end
+ def test_wickwalls_squawk_should_populate_last_tweeted_at
+ wickwall = Wickwall.new
+ wickwall.squawk("Hello World")
+ assert_equal Date.today, wickwall.last_tweeted_at
+ end
+ end
+
+ # File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb
+
+ module Yaffle
+ def self.included(base)
+ base.send :extend, ClassMethods
+ end
+
+ module ClassMethods
+ def acts_as_yaffle(options = {})
+ cattr_accessor :yaffle_text_field, :yaffle_date_field
+ self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
+ self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
+ send :include, InstanceMethods
+ end
+ end
+
+ module InstanceMethods
+ def squawk(string)
+ write_attribute(self.class.yaffle_text_field, string.to_squawk)
+ write_attribute(self.class.yaffle_date_field, Date.today)
+ end
+ end
+ end
+
+Note the use of write_attribute to write to the field in model.
+
+Create a view helper
+-----------------------
+
+Creating a view helper is a 3-step process:
+
+* Add an appropriately named file to the lib directory
+* Require the file and hooks in init.rb
+* Write the tests
+
+First, create the test to define the functionality you want:
+
+ # File: vendor/plugins/yaffle/test/view_helpers_test.rb
+
+ require File.dirname(__FILE__) + '/test_helper.rb'
+ include YaffleViewHelper
+
+ class ViewHelpersTest < Test::Unit::TestCase
+ def test_squawk_info_for_should_return_the_text_and_date
+ time = Time.now
+ hickwall = Hickwall.new
+ hickwall.last_squawk = "Hello World"
+ hickwall.last_squawked_at = time
+ assert_equal "Hello World, #{time.to_s}", squawk_info_for(hickwall)
+ end
+ end
+
+Then add the following statements to init.rb:
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ require "view_helpers"
+ ActionView::Base.send :include, YaffleViewHelper
+
+Then add the view helpers file and
+
+ # File: vendor/plugins/yaffle/lib/view_helpers.rb
+
+ module YaffleViewHelper
+ def squawk_info_for(yaffle)
+ returning "" do |result|
+ result << yaffle.read_attribute(yaffle.class.yaffle_text_field)
+ result << ", "
+ result << yaffle.read_attribute(yaffle.class.yaffle_date_field).to_s
+ end
+ end
+ end
+
+You can also test this in script/console by using the "helper" method:
+
+ script/console
+ >> helper.squawk_info_for(@some_yaffle_instance)
+
+Create a migration generator
+-----------------------
+
+When you created the plugin above, you specified the --with-generator option, so you already have the generator stubs in your plugin.
+
+We'll be relying on the built-in rails generate template for this tutorial. Going into the details of generators is beyond the scope of this tutorial.
+
+Type:
+
+ script/generate
+
+You should see the line:
+
+ Plugins (vendor/plugins): yaffle
+
+When you run `script/generate yaffle` you should see the contents of your USAGE file. For this plugin, the USAGE file looks like this:
+
+ Description:
+ Creates a migration that adds yaffle squawk fields to the given model
+
+ Example:
+ ./script/generate yaffle hickwall
+
+ This will create:
+ db/migrate/TIMESTAMP_add_yaffle_fields_to_hickwall
+
+Now you can add code to your generator:
+
+ # File: vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
+
+ class YaffleGenerator < Rails::Generator::NamedBase
+ def manifest
+ record do |m|
+ m.migration_template 'migration:migration.rb', "db/migrate", {:assigns => yaffle_local_assigns,
+ :migration_file_name => "add_yaffle_fields_to_#{custom_file_name}"
+ }
+ end
+ end
+
+ private
+ def custom_file_name
+ custom_name = class_name.underscore.downcase
+ custom_name = custom_name.pluralize if ActiveRecord::Base.pluralize_table_names
+ end
+
+ def yaffle_local_assigns
+ returning(assigns = {}) do
+ assigns[:migration_action] = "add"
+ assigns[:class_name] = "add_yaffle_fields_to_#{custom_file_name}"
+ assigns[:table_name] = custom_file_name
+ assigns[:attributes] = [Rails::Generator::GeneratedAttribute.new("last_squawk", "string")]
+ assigns[:attributes] << Rails::Generator::GeneratedAttribute.new("last_squawked_at", "datetime")
+ end
+ end
+ end
+
+Note that you need to be aware of whether or not table names are pluralized.
+
+This does a few things:
+
+* Reuses the built in rails migration_template method
+* Reuses the built-in rails migration template
+
+When you run the generator like
+
+ script/generate yaffle bird
+
+You will see a new file:
+
+ # File: db/migrate/20080529225649_add_yaffle_fields_to_birds.rb
+
+ class AddYaffleFieldsToBirds < ActiveRecord::Migration
+ def self.up
+ add_column :birds, :last_squawk, :string
+ add_column :birds, :last_squawked_at, :datetime
+ end
+
+ def self.down
+ remove_column :birds, :last_squawked_at
+ remove_column :birds, :last_squawk
+ end
+ end
+
+Adding custom generator commands
+------------------------
+
+You may have noticed above that you can used one of the built-in rails migration commands `m.migration_template`. You can create your own commands for these, using the following steps:
+
+1. Add the require and hook statements to init.rb
+2. Create the commands - creating 3 sets, Create, Destroy, List
+3. Add the method to your generator
+
+Working with the internals of generators is beyond the scope of this tutorial, but here is a basic example:
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ require "commands"
+ Rails::Generator::Commands::Create.send :include, Yaffle::Generator::Commands::Create
+ Rails::Generator::Commands::Destroy.send :include, Yaffle::Generator::Commands::Destroy
+ Rails::Generator::Commands::List.send :include, Yaffle::Generator::Commands::List
+
+ # File: vendor/plugins/yaffle/lib/commands.rb
+
+ require 'rails_generator'
+ require 'rails_generator/commands'
+
+ module Yaffle #:nodoc:
+ module Generator #:nodoc:
+ module Commands #:nodoc:
+ module Create
+ def yaffle_definition
+ file("definition.txt", "definition.txt")
+ end
+ end
+
+ module Destroy
+ def yaffle_definition
+ file("definition.txt", "definition.txt")
+ end
+ end
+
+ module List
+ def yaffle_definition
+ file("definition.txt", "definition.txt")
+ end
+ end
+ end
+ end
+ end
+
+ # File: vendor/plugins/yaffle/generators/yaffle/templates/definition.txt
+
+ Yaffle is a bird
+
+ # File: vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
+
+ class YaffleGenerator < Rails::Generator::NamedBase
+ def manifest
+ m.yaffle_definition
+ end
+ end
+ end
+
+This example just uses the built-in "file" method, but you could do anything that ruby allows.
+
+Adding Routes
+------------------------
+
+Testing routes in plugins can be complex, especially if the controllers are also in the plugin itself. Jamis Buck showed a great example of this in [http://weblog.jamisbuck.org/2006/10/26/monkey-patching-rails-extending-routes-2](http://weblog.jamisbuck.org/2006/10/26/monkey-patching-rails-extending-routes-2)
+
+ # File: vendor/plugins/yaffle/test/routing_test.rb
+
+ require "#{File.dirname(__FILE__)}/test_helper"
+
+ class RoutingTest < Test::Unit::TestCase
+
+ def setup
+ ActionController::Routing::Routes.draw do |map|
+ map.yaffles
+ end
+ end
+
+ def test_yaffles_route
+ assert_recognition :get, "/yaffles", :controller => "yaffles_controller", :action => "index"
+ end
+
+ private
+
+ # yes, I know about assert_recognizes, but it has proven problematic to
+ # use in these tests, since it uses RouteSet#recognize (which actually
+ # tries to instantiate the controller) and because it uses an awkward
+ # parameter order.
+ def assert_recognition(method, path, options)
+ result = ActionController::Routing::Routes.recognize_path(path, :method => method)
+ assert_equal options, result
+ end
+ end
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ require "routing"
+ ActionController::Routing::RouteSet::Mapper.send :include, Yaffle::Routing::MapperExtensions
+
+ # File: vendor/plugins/yaffle/lib/routing.rb
+
+ module Yaffle #:nodoc:
+ module Routing #:nodoc:
+ module MapperExtensions
+ def yaffles
+ @set.add_route("/yaffles", {:controller => "yaffles_controller", :action => "index"})
+ end
+ end
+ end
+ end
+
+ # File: config/routes.rb
+
+ ActionController::Routing::Routes.draw do |map|
+ ...
+ map.yaffles
+ end
+
+You can also see if your routes work by running `rake routes` from your app directory.
+
+Generate RDoc Documentation
+-----------------------
+
+Once your plugin is stable, the tests pass on all database and you are ready to deploy do everyone else a favor and document it! Luckily, writing documentation for your plugin is easy.
+
+The first step is to update the README file with detailed information about how to use your plugin. A few key things to include are:
+
+* Your name
+* How to install
+* How to add the functionality to the app (several examples of common use cases)
+* Warning, gotchas or tips that might help save users time
+
+Once your README is solid, go through and add rdoc comments to all of the methods that developers will use.
+
+Before you generate your documentation, be sure to go through and add nodoc comments to those modules and methods that are not important to your users.
+
+Once your comments are good to go, navigate to your plugin directory and run
+
+ rake rdoc
+
+Working with init.rb
+------------------------
+
+The plugin initializer script init.rb is invoked via `eval` (not require) so it has slightly different behavior.
+
+If you reopen any classes in init.rb itself your changes will potentially be made to the wrong module. There are 2 ways around this:
+
+The first way is to explicitly define the top-level module space for all modules and classes, like ::Hash
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ class ::Hash
+ def is_a_special_hash?
+ true
+ end
+ end
+
+OR you can use module\_eval or class\_eval
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ Hash.class_eval do
+ def is_a_special_hash?
+ true
+ end
+ end
+
+Storing models, views, helpers, and controllers in your plugins
+------------------------
+
+You can easily store models, views, helpers and controllers in plugins. Just create a folder for each in the lib folder, add them to the load path and remove them from the load once path:
+
+ # File: vendor/plugins/yaffle/init.rb
+
+ %w{ models controllers helpers }.each do |dir|
+ path = File.join(directory, 'lib', dir)
+ $LOAD_PATH << path
+ Dependencies.load_paths << path
+ Dependencies.load_once_paths.delete(path)
+ end
+
+Adding directories to the load path makes them appear just like files in the the main app directory - except that they are only loaded once, so you have to restart the web server to see the changes in the browser.
+
+Adding directories to the load once paths allow those changes to picked up as soon as you save the file - without having to restart the web server.
+
+Storing plugins in alternate locations
+-------------------------
+
+You can store plugins wherever you want - you just have to add those plugins to the plugins path in environment.rb
+
+Since the plugin is only loaded after the plugin paths are defined, you can't redefine this in your plugins - but it may be good to now.
+
+You can even store plugins inside of other plugins for complete plugin madness!
+
+ config.plugin_paths << File.join(RAILS_ROOT,"vendor","plugins","yaffle","lib","plugins")
+
+Plugin Loaders and Plugin Locators
+------------------------
+
+If the built-in plugin behavior is inadequate, you can change almost every aspect of the location and loading process. You can write your own plugin locators and plugin loaders, but that's beyond the scope of this tutorial.
+
+Custom Plugin Generators
+------------------------
+
+If you are an RSpec fan, you can install the rspec\_plugin\_generator, which will generate the spec folder and database for you.
+
+[http://github.com/pat-maddox/rspec-plugin-generator/tree/master](http://github.com/pat-maddox/rspec-plugin-generator/tree/master)
+
+References
+------------------------
+
+* [http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-i](http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-i)
+* [http://nubyonrails.com/articles/2006/05/09/the-complete-guide-to-rails-plugins-part-ii](http://nubyonrails.com/articles/2006/05/09/the-complete-guide-to-rails-plugins-part-ii)
+* [http://github.com/technoweenie/attachment_fu/tree/master](http://github.com/technoweenie/attachment_fu/tree/master)
+* [http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html](http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html)
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