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The Basics of Creating Rails Plugins

A Rails plugin is either an extension or a modification of the core framework. Plugins provide:

After reading this guide you should be familiar with:

This guide describes how to build a test-driven plugin that will:

For the purpose of this guide 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. First, you need to get setup for development.

1 Setup

1.1 Create the Basic Application

The examples in this guide require that you have a working rails application. To create a simple rails app execute:

gem install rails rails yaffle_guide cd yaffle_guide rails generate scaffold bird name:string rake db:migrate rails server

Then navigate to http://localhost:3000/birds. Make sure you have a functioning rails app before continuing.

The aforementioned instructions will work for sqlite3. For more detailed instructions on how to create a rails app for other databases see the API docs.

1.2 Generate the Plugin Skeleton

Rails ships with a plugin generator which creates a basic plugin skeleton. 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:

rails generate plugin yaffle rails generate plugin yaffle --with-generator

To get more detailed help on the plugin generator, type rails generate plugin.

Later on this guide will describe how to work with generators, so go ahead and generate your plugin with the --with-generator option now:

rails 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

1.3 Organize Your Files

To make it easy to organize your files and to make the plugin more compatible with GemPlugins, start out by altering your file system to look like this:

|-- lib | |-- yaffle | `-- yaffle.rb `-- rails | `-- init.rb
# vendor/plugins/yaffle/init.rb require 'yaffle'

Now you can add any require statements to lib/yaffle.rb and keep init.rb clean.

2 Tests

In this guide you will learn how to test your plugin against multiple different database adapters using Active Record. 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 method that sets up the database

2.1 Test Setup

# vendor/plugins/yaffle/test/database.yml sqlite: :adapter: sqlite :dbfile: vendor/plugins/yaffle/test/yaffle_plugin.sqlite.db sqlite3: :adapter: sqlite3 :dbfile: vendor/plugins/yaffle/test/yaffle_plugin.sqlite3.db postgresql: :adapter: postgresql :username: postgres :password: postgres :database: yaffle_plugin_test :min_messages: ERROR mysql: :adapter: mysql :host: localhost :username: root :password: password :database: yaffle_plugin_test

For this guide you’ll need 2 tables/models, Hickwalls and Wickwalls, so add the following:

# vendor/plugins/yaffle/test/schema.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 create_table :woodpeckers, :force => true do |t| t.string :name end end
# 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')) def load_schema 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__) + '/../rails/init' end

Now whenever you write a test that requires the database, you can call ‘load_schema’.

2.2 Run the Plugin Tests

Once you have these files in place, you can write your first test to ensure that your plugin-testing setup is correct. By default rails generates a file in vendor/plugins/yaffle/test/yaffle_test.rb with a sample test. Replace the contents of that file with:

# vendor/plugins/yaffle/test/yaffle_test.rb require File.dirname(__FILE__) + '/test_helper' class YaffleTest < Test::Unit::TestCase load_schema class Hickwall < ActiveRecord::Base end class Wickwall < ActiveRecord::Base end def test_schema_has_loaded_correctly assert_equal [], Hickwall.all assert_equal [], Wickwall.all end end

To run this, go to the plugin directory and run rake:

cd vendor/plugins/yaffle rake

You should see output like:

/opt/local/bin/ruby -Ilib:lib "/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.3/lib/rake/rake_test_loader.rb" "test/yaffle_test.rb" create_table(:hickwalls, {:force=>true}) -> 0.0220s -- create_table(:wickwalls, {:force=>true}) -> 0.0077s -- initialize_schema_migrations_table() -> 0.0007s -- assume_migrated_upto_version(0) -> 0.0007s Loaded suite /opt/local/lib/ruby/gems/1.8/gems/rake-0.8.3/lib/rake/rake_test_loader Started . Finished in 0.002236 seconds. 1 test, 1 assertion, 0 failures, 0 errors

By default the setup above runs your tests with sqlite or sqlite3. To run tests with one of the other connection strings specified in database.yml, pass the DB environment variable to rake:

rake DB=sqlite rake DB=sqlite3 rake DB=mysql rake DB=postgresql

Now you are ready to test-drive your plugin!

3 Extending Core Classes

This section will explain how to add a method to String that will be available anywhere in your rails app.

In this example you will add a method to String named to_squawk. To begin, create a new test file with a few assertions:

# vendor/plugins/yaffle/test/core_ext_test.rb require File.dirname(__FILE__) + '/test_helper' class CoreExtTest < Test::Unit::TestCase def test_to_squawk_prepends_the_word_squawk assert_equal "squawk! Hello World", "Hello World".to_squawk end end

Navigate to your plugin directory and run rake test:

cd vendor/plugins/yaffle rake test

The test above should fail with the message:

1) Error: test_to_squawk_prepends_the_word_squawk(CoreExtTest): NoMethodError: undefined method `to_squawk' for "Hello World":String ./test/core_ext_test.rb:5:in `test_to_squawk_prepends_the_word_squawk'

Great – now you are ready to start development.

Then in lib/yaffle.rb require lib/core_ext:

# vendor/plugins/yaffle/lib/yaffle.rb require "yaffle/core_ext"

Finally, create the core_ext.rb file and add the to_squawk method:

# vendor/plugins/yaffle/lib/yaffle/core_ext.rb String.class_eval do def to_squawk "squawk! #{self}".strip end end

To test that your method does what it says it does, run the unit tests with rake from your plugin directory. To see this in action, fire up a console and start squawking:

$ rails console >> "Hello World".to_squawk => "squawk! Hello World"

3.1 Working with init.rb

When Rails loads plugins it looks for a file named init.rb. However, when the plugin is initialized, init.rb is invoked via eval (not require) so it has slightly different behavior.

The plugins loader also looks for rails/init.rb, but that one is deprecated in favor of the top-level init.rb aforementioned.

Under certain circumstances if you reopen classes or modules in init.rb you may inadvertently create a new class, rather than reopening an existing class. A better alternative is to reopen the class in a different file, and require that file from init.rb, as shown above.

If you must reopen a class in init.rb you can use module_eval or class_eval to avoid any issues:

# vendor/plugins/yaffle/init.rb Hash.class_eval do def is_a_special_hash? true end end

Another way is to explicitly define the top-level module space for all modules and classes, like ::Hash:

# vendor/plugins/yaffle/init.rb class ::Hash def is_a_special_hash? true end end

4 Add an “acts_as” Method to Active Record

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 begin, set up your files so that you have:

  • vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
require File.dirname(__FILE__) + '/test_helper' class ActsAsYaffleTest < Test::Unit::TestCase end
  • vendor/plugins/yaffle/lib/yaffle.rb
require 'yaffle/acts_as_yaffle'
  • vendor/plugins/yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle # your code will go here end

Note that after requiring ‘acts_as_yaffle’ you also have to include it into ActiveRecord::Base so that your plugin methods will be available to the rails models.

One of the most common plugin patterns for ‘acts_as_yaffle’ plugins is to structure your file like so:

  • vendor/plugins/yaffle/lib/yaffle/acts_as_yaffle.rb
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).

4.1 Add a Class Method

This plugin will expect that you’ve added a method to your model named ‘last_squawk’. However, the plugin users might have already defined a method on their model named ‘last_squawk’ that they use for something else. This plugin will allow the name to be changed by adding a class method called ‘yaffle_text_field’.

To start out, write a failing test that shows the behavior you’d like:

  • vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
require File.dirname(__FILE__) + '/test_helper' class Hickwall < ActiveRecord::Base acts_as_yaffle end class Wickwall < ActiveRecord::Base acts_as_yaffle :yaffle_text_field => :last_tweet end class ActsAsYaffleTest < Test::Unit::TestCase load_schema def test_a_hickwalls_yaffle_text_field_should_be_last_squawk assert_equal "last_squawk", Hickwall.yaffle_text_field end def test_a_wickwalls_yaffle_text_field_should_be_last_tweet assert_equal "last_tweet", Wickwall.yaffle_text_field end end

To make these tests pass, you could modify your acts_as_yaffle file like so:

  • vendor/plugins/yaffle/lib/yaffle/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 self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s end end end ActiveRecord::Base.send :include, Yaffle

4.2 Add an Instance Method

This plugin will add a method named ‘squawk’ to any Active Record objects that call ‘acts_as_yaffle’. The ‘squawk’ method will simply set the value of one of the fields in the database.

To start out, write a failing test that shows the behavior you’d like:

  • vendor/plugins/yaffle/test/acts_as_yaffle_test.rb
require File.dirname(__FILE__) + '/test_helper' class Hickwall < ActiveRecord::Base acts_as_yaffle end class Wickwall < ActiveRecord::Base acts_as_yaffle :yaffle_text_field => :last_tweet end class ActsAsYaffleTest < Test::Unit::TestCase load_schema def test_a_hickwalls_yaffle_text_field_should_be_last_squawk assert_equal "last_squawk", Hickwall.yaffle_text_field end def test_a_wickwalls_yaffle_text_field_should_be_last_tweet assert_equal "last_tweet", Wickwall.yaffle_text_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_wickwalls_squawk_should_populate_last_tweeted_at wickwall = Wickwall.new wickwall.squawk("Hello World") assert_equal "squawk! Hello World", wickwall.last_tweet end end

Run this test to make sure the last two tests fail, then update ‘acts_as_yaffle.rb’ to look like this:

  • vendor/plugins/yaffle/lib/yaffle/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 self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s send :include, InstanceMethods end end module InstanceMethods def squawk(string) write_attribute(self.class.yaffle_text_field, string.to_squawk) end end end ActiveRecord::Base.send :include, Yaffle

The use of write_attribute to write to the field in model is just one example of how a plugin can interact with the model, and will not always be the right method to use. For example, you could also use send("#{self.class.yaffle_text_field}=", string.to_squawk).

5 Models

This section describes how to add a model named ‘Woodpecker’ to your plugin that will behave the same as a model in your main app. When storing models, controllers, views and helpers in your plugin, it’s customary to keep them in directories that match the rails directories. For this example, create a file structure like this:

vendor/plugins/yaffle/ |-- lib | |-- app | | |-- controllers | | |-- helpers | | |-- models | | | `-- woodpecker.rb | | `-- views | |-- yaffle | | |-- acts_as_yaffle.rb | | |-- commands.rb | | `-- core_ext.rb | `-- yaffle.rb

As always, start with a test:

  • vendor/plugins/yaffle/test/woodpecker_test.rb:
require File.dirname(__FILE__) + '/test_helper' class WoodpeckerTest < Test::Unit::TestCase load_schema def test_woodpecker assert_kind_of Woodpecker, Woodpecker.new end end

This is just a simple test to make sure the class is being loaded correctly. After watching it fail with rake, you can make it pass like so:

  • vendor/plugins/yaffle/lib/yaffle.rb:
%w{ models }.each do |dir| path = File.join(File.dirname(__FILE__), 'app', dir) $LOAD_PATH << path ActiveSupport::Dependencies.load_paths << path ActiveSupport::Dependencies.load_once_paths.delete(path) end

Adding directories to the load path makes them appear just like files in 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. Removing directories from the ‘load_once_paths’ allow those changes to picked up as soon as you save the file – without having to restart the web server. This is particularly useful as you develop the plugin.

  • vendor/plugins/yaffle/lib/app/models/woodpecker.rb:
class Woodpecker < ActiveRecord::Base end

Finally, add the following to your plugin’s ‘schema.rb’:

  • vendor/plugins/yaffle/test/schema.rb:
create_table :woodpeckers, :force => true do |t| t.string :name end

Now your test should be passing, and you should be able to use the Woodpecker model from within your rails app, and any changes made to it are reflected immediately when running in development mode.

6 Controllers

This section describes how to add a controller named ‘woodpeckers’ to your plugin that will behave the same as a controller in your main app. This is very similar to adding a model.

You can test your plugin’s controller as you would test any other controller:

  • vendor/plugins/yaffle/test/woodpeckers_controller_test.rb:
require File.dirname(__FILE__) + '/test_helper' require 'woodpeckers_controller' require 'action_controller/test_process' class WoodpeckersController; def rescue_action(e) raise e end; end class WoodpeckersControllerTest < Test::Unit::TestCase def setup @controller = WoodpeckersController.new @request = ActionController::TestRequest.new @response = ActionController::TestResponse.new ActionController::Routing::Routes.draw do |map| map.resources :woodpeckers end end def test_index get :index assert_response :success end end

This is just a simple test to make sure the controller is being loaded correctly. After watching it fail with rake, you can make it pass like so:

  • vendor/plugins/yaffle/lib/yaffle.rb:
%w{ models controllers }.each do |dir| path = File.join(File.dirname(__FILE__), 'app', dir) $LOAD_PATH << path ActiveSupport::Dependencies.load_paths << path ActiveSupport::Dependencies.load_once_paths.delete(path) end
  • vendor/plugins/yaffle/lib/app/controllers/woodpeckers_controller.rb:
class WoodpeckersController < ActionController::Base def index render :text => "Squawk!" end end

Now your test should be passing, and you should be able to use the Woodpeckers controller in your app. If you add a route for the woodpeckers controller you can start up your server and go to http://localhost:3000/woodpeckers to see your controller in action.

7 Helpers

This section describes how to add a helper named ‘WoodpeckersHelper’ to your plugin that will behave the same as a helper in your main app. This is very similar to adding a model and a controller.

You can test your plugin’s helper as you would test any other helper:

  • vendor/plugins/yaffle/test/woodpeckers_helper_test.rb
require File.dirname(__FILE__) + '/test_helper' include WoodpeckersHelper class WoodpeckersHelperTest < Test::Unit::TestCase def test_tweet assert_equal "Tweet! Hello", tweet("Hello") end end

This is just a simple test to make sure the helper is being loaded correctly. After watching it fail with rake, you can make it pass like so:

  • vendor/plugins/yaffle/lib/yaffle.rb:
%w{ models controllers helpers }.each do |dir| path = File.join(File.dirname(__FILE__), 'app', dir) $LOAD_PATH << path ActiveSupport::Dependencies.load_paths << path ActiveSupport::Dependencies.load_once_paths.delete(path) end
  • vendor/plugins/yaffle/lib/app/helpers/woodpeckers_helper.rb:
module WoodpeckersHelper def tweet(text) "Tweet! #{text}" end end

Now your test should be passing, and you should be able to use the Woodpeckers helper in your app.

8 Routes

In a standard ‘routes.rb’ file you use routes like ‘map.connect’ or ‘map.resources’. You can add your own custom routes from a plugin. This section will describe how to add a custom method called that can be called with ‘map.yaffles’.

Testing routes from plugins is slightly different from testing routes in a standard rails app. To begin, add a test like this:

  • 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 def assert_recognition(method, path, options) result = ActionController::Routing::Routes.recognize_path(path, :method => method) assert_equal options, result end end

Once you see the tests fail by running ‘rake’, you can make them pass with:

  • vendor/plugins/yaffle/lib/yaffle.rb
require "yaffle/routing"
  • vendor/plugins/yaffle/lib/yaffle/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 ActionController::Routing::RouteSet::Mapper.send :include, Yaffle::Routing::MapperExtensions
  • 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.

9 Generators

Many plugins ship with generators. When you created the plugin above, you specified the --with-generator option, so you already have the generator stubs in ‘vendor/plugins/yaffle/generators/yaffle’.

Building generators is a complex topic unto itself and this section will cover one small aspect of generators: generating a simple text file.

9.1 Testing Generators

Many rails plugin authors do not test their generators, however testing generators is quite simple. A typical generator test does the following:

  • Creates a new fake rails root directory that will serve as destination
  • Runs the generator
  • Asserts that the correct files were generated
  • Removes the fake rails root

This section will describe how to create a simple generator that adds a file. For the generator in this section, the test could look something like this:

  • vendor/plugins/yaffle/test/definition_generator_test.rb
require File.dirname(__FILE__) + '/test_helper' require 'rails_generator' require 'rails_generator/scripts/generate' class DefinitionGeneratorTest < Test::Unit::TestCase def setup FileUtils.mkdir_p(fake_rails_root) @original_files = file_list end def teardown FileUtils.rm_r(fake_rails_root) end def test_generates_correct_file_name Rails::Generator::Scripts::Generate.new.run(["yaffle_definition"], :destination => fake_rails_root) new_file = (file_list - @original_files).first assert_equal "definition.txt", File.basename(new_file) end private def fake_rails_root File.join(File.dirname(__FILE__), 'rails_root') end def file_list Dir.glob(File.join(fake_rails_root, "*")) end end

You can run ‘rake’ from the plugin directory to see this fail. Unless you are doing more advanced generator commands it typically suffices to just test the Generate script, and trust that rails will handle the Destroy and Update commands for you.

To make it pass, create the generator:

  • vendor/plugins/yaffle/generators/yaffle_definition/yaffle_definition_generator.rb
class YaffleDefinitionGenerator < Rails::Generator::Base def manifest record do |m| m.file "definition.txt", "definition.txt" end end end

9.2 The USAGE File

If you plan to distribute your plugin, developers will expect at least a minimum of documentation. You can add simple documentation to the generator by updating the USAGE file.

Rails ships with several built-in generators. You can see all of the generators available to you by typing the following at the command line:

rails generate

You should see something like this:

Installed Generators Plugins (vendor/plugins): yaffle_definition Builtin: controller, integration_test, mailer, migration, model, observer, plugin, resource, scaffold, session_migration

When you run rails generate yaffle_definition -h you should see the contents of your ‘vendor/plugins/yaffle/generators/yaffle_definition/USAGE’.

For this plugin, update the USAGE file could look like this:

Description: Adds a file with the definition of a Yaffle to the app's main directory

10 Add a Custom Generator Command

You may have noticed above that you can used one of the built-in rails migration commands migration_template. If your plugin needs to add and remove lines of text from existing files you will need to write your own generator methods.

This section describes how you you can create your own commands to add and remove a line of text from ‘routes.rb’. This example creates a very simple method that adds or removes a text file.

To start, add the following test method:

  • vendor/plugins/yaffle/test/generator_test.rb
def test_generates_definition Rails::Generator::Scripts::Generate.new.run(["yaffle", "bird"], :destination => fake_rails_root) definition = File.read(File.join(fake_rails_root, "definition.txt")) assert_match /Yaffle\:/, definition end

Run rake to watch the test fail, then make the test pass add the following:

  • vendor/plugins/yaffle/generators/yaffle/templates/definition.txt
Yaffle: A bird
  • vendor/plugins/yaffle/lib/yaffle.rb
require "yaffle/commands"
  • 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 module Update def yaffle_definition file("definition.txt", "definition.txt") end end end end end 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 Rails::Generator::Commands::Update.send :include, Yaffle::Generator::Commands::Update

Finally, call your new method in the manifest:

  • vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
class YaffleGenerator < Rails::Generator::NamedBase def manifest m.yaffle_definition end end

11 Generator Commands

You may have noticed above that you can used one of the built-in rails migration commands migration_template. If your plugin needs to add and remove lines of text from existing files you will need to write your own generator methods.

This section describes how you you can create your own commands to add and remove a line of text from ‘config/routes.rb’.

To start, add the following test method:

  • vendor/plugins/yaffle/test/route_generator_test.rb
require File.dirname(__FILE__) + '/test_helper' require 'rails_generator' require 'rails_generator/scripts/generate' require 'rails_generator/scripts/destroy' class RouteGeneratorTest < Test::Unit::TestCase def setup FileUtils.mkdir_p(File.join(fake_rails_root, "config")) end def teardown FileUtils.rm_r(fake_rails_root) end def test_generates_route content = <<-END ActionController::Routing::Routes.draw do |map| map.connect ':controller/:action/:id' map.connect ':controller/:action/:id.:format' end END File.open(routes_path, 'wb') {|f| f.write(content) } Rails::Generator::Scripts::Generate.new.run(["yaffle_route"], :destination => fake_rails_root) assert_match /map\.yaffles/, File.read(routes_path) end def test_destroys_route content = <<-END ActionController::Routing::Routes.draw do |map| map.yaffles map.connect ':controller/:action/:id' map.connect ':controller/:action/:id.:format' end END File.open(routes_path, 'wb') {|f| f.write(content) } Rails::Generator::Scripts::Destroy.new.run(["yaffle_route"], :destination => fake_rails_root) assert_no_match /map\.yaffles/, File.read(routes_path) end private def fake_rails_root File.join(File.dirname(__FILE__), "rails_root") end def routes_path File.join(fake_rails_root, "config", "routes.rb") end end

Run rake to watch the test fail, then make the test pass add the following:

  • vendor/plugins/yaffle/lib/yaffle.rb
require "yaffle/commands"
  • vendor/plugins/yaffle/lib/yaffle/commands.rb
require 'rails_generator' require 'rails_generator/commands' module Yaffle #:nodoc: module Generator #:nodoc: module Commands #:nodoc: module Create def yaffle_route logger.route "map.yaffle" look_for = 'ActionController::Routing::Routes.draw do |map|' unless options[:pretend] gsub_file('config/routes.rb', /(#{Regexp.escape(look_for)})/mi){|match| "#{match}\n map.yaffles\n"} end end end module Destroy def yaffle_route logger.route "map.yaffle" gsub_file 'config/routes.rb', /\n.+?map\.yaffles/mi, '' end end module List def yaffle_route end end module Update def yaffle_route end end end end end 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 Rails::Generator::Commands::Update.send :include, Yaffle::Generator::Commands::Update
  • vendor/plugins/yaffle/generators/yaffle_route/yaffle_route_generator.rb
class YaffleRouteGenerator < Rails::Generator::Base def manifest record do |m| m.yaffle_route end end end

To see this work, type:

rails generate yaffle_route rails destroy yaffle_route

If you haven’t set up the custom route from above, ‘rails destroy’ will fail and you’ll have to remove it manually.

12 Migrations

If your plugin requires changes to the app’s database you will likely want to somehow add migrations. Rails does not include any built-in support for calling migrations from plugins, but you can still make it easy for developers to call migrations from plugins.

If you have a very simple needs, like creating a table that will always have the same name and columns, then you can use a more simple solution, like creating a custom rake task or method. If your migration needs user input to supply table names or other options, you probably want to opt for generating a migration.

Let’s say you have the following migration in your plugin:

  • vendor/plugins/yaffle/lib/db/migrate/20081116181115_create_birdhouses.rb:
class CreateBirdhouses < ActiveRecord::Migration def self.up create_table :birdhouses, :force => true do |t| t.string :name t.timestamps end end def self.down drop_table :birdhouses end end

Here are a few possibilities for how to allow developers to use your plugin migrations:

12.1 Create a Custom Rake Task

  • vendor/plugins/yaffle/tasks/yaffle_tasks.rake:
namespace :db do namespace :migrate do description = "Migrate the database through scripts in vendor/plugins/yaffle/lib/db/migrate" description << "and update db/schema.rb by invoking db:schema:dump." description << "Target specific version with VERSION=x. Turn off output with VERBOSE=false." desc description task :yaffle => :environment do ActiveRecord::Migration.verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true ActiveRecord::Migrator.migrate("vendor/plugins/yaffle/lib/db/migrate/", ENV["VERSION"] ? ENV["VERSION"].to_i : nil) Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby end end end

12.2 Call Migrations Directly

  • vendor/plugins/yaffle/lib/yaffle.rb:
Dir.glob(File.join(File.dirname(__FILE__), "db", "migrate", "*")).each do |file| require file end
  • db/migrate/20081116181115_create_birdhouses.rb:
class CreateBirdhouses < ActiveRecord::Migration def self.up Yaffle::CreateBirdhouses.up end def self.down Yaffle::CreateBirdhouses.down end end

several plugin frameworks such as Desert and Engines provide more advanced plugin functionality.

12.3 Generate Migrations

Generating migrations has several advantages over other methods. Namely, you can allow other developers to more easily customize the migration. The flow looks like this:

  • call your rails generate script and pass in whatever options they need
  • examine the generated migration, adding/removing columns or other options as necessary

This example will demonstrate how to use one of the built-in generator methods named ‘migration_template’ to create a migration file. Extending the rails migration generator requires a somewhat intimate knowledge of the migration generator internals, so it’s best to write a test first:

  • vendor/plugins/yaffle/test/yaffle_migration_generator_test.rb
require File.dirname(__FILE__) + '/test_helper' require 'rails_generator' require 'rails_generator/scripts/generate' class MigrationGeneratorTest < Test::Unit::TestCase def setup FileUtils.mkdir_p(fake_rails_root) @original_files = file_list end def teardown ActiveRecord::Base.pluralize_table_names = true FileUtils.rm_r(fake_rails_root) end def test_generates_correct_file_name Rails::Generator::Scripts::Generate.new.run(["yaffle_migration", "some_name_nobody_is_likely_to_ever_use_in_a_real_migration"], :destination => fake_rails_root) new_file = (file_list - @original_files).first assert_match /add_yaffle_fields_to_some_name_nobody_is_likely_to_ever_use_in_a_real_migrations/, new_file assert_match /add_column :some_name_nobody_is_likely_to_ever_use_in_a_real_migrations do |t|/, File.read(new_file) end def test_pluralizes_properly ActiveRecord::Base.pluralize_table_names = false Rails::Generator::Scripts::Generate.new.run(["yaffle_migration", "some_name_nobody_is_likely_to_ever_use_in_a_real_migration"], :destination => fake_rails_root) new_file = (file_list - @original_files).first assert_match /add_yaffle_fields_to_some_name_nobody_is_likely_to_ever_use_in_a_real_migration/, new_file assert_match /add_column :some_name_nobody_is_likely_to_ever_use_in_a_real_migration do |t|/, File.read(new_file) end private def fake_rails_root File.join(File.dirname(__FILE__), 'rails_root') end def file_list Dir.glob(File.join(fake_rails_root, "db", "migrate", "*")) end end

the migration generator checks to see if a migation already exists, and it’s hard-coded to check the ‘db/migrate’ directory. As a result, if your test tries to generate a migration that already exists in the app, it will fail. The easy workaround is to make sure that the name you generate in your test is very unlikely to actually appear in the app.

After running the test with ‘rake’ you can make it pass with:

  • vendor/plugins/yaffle/generators/yaffle_migration/yaffle_migration_generator.rb
class YaffleMigrationGenerator < 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 custom_name 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")] end end end

The generator creates a new file in ‘db/migrate’ with a timestamp and an ‘add_column’ statement. It reuses the built-in rails migration_template method, and reuses the built-in rails migration template.

It’s courteous to check to see if table names are being pluralized whenever you create a generator that needs to be aware of table names. This way people using your generator won’t have to manually change the generated files if they’ve turned pluralization off.

To run the generator, type the following at the command line:

rails generate yaffle_migration bird

and you will see a new file:

  • db/migrate/20080529225649_add_yaffle_fields_to_birds.rb
class AddYaffleFieldsToBirds < ActiveRecord::Migration def self.up add_column :birds, :last_squawk, :string end def self.down remove_column :birds, :last_squawk end end

13 Rake tasks

When you created the plugin with the built-in rails generator, it generated a rake file for you in ‘vendor/plugins/yaffle/tasks/yaffle_tasks.rake’. Any rake task you add here will be available to the app.

Many plugin authors put all of their rake tasks into a common namespace that is the same as the plugin, like so:

  • vendor/plugins/yaffle/tasks/yaffle_tasks.rake
namespace :yaffle do desc "Prints out the word 'Yaffle'" task :squawk => :environment do puts "squawk!" end end

When you run rake -T from your plugin you will see:

yaffle:squawk # Prints out the word 'Yaffle'

You can add as many files as you want in the tasks directory, and if they end in .rake Rails will pick them up.

Note that tasks from vendor/plugins/yaffle/Rakefile are not available to the main app.

14 Plugins as Gems

Turning your rails plugin into a gem is a simple and straightforward task. This section will cover how to turn your plugin into a gem. It will not cover how to distribute that gem.

The initialization file has to be called rails/init.rb, the root init.rb file, if any, is ignored by Rails. Also, the name of the plugin now is relevant since config.gem tries to load it. Either name the main file after your gem, or document that users should use the :lib option.

It’s common practice to put any developer-centric rake tasks (such as tests, rdoc and gem package tasks) in Rakefile. A rake task that packages the gem might look like this:

  • vendor/plugins/yaffle/Rakefile:
PKG_FILES = FileList[ '[a-zA-Z]*', 'generators/**/*', 'lib/**/*', 'rails/**/*', 'tasks/**/*', 'test/**/*' ] spec = Gem::Specification.new do |s| s.name = "yaffle" s.version = "0.0.1" s.author = "Gleeful Yaffler" s.email = "yaffle@example.com" s.homepage = "http://yafflers.example.com/" s.platform = Gem::Platform::RUBY s.summary = "Sharing Yaffle Goodness" s.files = PKG_FILES.to_a s.require_path = "lib" s.has_rdoc = false s.extra_rdoc_files = ["README"] end desc 'Turn this plugin into a gem.' Rake::GemPackageTask.new(spec) do |pkg| pkg.gem_spec = spec end

To build and install the gem locally, run the following commands:

cd vendor/plugins/yaffle rake gem sudo gem install pkg/yaffle-0.0.1.gem

To test this, create a new rails app, add config.gem "yaffle" to config/environment.rb and all of your plugin’s functionality will be available to you.

15 RDoc Documentation

Once your plugin is stable 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. It’s also customary to add ‘#:nodoc:’ comments to those parts of the code that are not part of the public api.

Once your comments are good to go, navigate to your plugin directory and run:

rake rdoc

16 Appendix

If you prefer to use RSpec instead of Test::Unit, you may be interested in the RSpec Plugin Generator.

16.1 References

  • http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-i
  • http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-ii
  • http://github.com/technoweenie/attachment_fu/tree/master
  • http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html
  • http://www.mbleigh.com/2008/6/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins
  • http://weblog.jamisbuck.org/2006/10/26/monkey-patching-rails-extending-routes-2.

16.2 Contents of lib/yaffle.rb

  • vendor/plugins/yaffle/lib/yaffle.rb:
require "yaffle/core_ext" require "yaffle/acts_as_yaffle" require "yaffle/commands" require "yaffle/routing" %w{ models controllers helpers }.each do |dir| path = File.join(File.dirname(__FILE__), 'app', dir) $LOAD_PATH << path ActiveSupport::Dependencies.load_paths << path ActiveSupport::Dependencies.load_once_paths.delete(path) end # optionally: # Dir.glob(File.join(File.dirname(__FILE__), "db", "migrate", "*")).each do |file| # require file # end

16.3 Final Plugin Directory Structure

The final plugin should have a directory structure that looks something like this:

|-- MIT-LICENSE |-- README |-- Rakefile |-- generators | |-- yaffle_definition | | |-- USAGE | | |-- templates | | | `-- definition.txt | | `-- yaffle_definition_generator.rb | |-- yaffle_migration | | |-- USAGE | | |-- templates | | `-- yaffle_migration_generator.rb | `-- yaffle_route | |-- USAGE | |-- templates | `-- yaffle_route_generator.rb |-- install.rb |-- lib | |-- app | | |-- controllers | | | `-- woodpeckers_controller.rb | | |-- helpers | | | `-- woodpeckers_helper.rb | | `-- models | | `-- woodpecker.rb | |-- db | | `-- migrate | | `-- 20081116181115_create_birdhouses.rb | |-- yaffle | | |-- acts_as_yaffle.rb | | |-- commands.rb | | |-- core_ext.rb | | `-- routing.rb | `-- yaffle.rb |-- pkg | `-- yaffle-0.0.1.gem |-- rails | `-- init.rb |-- tasks | `-- yaffle_tasks.rake |-- test | |-- acts_as_yaffle_test.rb | |-- core_ext_test.rb | |-- database.yml | |-- debug.log | |-- definition_generator_test.rb | |-- migration_generator_test.rb | |-- route_generator_test.rb | |-- routes_test.rb | |-- schema.rb | |-- test_helper.rb | |-- woodpecker_test.rb | |-- woodpeckers_controller_test.rb | |-- wookpeckers_helper_test.rb | |-- yaffle_plugin.sqlite3.db | `-- yaffle_test.rb `-- uninstall.rb

17 Changelog

Lighthouse ticket

  • April 4, 2010: Fixed document to validate XHTML 1.0 Strict. Jaime Iniesta
  • November 17, 2008: Major revision by Jeff Dean