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diff --git a/guides/source/plugins.md b/guides/source/plugins.md new file mode 100644 index 0000000000..489bd227cd --- /dev/null +++ b/guides/source/plugins.md @@ -0,0 +1,444 @@ +The Basics of Creating Rails Plugins +==================================== + +A Rails plugin is either an extension or a modification of the core framework. Plugins provide: + +* A way for developers to share bleeding-edge ideas without hurting the stable code base. +* A segmented architecture so that units of code can be fixed or updated on their own release schedule. +* An outlet for the core developers so that they don't have to include every cool new feature under the sun. + +After reading this guide, you will know: + +* How to create a plugin from scratch. +* How to write and run tests for the plugin. + +This guide describes how to build a test-driven plugin that will: + +* Extend core Ruby classes like Hash and String. +* Add methods to `ActiveRecord::Base` in the tradition of the `acts_as` plugins. +* Give you information about where to put generators in your plugin. + +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. + +-------------------------------------------------------------------------------- + +Setup +----- + +Currently, Rails plugins are built as gems, _gemified plugins_. They can be shared across +different rails applications using RubyGems and Bundler if desired. + +### Generate a gemified plugin. + + +Rails ships with a `rails plugin new` command which creates a +skeleton for developing any kind of Rails extension with the ability +to run integration tests using a dummy Rails application. Create your +plugin with the command: + +```bash +$ bin/rails plugin new yaffle +``` + +See usage and options by asking for help: + +```bash +$ bin/rails plugin new --help +``` + +Testing Your Newly Generated Plugin +----------------------------------- + +You can navigate to the directory that contains the plugin, run the `bundle install` command + and run the one generated test using the `rake` command. + +You should see: + +```bash + 2 tests, 2 assertions, 0 failures, 0 errors, 0 skips +``` + +This will tell you that everything got generated properly and you are ready to start adding functionality. + +Extending Core Classes +---------------------- + +This section will explain how to add a method to String that will be available anywhere in your rails application. + +In this example you will add a method to String named `to_squawk`. To begin, create a new test file with a few assertions: + +```ruby +# yaffle/test/core_ext_test.rb + +require 'test_helper' + +class CoreExtTest < ActiveSupport::TestCase + def test_to_squawk_prepends_the_word_squawk + assert_equal "squawk! Hello World", "Hello World".to_squawk + end +end +``` + +Run `rake` to run the test. This test should fail because we haven't implemented the `to_squawk` method: + +```bash + 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. + +In `lib/yaffle.rb`, add `require 'yaffle/core_ext'`: + +```ruby +# yaffle/lib/yaffle.rb + +require 'yaffle/core_ext' + +module Yaffle +end +``` + +Finally, create the `core_ext.rb` file and add the `to_squawk` method: + +```ruby +# 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. + +```bash + 3 tests, 3 assertions, 0 failures, 0 errors, 0 skips +``` + +To see this in action, change to the test/dummy directory, fire up a console and start squawking: + +```bash +$ bin/rails console +>> "Hello World".to_squawk +=> "squawk! Hello World" +``` + +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 Active Record models. + +To begin, set up your files so that you have: + +```ruby +# yaffle/test/acts_as_yaffle_test.rb + +require 'test_helper' + +class ActsAsYaffleTest < ActiveSupport::TestCase +end +``` + +```ruby +# yaffle/lib/yaffle.rb + +require 'yaffle/core_ext' +require 'yaffle/acts_as_yaffle' + +module Yaffle +end +``` + +```ruby +# yaffle/lib/yaffle/acts_as_yaffle.rb + +module Yaffle + module ActsAsYaffle + # your code will go here + end +end +``` + +### 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: + +```ruby +# yaffle/test/acts_as_yaffle_test.rb + +require 'test_helper' + +class ActsAsYaffleTest < ActiveSupport::TestCase + + 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 +``` + +When you run `rake`, you should see the following: + +``` + 1) Error: + test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest): + NameError: uninitialized constant ActsAsYaffleTest::Hickwall + test/acts_as_yaffle_test.rb:6:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk' + + 2) Error: + test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest): + NameError: uninitialized constant ActsAsYaffleTest::Wickwall + test/acts_as_yaffle_test.rb:10:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet' + + 5 tests, 3 assertions, 0 failures, 2 errors, 0 skips +``` + +This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test. +We can easily generate these models in our "dummy" Rails application by running the following commands from the +test/dummy directory: + +```bash +$ cd test/dummy +$ bin/rails generate model Hickwall last_squawk:string +$ bin/rails generate model Wickwall last_squawk:string last_tweet:string +``` + +Now you can create the necessary database tables in your testing database by navigating to your dummy app +and migrating the database. First, run: + +```bash +$ cd test/dummy +$ bin/rake db:migrate +``` + +While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act +like yaffles. + +```ruby +# test/dummy/app/models/hickwall.rb + +class Hickwall < ActiveRecord::Base + acts_as_yaffle +end + +# test/dummy/app/models/wickwall.rb + +class Wickwall < ActiveRecord::Base + acts_as_yaffle yaffle_text_field: :last_tweet +end + +``` + +We will also add code to define the `acts_as_yaffle` method. + +```ruby +# yaffle/lib/yaffle/acts_as_yaffle.rb +module Yaffle + module ActsAsYaffle + extend ActiveSupport::Concern + + included do + end + + module ClassMethods + def acts_as_yaffle(options = {}) + # your code will go here + end + end + end +end + +ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle +``` + +You can then return to the root directory (`cd ../..`) of your plugin and rerun the tests using `rake`. + +``` + 1) Error: + test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest): + NoMethodError: undefined method `yaffle_text_field' for #<Class:0x000001016661b8> + /Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing' + test/acts_as_yaffle_test.rb:5:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk' + + 2) Error: + test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest): + NoMethodError: undefined method `yaffle_text_field' for #<Class:0x00000101653748> + Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing' + test/acts_as_yaffle_test.rb:9:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet' + + 5 tests, 3 assertions, 0 failures, 2 errors, 0 skips + +``` + +Getting closer... Now we will implement the code of the `acts_as_yaffle` method to make the tests pass. + +```ruby +# yaffle/lib/yaffle/acts_as_yaffle.rb + +module Yaffle + module ActsAsYaffle + extend ActiveSupport::Concern + + included do + 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 +end + +ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle +``` + +When you run `rake`, you should see the tests all pass: + +```bash + 5 tests, 5 assertions, 0 failures, 0 errors, 0 skips +``` + +### Add an Instance Method + +This plugin will add a method named 'squawk' to any Active Record object that calls '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: + +```ruby +# yaffle/test/acts_as_yaffle_test.rb +require 'test_helper' + +class ActsAsYaffleTest < ActiveSupport::TestCase + + 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_tweet + wickwall = Wickwall.new + wickwall.squawk("Hello World") + assert_equal "squawk! Hello World", wickwall.last_tweet + end +end +``` + +Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method `squawk'", +then update 'acts_as_yaffle.rb' to look like this: + +```ruby +# yaffle/lib/yaffle/acts_as_yaffle.rb + +module Yaffle + module ActsAsYaffle + extend ActiveSupport::Concern + + included do + 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 + + include Yaffle::ActsAsYaffle::LocalInstanceMethods + end + end + + module LocalInstanceMethods + def squawk(string) + write_attribute(self.class.yaffle_text_field, string.to_squawk) + end + end + end +end + +ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle +``` + +Run `rake` one final time and you should see: + +``` + 7 tests, 7 assertions, 0 failures, 0 errors, 0 skips +``` + +NOTE: 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: + +```ruby +send("#{self.class.yaffle_text_field}=", string.to_squawk) +``` + +Generators +---------- + +Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about +the creation of generators can be found in the [Generators Guide](generators.html) + +Publishing Your Gem +------------------- + +Gem plugins currently in development can easily be shared from any Git repository. To share the Yaffle gem with others, simply +commit the code to a Git repository (like GitHub) and add a line to the Gemfile of the application in question: + +```ruby +gem 'yaffle', git: 'git://github.com/yaffle_watcher/yaffle.git' +``` + +After running `bundle install`, your gem functionality will be available to the application. + +When the gem is ready to be shared as a formal release, it can be published to [RubyGems](http://www.rubygems.org). +For more information about publishing gems to RubyGems, see: [Creating and Publishing Your First Ruby Gem](http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html). + +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) +* Warnings, gotchas or tips that might help users and save them 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 included in the public API. + +Once your comments are good to go, navigate to your plugin directory and run: + +```bash +$ bin/rake rdoc +``` + +### References + +* [Developing a RubyGem using Bundler](https://github.com/radar/guides/blob/master/gem-development.md) +* [Using .gemspecs as Intended](http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/) +* [Gemspec Reference](http://docs.rubygems.org/read/chapter/20) +* [GemPlugins: A Brief Introduction to the Future of Rails Plugins](http://www.intridea.com/blog/2008/6/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins) |