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diff --git a/guides/source/plugins.textile b/guides/source/plugins.textile new file mode 100644 index 0000000000..97b4eca779 --- /dev/null +++ b/guides/source/plugins.textile @@ -0,0 +1,432 @@ +h2. 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 should be familiar with: + +* Creating a plugin from scratch +* Writing and running 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. + +endprologue. + +h3. Setup + +Before you continue, take a moment to decide if your new plugin will be potentially shared across different Rails applications. + +* If your plugin is specific to your application, your new plugin will be a _vendored plugin_. +* If you think your plugin may be used across applications, build it as a _gemified plugin_. + +h4. Generate a gemified plugin. + +Writing your Rails plugin as a gem, rather than as a vendored plugin, + lets you share your plugin across different rails applications using + RubyGems and Bundler. + +Rails 3.1 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. See usage + and options by asking for help: + +<shell> +$ rails plugin --help +</shell> + +h3. 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: + +<shell> + 2 tests, 2 assertions, 0 failures, 0 errors, 0 skips +</shell> + +This will tell you that everything got generated properly and you are ready to start adding functionality. + +h3. 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 < Test::Unit::TestCase + def test_to_squawk_prepends_the_word_squawk + assert_equal "squawk! Hello World", "Hello World".to_squawk + end +end +</ruby> + +Run +rake+ to run the test. This test should fail because we haven't implemented the +to_squawk+ method: + +<shell> + 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' +</shell> + +Great - now you are ready to start development. + +Then in +lib/yaffle.rb+ require +lib/core_ext+: + +<ruby> +# yaffle/lib/yaffle.rb + +require "yaffle/core_ext" + +module Yaffle +end +</ruby> + +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 +</ruby> + +To test that your method does what it says it does, run the unit tests with +rake+ from your plugin directory. + +<shell> + 3 tests, 3 assertions, 0 failures, 0 errors, 0 skips +</shell> + +To see this in action, change to the test/dummy directory, fire up a console and start squawking: + +<shell> +$ rails console +>> "Hello World".to_squawk +=> "squawk! Hello World" +</shell> + +h3. 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 < Test::Unit::TestCase +end +</ruby> + +<ruby> +# yaffle/lib/yaffle.rb + +require "yaffle/core_ext" +require 'yaffle/acts_as_yaffle' + +module Yaffle +end +</ruby> + +<ruby> +# yaffle/lib/yaffle/acts_as_yaffle.rb + +module Yaffle + module ActsAsYaffle + # your code will go here + end +end +</ruby> + +h4. 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 < 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_wickwalls_yaffle_text_field_should_be_last_tweet + assert_equal :last_tweet, Wickwall.yaffle_text_field + end + +end +</ruby> + +When you run +rake+, you should see the following: + +<shell> + 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 +</shell> + +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: + +<shell> +$ cd test/dummy +$ rails generate model Hickwall last_squawk:string +$ rails generate model Wickwall last_squawk:string last_tweet:string +</shell> + +Now you can create the necessary database tables in your testing database by navigating to your dummy app +and migrating the database. First + +<shell> +$ cd test/dummy +$ rake db:migrate +$ rake db:test:prepare +</shell> + +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 + +</ruby> + +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 +</ruby> + +You can then return to the root directory (+cd ../..+) of your plugin and rerun the tests using +rake+. + +<shell> + 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 + +</shell> + +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 +</ruby> + +When you run +rake+ you should see the tests all pass: + +<shell> + 5 tests, 5 assertions, 0 failures, 0 errors, 0 skips +</shell> + +h4. 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 < 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_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 +</ruby> + +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 +</ruby> + +Run +rake+ one final time and you should see: + +<shell> + 7 tests, 7 assertions, 0 failures, 0 errors, 0 skips +</shell> + +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 <tt>send("#{self.class.yaffle_text_field}=", string.to_squawk)</tt>. + +h3. 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 + +h3. 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' +</ruby> + +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: "http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html":http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html + +h3. 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: + +<shell> +$ rake rdoc +</shell> + +h4. 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":http://www.mbleigh.com/2008/06/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins |