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484 lines
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484 lines
13 KiB
Markdown
**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.**
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The Basics of Creating Rails Plugins
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====================================
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A Rails plugin is either an extension or a modification of the core framework. Plugins provide:
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* A way for developers to share bleeding-edge ideas without hurting the stable code base.
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* A segmented architecture so that units of code can be fixed or updated on their own release schedule.
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* An outlet for the core developers so that they don't have to include every cool new feature under the sun.
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After reading this guide, you will know:
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* How to create a plugin from scratch.
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* How to write and run tests for the plugin.
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This guide describes how to build a test-driven plugin that will:
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* Extend core Ruby classes like Hash and String.
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* Add methods to `ApplicationRecord` in the tradition of the `acts_as` plugins.
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* Give you information about where to put generators in your plugin.
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For the purpose of this guide pretend for a moment that you are an avid bird watcher.
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Your favorite bird is the Yaffle, and you want to create a plugin that allows other developers to share in the Yaffle
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goodness.
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--------------------------------------------------------------------------------
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Setup
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-----
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Currently, Rails plugins are built as gems, _gemified plugins_. They can be shared across
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different Rails applications using RubyGems and Bundler if desired.
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### Generate a gemified plugin.
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Rails ships with a `rails plugin new` command which creates a
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skeleton for developing any kind of Rails extension with the ability
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to run integration tests using a dummy Rails application. Create your
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plugin with the command:
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```bash
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$ rails plugin new yaffle
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```
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See usage and options by asking for help:
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```bash
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$ rails plugin new --help
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```
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Testing Your Newly Generated Plugin
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-----------------------------------
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You can navigate to the directory that contains the plugin, run the `bundle install` command
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and run the one generated test using the `bin/test` command.
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You should see:
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```bash
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1 runs, 1 assertions, 0 failures, 0 errors, 0 skips
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```
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This will tell you that everything got generated properly and you are ready to start adding functionality.
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Extending Core Classes
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----------------------
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This section will explain how to add a method to String that will be available anywhere in your Rails application.
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In this example you will add a method to String named `to_squawk`. To begin, create a new test file with a few assertions:
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```ruby
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# yaffle/test/core_ext_test.rb
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require "test_helper"
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class CoreExtTest < ActiveSupport::TestCase
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def test_to_squawk_prepends_the_word_squawk
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assert_equal "squawk! Hello World", "Hello World".to_squawk
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end
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end
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```
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Run `bin/test` to run the test. This test should fail because we haven't implemented the `to_squawk` method:
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```bash
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E
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Error:
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CoreExtTest#test_to_squawk_prepends_the_word_squawk:
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NoMethodError: undefined method `to_squawk' for "Hello World":String
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bin/test /path/to/yaffle/test/core_ext_test.rb:4
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.
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Finished in 0.003358s, 595.6483 runs/s, 297.8242 assertions/s.
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2 runs, 1 assertions, 0 failures, 1 errors, 0 skips
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```
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Great - now you are ready to start development.
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In `lib/yaffle.rb`, add `require "yaffle/core_ext"`:
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```ruby
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# yaffle/lib/yaffle.rb
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require "yaffle/railtie"
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require "yaffle/core_ext"
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module Yaffle
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# Your code goes here...
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end
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```
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Finally, create the `core_ext.rb` file and add the `to_squawk` method:
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```ruby
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# yaffle/lib/yaffle/core_ext.rb
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class String
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def to_squawk
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"squawk! #{self}".strip
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end
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end
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```
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To test that your method does what it says it does, run the unit tests with `bin/test` from your plugin directory.
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```bash
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2 runs, 2 assertions, 0 failures, 0 errors, 0 skips
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```
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To see this in action, change to the `test/dummy` directory, fire up a console, and start squawking:
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```bash
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$ bin/rails console
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>> "Hello World".to_squawk
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=> "squawk! Hello World"
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```
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Add an "acts_as" Method to Active Record
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----------------------------------------
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A common pattern in plugins is to add a method called `acts_as_something` to models. In this case, you
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want to write a method called `acts_as_yaffle` that adds a `squawk` method to your Active Record models.
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To begin, set up your files so that you have:
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```ruby
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# yaffle/test/acts_as_yaffle_test.rb
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require "test_helper"
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class ActsAsYaffleTest < ActiveSupport::TestCase
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end
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```
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```ruby
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# yaffle/lib/yaffle.rb
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require "yaffle/railtie"
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require "yaffle/core_ext"
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require "yaffle/acts_as_yaffle"
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module Yaffle
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# Your code goes here...
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end
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```
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```ruby
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# yaffle/lib/yaffle/acts_as_yaffle.rb
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module Yaffle
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module ActsAsYaffle
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end
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end
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```
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### Add a Class Method
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This plugin will expect that you've added a method to your model named `last_squawk`. However, the
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plugin users might have already defined a method on their model named `last_squawk` that they use
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for something else. This plugin will allow the name to be changed by adding a class method called `yaffle_text_field`.
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To start out, write a failing test that shows the behavior you'd like:
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```ruby
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# yaffle/test/acts_as_yaffle_test.rb
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require "test_helper"
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class ActsAsYaffleTest < ActiveSupport::TestCase
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def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
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assert_equal "last_squawk", Hickwall.yaffle_text_field
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end
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def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
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assert_equal "last_tweet", Wickwall.yaffle_text_field
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end
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end
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```
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When you run `bin/test`, you should see the following:
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```
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# Running:
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..E
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Error:
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ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
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NameError: uninitialized constant ActsAsYaffleTest::Wickwall
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bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8
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E
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Error:
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ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
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NameError: uninitialized constant ActsAsYaffleTest::Hickwall
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bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4
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Finished in 0.004812s, 831.2949 runs/s, 415.6475 assertions/s.
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4 runs, 2 assertions, 0 failures, 2 errors, 0 skips
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```
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This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test.
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We can easily generate these models in our "dummy" Rails application by running the following commands from the
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`test/dummy` directory:
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```bash
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$ cd test/dummy
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$ bin/rails generate model Hickwall last_squawk:string
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$ bin/rails generate model Wickwall last_squawk:string last_tweet:string
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```
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Now you can create the necessary database tables in your testing database by navigating to your dummy app
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and migrating the database. First, run:
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```bash
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$ cd test/dummy
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$ bin/rails db:migrate
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```
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While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act
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like yaffles.
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```ruby
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# test/dummy/app/models/hickwall.rb
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class Hickwall < ApplicationRecord
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acts_as_yaffle
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end
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# test/dummy/app/models/wickwall.rb
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class Wickwall < ApplicationRecord
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acts_as_yaffle yaffle_text_field: :last_tweet
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end
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```
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We will also add code to define the `acts_as_yaffle` method.
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```ruby
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# yaffle/lib/yaffle/acts_as_yaffle.rb
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module Yaffle
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module ActsAsYaffle
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extend ActiveSupport::Concern
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class_methods do
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def acts_as_yaffle(options = {})
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end
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end
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end
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end
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# test/dummy/app/models/application_record.rb
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class ApplicationRecord < ActiveRecord::Base
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include Yaffle::ActsAsYaffle
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self.abstract_class = true
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end
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```
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You can then return to the root directory (`cd ../..`) of your plugin and rerun the tests using `bin/test`.
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```
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# Running:
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.E
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Error:
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ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
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NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974ebbe9d8>
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bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4
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E
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Error:
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ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
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NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974eb8cfc8>
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bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8
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.
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Finished in 0.008263s, 484.0999 runs/s, 242.0500 assertions/s.
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4 runs, 2 assertions, 0 failures, 2 errors, 0 skips
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```
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Getting closer... Now we will implement the code of the `acts_as_yaffle` method to make the tests pass.
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```ruby
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# yaffle/lib/yaffle/acts_as_yaffle.rb
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module Yaffle
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module ActsAsYaffle
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extend ActiveSupport::Concern
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class_methods do
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def acts_as_yaffle(options = {})
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cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
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end
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end
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end
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end
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# test/dummy/app/models/application_record.rb
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class ApplicationRecord < ActiveRecord::Base
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include Yaffle::ActsAsYaffle
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self.abstract_class = true
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end
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```
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When you run `bin/test`, you should see the tests all pass:
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```bash
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4 runs, 4 assertions, 0 failures, 0 errors, 0 skips
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```
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### Add an Instance Method
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This plugin will add a method named 'squawk' to any Active Record object that calls `acts_as_yaffle`. The 'squawk'
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method will simply set the value of one of the fields in the database.
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To start out, write a failing test that shows the behavior you'd like:
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```ruby
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# yaffle/test/acts_as_yaffle_test.rb
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require "test_helper"
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class ActsAsYaffleTest < ActiveSupport::TestCase
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def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
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assert_equal "last_squawk", Hickwall.yaffle_text_field
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end
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def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
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assert_equal "last_tweet", Wickwall.yaffle_text_field
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end
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def test_hickwalls_squawk_should_populate_last_squawk
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hickwall = Hickwall.new
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hickwall.squawk("Hello World")
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assert_equal "squawk! Hello World", hickwall.last_squawk
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end
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def test_wickwalls_squawk_should_populate_last_tweet
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wickwall = Wickwall.new
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wickwall.squawk("Hello World")
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assert_equal "squawk! Hello World", wickwall.last_tweet
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end
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end
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```
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Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method `squawk'",
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then update `acts_as_yaffle.rb` to look like this:
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```ruby
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# yaffle/lib/yaffle/acts_as_yaffle.rb
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module Yaffle
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module ActsAsYaffle
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extend ActiveSupport::Concern
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included do
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def squawk(string)
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write_attribute(self.class.yaffle_text_field, string.to_squawk)
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end
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end
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class_methods do
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def acts_as_yaffle(options = {})
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cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
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end
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end
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end
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end
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# test/dummy/app/models/application_record.rb
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class ApplicationRecord < ActiveRecord::Base
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include Yaffle::ActsAsYaffle
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self.abstract_class = true
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end
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```
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Run `bin/test` one final time and you should see:
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```
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6 runs, 6 assertions, 0 failures, 0 errors, 0 skips
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```
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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:
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```ruby
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send("#{self.class.yaffle_text_field}=", string.to_squawk)
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```
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Generators
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----------
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Generators can be included in your gem simply by creating them in a `lib/generators` directory of your plugin. More information about
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the creation of generators can be found in the [Generators Guide](generators.html).
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Publishing Your Gem
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-------------------
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Gem plugins currently in development can easily be shared from any Git repository. To share the Yaffle gem with others, simply
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commit the code to a Git repository (like GitHub) and add a line to the `Gemfile` of the application in question:
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```ruby
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gem "yaffle", git: "https://github.com/rails/yaffle.git"
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```
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After running `bundle install`, your gem functionality will be available to the application.
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When the gem is ready to be shared as a formal release, it can be published to [RubyGems](https://rubygems.org).
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For more information about publishing gems to RubyGems, see: [Publishing your gem](http://guides.rubygems.org/publishing).
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RDoc Documentation
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------------------
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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.
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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:
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* Your name
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* How to install
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* How to add the functionality to the app (several examples of common use cases)
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* Warnings, gotchas or tips that might help users and save them time
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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.
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Once your comments are good to go, navigate to your plugin directory and run:
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```bash
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$ bundle exec rake rdoc
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```
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### References
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* [Developing a RubyGem using Bundler](https://github.com/radar/guides/blob/master/gem-development.md)
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* [Using .gemspecs as Intended](http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/)
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* [Gemspec Reference](http://guides.rubygems.org/specification-reference/)
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