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<h2>The Basics of Creating Rails Plugins</h2><p>A Rails plugin is either an extension or a modification of the core framework. Plugins provide:</p>
<ul>
<li>A way for developers to share bleeding-edge ideas without hurting the stable code base.</li>
<li>A segmented architecture so that units of code can be fixed or updated on their own release schedule.</li>
<li>An outlet for the core developers so that they don't have to include every cool new feature under the sun.</li>
</ul>
<p>After reading this guide, you will know:</p>
<ul>
<li>How to create a plugin from scratch.</li>
<li>How to write and run tests for the plugin.</li>
</ul>
<p>This guide describes how to build a test-driven plugin that will:</p>
<ul>
<li>Extend core Ruby classes like Hash and String.</li>
<li>Add methods to <code>ApplicationRecord</code> in the tradition of the <code>acts_as</code> plugins.</li>
<li>Give you information about where to put generators in your plugin.</li>
</ul>
<p>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.</p>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#setup">Setup</a>
<ul>
<li><a href="#generate-a-gemified-plugin">Generate a gemified plugin.</a></li>
</ul>
</li>
<li><a href="#testing-your-newly-generated-plugin">Testing Your Newly Generated Plugin</a></li>
<li><a href="#extending-core-classes">Extending Core Classes</a></li>
<li>
<a href="#add-an-acts-as-method-to-active-record">Add an "acts_as" Method to Active Record</a>
<ul>
<li><a href="#add-a-class-method">Add a Class Method</a></li>
<li><a href="#add-an-instance-method">Add an Instance Method</a></li>
</ul>
</li>
<li><a href="#generators">Generators</a></li>
<li><a href="#publishing-your-gem">Publishing Your Gem</a></li>
<li>
<a href="#rdoc-documentation">RDoc Documentation</a>
<ul>
<li><a href="#references">References</a></li>
</ul>
</li>
</ol>
</div>
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<div id="container">
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<div id="mainCol">
<h3 id="setup"><a class="anchorlink" href="#setup">1 Setup</a></h3><p>Currently, Rails plugins are built as gems, <em>gemified plugins</em>. They can be shared across
different Rails applications using RubyGems and Bundler if desired.</p><h4 id="generate-a-gemified-plugin"><a class="anchorlink" href="#generate-a-gemified-plugin">1.1 Generate a gemified plugin.</a></h4><p>Rails ships with a <code>rails plugin new</code> 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:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ rails plugin new yaffle
</pre>
</div>
<p>See usage and options by asking for help:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ rails plugin new --help
</pre>
</div>
<h3 id="testing-your-newly-generated-plugin"><a class="anchorlink" href="#testing-your-newly-generated-plugin">2 Testing Your Newly Generated Plugin</a></h3><p>You can navigate to the directory that contains the plugin, run the <code>bundle install</code> command
and run the one generated test using the <code>bin/test</code> command.</p><p>You should see:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
1 runs, 1 assertions, 0 failures, 0 errors, 0 skips
</pre>
</div>
<p>This will tell you that everything got generated properly and you are ready to start adding functionality.</p><h3 id="extending-core-classes"><a class="anchorlink" href="#extending-core-classes">3 Extending Core Classes</a></h3><p>This section will explain how to add a method to String that will be available anywhere in your Rails application.</p><p>In this example you will add a method to String named <code>to_squawk</code>. To begin, create a new test file with a few assertions:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<p>Run <code>bin/test</code> to run the test. This test should fail because we haven't implemented the <code>to_squawk</code> method:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
E
Error:
CoreExtTest#test_to_squawk_prepends_the_word_squawk:
NoMethodError: undefined method `to_squawk' for "Hello World":String
bin/test /path/to/yaffle/test/core_ext_test.rb:4
.
Finished in 0.003358s, 595.6483 runs/s, 297.8242 assertions/s.
2 runs, 1 assertions, 0 failures, 1 errors, 0 skips
</pre>
</div>
<p>Great - now you are ready to start development.</p><p>In <code>lib/yaffle.rb</code>, add <code>require "yaffle/core_ext"</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle.rb
require "yaffle/railtie"
require "yaffle/core_ext"
module Yaffle
# Your code goes here...
end
</pre>
</div>
<p>Finally, create the <code>core_ext.rb</code> file and add the <code>to_squawk</code> method:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle/core_ext.rb
class String
def to_squawk
"squawk! #{self}".strip
end
end
</pre>
</div>
<p>To test that your method does what it says it does, run the unit tests with <code>bin/test</code> from your plugin directory.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
2 runs, 2 assertions, 0 failures, 0 errors, 0 skips
</pre>
</div>
<p>To see this in action, change to the <code>test/dummy</code> directory, fire up a console, and start squawking:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ rails console
>> "Hello World".to_squawk
=> "squawk! Hello World"
</pre>
</div>
<h3 id="add-an-acts-as-method-to-active-record"><a class="anchorlink" href="#add-an-acts-as-method-to-active-record">4 Add an "acts_as" Method to Active Record</a></h3><p>A common pattern in plugins is to add a method called <code>acts_as_something</code> to models. In this case, you
want to write a method called <code>acts_as_yaffle</code> that adds a <code>squawk</code> method to your Active Record models.</p><p>To begin, set up your files so that you have:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/test/acts_as_yaffle_test.rb
require "test_helper"
class ActsAsYaffleTest < ActiveSupport::TestCase
end
</pre>
</div>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle.rb
require "yaffle/railtie"
require "yaffle/core_ext"
require "yaffle/acts_as_yaffle"
module Yaffle
# Your code goes here...
end
</pre>
</div>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle
module ActsAsYaffle
end
end
</pre>
</div>
<h4 id="add-a-class-method"><a class="anchorlink" href="#add-a-class-method">4.1 Add a Class Method</a></h4><p>This plugin will expect that you've added a method to your model named <code>last_squawk</code>. However, the
plugin users might have already defined a method on their model named <code>last_squawk</code> that they use
for something else. This plugin will allow the name to be changed by adding a class method called <code>yaffle_text_field</code>.</p><p>To start out, write a failing test that shows the behavior you'd like:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<p>When you run <code>bin/test</code>, you should see the following:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
# Running:
..E
Error:
ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
NameError: uninitialized constant ActsAsYaffleTest::Wickwall
bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8
E
Error:
ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
NameError: uninitialized constant ActsAsYaffleTest::Hickwall
bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4
Finished in 0.004812s, 831.2949 runs/s, 415.6475 assertions/s.
4 runs, 2 assertions, 0 failures, 2 errors, 0 skips
</pre>
</div>
<p>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
<code>test/dummy</code> directory:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ cd test/dummy
$ rails generate model Hickwall last_squawk:string
$ rails generate model Wickwall last_squawk:string last_tweet:string
</pre>
</div>
<p>Now you can create the necessary database tables in your testing database by navigating to your dummy app
and migrating the database. First, run:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ cd test/dummy
$ rails db:migrate
</pre>
</div>
<p>While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act
like yaffles.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# test/dummy/app/models/hickwall.rb
class Hickwall < ApplicationRecord
acts_as_yaffle
end
# test/dummy/app/models/wickwall.rb
class Wickwall < ApplicationRecord
acts_as_yaffle yaffle_text_field: :last_tweet
end
</pre>
</div>
<p>We will also add code to define the <code>acts_as_yaffle</code> method.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern
class_methods do
def acts_as_yaffle(options = {})
end
end
end
end
# test/dummy/app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle
self.abstract_class = true
end
</pre>
</div>
<p>You can then return to the root directory (<code>cd ../..</code>) of your plugin and rerun the tests using <code>bin/test</code>.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
# Running:
.E
Error:
ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974ebbe9d8>
bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4
E
Error:
ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974eb8cfc8>
bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8
.
Finished in 0.008263s, 484.0999 runs/s, 242.0500 assertions/s.
4 runs, 2 assertions, 0 failures, 2 errors, 0 skips
</pre>
</div>
<p>Getting closer... Now we will implement the code of the <code>acts_as_yaffle</code> method to make the tests pass.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern
class_methods do
def acts_as_yaffle(options = {})
cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
end
end
end
end
# test/dummy/app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle
self.abstract_class = true
end
</pre>
</div>
<p>When you run <code>bin/test</code>, you should see the tests all pass:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
4 runs, 4 assertions, 0 failures, 0 errors, 0 skips
</pre>
</div>
<h4 id="add-an-instance-method"><a class="anchorlink" href="#add-an-instance-method">4.2 Add an Instance Method</a></h4><p>This plugin will add a method named 'squawk' to any Active Record object that calls <code>acts_as_yaffle</code>. The 'squawk'
method will simply set the value of one of the fields in the database.</p><p>To start out, write a failing test that shows the behavior you'd like:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<p>Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method <code>squawk'",
then update</code>acts_as_yaffle.rb` to look like this:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern
included do
def squawk(string)
write_attribute(self.class.yaffle_text_field, string.to_squawk)
end
end
class_methods do
def acts_as_yaffle(options = {})
cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
end
end
end
end
# test/dummy/app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle
self.abstract_class = true
end
</pre>
</div>
<p>Run <code>bin/test</code> one final time and you should see:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
6 runs, 6 assertions, 0 failures, 0 errors, 0 skips
</pre>
</div>
<div class="note"><p>The use of <code>write_attribute</code> 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:</p></div><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
send("#{self.class.yaffle_text_field}=", string.to_squawk)
</pre>
</div>
<h3 id="generators"><a class="anchorlink" href="#generators">5 Generators</a></h3><p>Generators can be included in your gem simply by creating them in a <code>lib/generators</code> directory of your plugin. More information about
the creation of generators can be found in the <a href="generators.html">Generators Guide</a>.</p><h3 id="publishing-your-gem"><a class="anchorlink" href="#publishing-your-gem">6 Publishing Your Gem</a></h3><p>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 <code>Gemfile</code> of the application in question:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
gem "yaffle", git: "https://github.com/rails/yaffle.git"
</pre>
</div>
<p>After running <code>bundle install</code>, your gem functionality will be available to the application.</p><p>When the gem is ready to be shared as a formal release, it can be published to <a href="https://rubygems.org">RubyGems</a>.
For more information about publishing gems to RubyGems, see: <a href="https://guides.rubygems.org/publishing">Publishing your gem</a>.</p><h3 id="rdoc-documentation"><a class="anchorlink" href="#rdoc-documentation">7 RDoc Documentation</a></h3><p>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.</p><p>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:</p>
<ul>
<li>Your name</li>
<li>How to install</li>
<li>How to add the functionality to the app (several examples of common use cases)</li>
<li>Warnings, gotchas or tips that might help users and save them time</li>
</ul>
<p>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 <code>#:nodoc:</code> comments to those parts of the code that are not included in the public API.</p><p>Once your comments are good to go, navigate to your plugin directory and run:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ bundle exec rake rdoc
</pre>
</div>
<h4 id="references"><a class="anchorlink" href="#references">7.1 References</a></h4>
<ul>
<li><a href="https://github.com/radar/guides/blob/master/gem-development.md">Developing a RubyGem using Bundler</a></li>
<li><a href="http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/">Using .gemspecs as Intended</a></li>
<li><a href="https://guides.rubygems.org/specification-reference/">Gemspec Reference</a></li>
</ul>
<h3>Feedback</h3>
<p>
You're encouraged to help improve the quality of this guide.
</p>
<p>
Please contribute if you see any typos or factual errors.
To get started, you can read our <a href="https://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#contributing-to-the-rails-documentation">documentation contributions</a> section.
</p>
<p>
You may also find incomplete content or stuff that is not up to date.
Please do add any missing documentation for master. Make sure to check
<a href="https://edgeguides.rubyonrails.org">Edge Guides</a> first to verify
if the issues are already fixed or not on the master branch.
Check the <a href="ruby_on_rails_guides_guidelines.html">Ruby on Rails Guides Guidelines</a>
for style and conventions.
</p>
<p>
If for whatever reason you spot something to fix but cannot patch it yourself, please
<a href="https://github.com/rails/rails/issues">open an issue</a>.
</p>
<p>And last but not least, any kind of discussion regarding Ruby on Rails
documentation is very welcome on the <a href="https://groups.google.com/forum/#!forum/rubyonrails-docs">rubyonrails-docs mailing list</a>.
</p>
</div>
</div>
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