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diff --git a/railties/guides/source/engines.textile b/railties/guides/source/engines.textile deleted file mode 100644 index 126d09ab87..0000000000 --- a/railties/guides/source/engines.textile +++ /dev/null @@ -1,393 +0,0 @@ -h2. Getting Started with Engines - -In this guide you will learn about engines and how they can be used to provide additional functionality to their host applications through a clean and very easy-to-use interface. You will learn the following things in this guide: - -* What makes an engine -* How to generate an engine -* Building features for the engine -* Hooking the engine into an application -* Overriding engine functionality in the application - -endprologue. - -h3. What are engines? - -Engines can be considered miniature applications that provide functionality to their host applications. A Rails application is actually just a "supercharged" engine, with the +Rails::Application+ class inheriting from +Rails::Engine+. Therefore, engines and applications share common functionality but are at the same time two separate beasts. Engines and applications also share a common structure, as you'll see throughout this guide. - -Engines are also closely related to plugins where the two share a common +lib+ directory structure and are both generated using the +rails plugin new+ generator. - -The engine that will be generated for this guide will be called "blorgh". The engine will provide blogging functionality to its host applications, allowing for new posts and comments to be created. For now, you will be working solely within the engine itself and in later sections you'll see how to hook it into an application. - -Engines can also be isolated from their host applications. This means that an application is able to have a path provided by a routing helper such as +posts_path+ and use an engine also that provides a path also called +posts_path+, and the two would not clash. Along with this, controllers, models and table names are also namespaced. You'll see how to do this later in this guide. - -To see demonstrations of other engines, check out "Devise":https://github.com/plataformatec/devise, an engine that provides authentication for its parent applications, or "Forem":https://github.com/radar/forem, an engine that provides forum functionality. - -Finally, engines would not have be possible without the work of James Adam, Piotr Sarnacki, the Rails Core Team, and a number of other people. If you ever meet them, don't forget to say thanks! - -h3. Generating an engine - -To generate an engine with Rails 3.1, you will need to run the plugin generator and pass it the +--mountable+ option. To generate the beginnings of the "blorgh" engine you will need to run this command in a terminal: - -<shell> -$ rails plugin new blorgh --mountable -</shell> - -The +--mountable+ option tells the plugin generator that you want to create an engine (which is a mountable plugin, hence the option name), creating the basic directory structure of an engine by providing things such as the foundations of an +app+ folder, as well a +config/routes.rb+ file. This generator also provides a file at +lib/blorgh/engine.rb+ which is identical in function to an application's +config/application.rb+ file. - -h4. Inside an engine - -h5. Critical files - -At the root of the engine's directory, lives a +blorgh.gemspec+ file. When you include the engine into the application later on, you will do so with this line in a Rails application's +Gemfile+: - -<ruby> - gem 'blorgh', :path => "vendor/engines/blorgh" -</ruby> - -By specifying it as a gem within the +Gemfile+, Bundler will load it as such, parsing this +blorgh.gemspec+ file and requiring a file within the +lib+ directory called +lib/blorgh.rb+. This file requires the +blorgh/engine.rb+ file (located at +lib/blorgh/engine.rb+) and defines a base module called +Blorgh+. - -<ruby> -require "blorgh/engine" - -module Blorgh -end -</ruby> - -Within +lib/blorgh/engine.rb+ is the base class for the engine: - -<ruby> -module Blorgh - class Engine < Rails::Engine - isolate_namespace Blorgh - end -end -</ruby> - -By inheriting from the +Rails::Engine+ class, this engine gains all the functionality it needs, such as being able to serve requests to its controllers. - -The +isolate_namespace+ method here deserves special notice. This call is responsible for isolating the controllers, models, routes and other things into their own namespace. Without this, there is a possibility that the engine's components could "leak" into the application, causing unwanted disruption. It is recommended that this line be left within this file. - -h5. +app+ directory - -Inside the +app+ directory there lives the standard +assets+, +controllers+, +helpers+, +mailers+, +models+ and +views+ directories that you should be familiar with from an application. The +helpers+, +mailers+ and +models+ directories are empty and so aren't described in this section. We'll look more into models in a future section. - -Within the +app/assets+ directory, there is the +images+, +javascripts+ and +stylesheets+ directories which, again, you should be familiar with due to their similarities of an application. One difference here however is that each directory contains a sub-directory with the engine name. Because this engine is going to be namespaced, its assets should be too. - -Within the +app/controllers+ directory there is a +blorgh+ directory and inside that a file called +application_controller.rb+. This file will provide any common functionality for the controllers of the engine. The +blorgh+ directory is where the other controllers for the engine will go. By placing them within this namespaced directory, you prevent them from possibly clashing with identically-named controllers within other engines or even within the application. - -Lastly, the +app/views+ directory contains a +layouts+ folder which contains file at +blorgh/application.html.erb+ which allows you to specify a layout for the engine. If this engine is to be used as a stand-alone engine, then you would add any customization to its layout in this file, rather than the applications +app/views/layouts/application.html.erb+ file. - -h5. +script+ directory - -This directory contains one file, +script/rails+, which allows you to use the +rails+ sub-commands and generators just like you would within an application. This means that you will very easily be able to generate new controllers and models for this engine. - -h5. +test+ directory - -The +test+ directory is where tests for the engine will go. To test the engine, there is a cut-down version of a Rails application embedded within it at +test/dummy+. This application will mount the engine in the +test/dummy/config/routes.rb+ file: - -<ruby> -Rails.application.routes.draw do - - mount Blorgh::Engine => "/blorgh" -end -</ruby> - -This line mounts the engine at the path of +/blorgh+, which will make it accessible through the application only at that path. We will look more into mounting an engine after some features have been developed. - -Also in the test directory is the +test/integration+ directory, where integration tests for the engine should be placed. - -h3. Providing engine functionality - -The engine that this guide covers will provide posting and commenting functionality. - -h4. Generating a post resource - -The first thing to generate for a blog engine is the +Post+ model and related controller. To quickly generate this, you can use the Rails scaffold generator. - -<shell> -$ rails generate scaffold post title:string text:text -</shell> - -This command will output this information: - -<shell> -invoke active_record -create db/migrate/[timestamp]_create_blorgh_posts.rb -create app/models/blorgh/post.rb -invoke test_unit -create test/unit/blorgh/post_test.rb -create test/fixtures/blorgh/posts.yml - route resources :posts -invoke scaffold_controller -create app/controllers/blorgh/posts_controller.rb -invoke erb -create app/views/blorgh/posts -create app/views/blorgh/posts/index.html.erb -create app/views/blorgh/posts/edit.html.erb -create app/views/blorgh/posts/show.html.erb -create app/views/blorgh/posts/new.html.erb -create app/views/blorgh/posts/_form.html.erb -invoke test_unit -create test/functional/blorgh/posts_controller_test.rb -invoke helper -create app/helpers/blorgh/posts_helper.rb -invoke test_unit -create test/unit/helpers/blorgh/posts_helper_test.rb -invoke assets -invoke js -create app/assets/javascripts/blorgh/posts.js -invoke css -create app/assets/stylesheets/blorgh/posts.css -invoke css -create app/assets/stylesheets/scaffold.css -</shell> - -The first thing that the scaffold generator does is invoke the +active_record+ generator, which generates a migration and a model for the resource. Note here, however, that the migration is called +create_blorgh_posts+ rather than the usual +create_posts+. This is due to the +isolate_namespace+ method called in the +Blorgh::Engine+ class's definition. The model here is also namespaced, being placed at +app/models/blorgh/post.rb+ rather than +app/models/post.rb+. - -Next, the +test_unit+ generator is invoked for this model, generating a unit test at +test/unit/blorgh/post_test.rb+ (rather than +test/unit/post_test.rb+) and a fixture at +test/fixtures/blorgh/posts.yml+ (rather than +test/fixtures/posts.yml+). - -After that, a line for the resource is inserted into the +config/routes.rb+ file for the engine. This line is simply +resources :posts+, turning the +config/routes.rb+ file into this: - -<ruby> -Blorgh::Engine.routes.draw do - resources :posts - -end -</ruby> - -Note here that the routes are drawn upon the +Blorgh::Engine+ object rather than the +YourApp::Application+ class. This is so that the engine routes are confined to the engine itself and can be mounted at a specific point as shown in the "test directory":#test-directory section. - -Next, the +scaffold_controller+ generator is invoked, generating a controlled called +Blorgh::PostsController+ (at +app/controllers/blorgh/posts_controller.rb+) and its related views at +app/views/blorgh/posts+. This generator also generates a functional test for the controller (+test/functional/blorgh/posts_controller_test.rb+) and a helper (+app/helpers/blorgh/posts_controller.rb+). - -Everything this generator has generated is neatly namespaced. The controller's class is defined within the +Blorgh+ module: - -<ruby> -module Blorgh - class PostsController < ApplicationController - ... - end -end -</ruby> - -NOTE: The +ApplicationController+ class being inherited from here is the +Blorgh::ApplicationController+, not an application's +ApplicationController+. - -The helper is also namespaced: - -<ruby> -module Blorgh - class PostsHelper - ... - end -end -</ruby> - -This helps prevent conflicts with any other engine or application that may have a post resource also. - -Finally, two files that are the assets for this resource are generated, +app/assets/javascripts/blorgh/posts.js+ and +app/assets/javascripts/blorgh/posts.css+. You'll see how to use these a little later. - -By default, the scaffold styling is not applied to the engine as the engine's layout file, +app/views/blorgh/application.html.erb+ doesn't load it. To make this apply, insert this line into the +<head>+ tag of this layout: - -<erb> -<%= stylesheet_link_tag "scaffold" %> -</erb> - -You can see what the engine has so far by running +rake db:migrate+ at the root of our engine to run the migration generated by the scaffold generator, and then running +rails server+. When you open +http://localhost:3000/blorgh/posts+ you will see the default scaffold that has been generated. - -!images/engines_scaffold.png(Blank engine scaffold)! - -Click around! You've just generated your first engine's first functions. - -If you'd rather play around in the console, +rails console+ will also work just like a Rails application. Remember: the +Post+ model is namespaced, so to reference it you must call it as +Blorgh::Post+. - -<ruby> - >> Blorgh::Post.find(1) - => #<Blorgh::Post id: 1 ...> -</ruby> - -One final thing is that the +posts+ resource for this engine should be the root of the engine. Whenever someone goes to the root path where the engine is mounted, they should be shown a list of posts. This can be made to happen if this line is inserted into the +config/routes.rb+ file inside the engine: - -<ruby> -root :to => "posts#index" -</ruby> - -Now people will only need to go to the root of the engine to see all the posts, rather than visiting +/posts+. - -h4. Generating a comments resource - -Now that the engine has the ability to create new blog posts, it only makes sense to add commenting functionality as well. To do get this, you'll need to generate a comment model, a comment controller and then modify the posts scaffold to display comments and allow people to create new ones. - -Run the model generator and tell it to generate a +Comment+ model, with the related table having two columns: a +post_id+ integer and +text+ text column. - -<shell> -$ rails generate model Comment post_id:integer text:text -</shell> - -This will output the following: - -<shell> -invoke active_record -create db/migrate/[timestamp]_create_blorgh_comments.rb -create app/models/blorgh/comment.rb -invoke test_unit -create test/unit/blorgh/comment_test.rb -create test/fixtures/blorgh/comments.yml -</shell> - -This generator call will generate just the necessary model files it needs, namespacing the files under a +blorgh+ directory and creating a model class called +Blorgh::Comment+. - -To show the comments on a post, edit +app/views/posts/show.html.erb+ and add this line before the "Edit" link: - -<erb> -<h3>Comments</h3> -<%= render @post.comments %> -</erb> - -This line will require there to be a +has_many+ association for comments defined on the +Blorgh::Post+ model, which there isn't right now. To define one, open +app/models/blorgh/post.rb+ and add this line into the model: - -<ruby> -has_many :comments -</ruby> - -Turning the model into this: - -<ruby> -module Blorgh - class Post < ActiveRecord::Base - has_many :comments - end -end -</ruby> - -Because the +has_many+ is defined inside a class that is inside the +Blorgh+ module, Rails will know that you want to use the +Blorgh::Comment+ model for these objects. - -Next, there needs to be a form so that comments can be created on a post. To add this, put this line underneath the call to +render @post.comments+ in +app/views/blorgh/posts/show.html.erb+: - -<erb> -<%= render "blorgh/comments/form" %> -</erb> - -Next, the partial that this line will render needs to exist. Create a new directory at +app/views/blorgh/comments+ and in it a new file called +_form.html.erb+ which has this content to create the required partial: - -<erb> -<h3>New comment</h3> -<%= form_for [@post, @post.comments.build] do |f| %> - <p> - <%= f.label :text %><br /> - <%= f.text_area :text %> - </p> - <%= f.submit %> -<% end %> -</erb> - -This form, when submitted, is going to attempt to post to a route of +posts/:post_id/comments+ within the engine. This route doesn't exist at the moment, but can be created by changing the +resources :posts+ line inside +config/routes.rb+ into these lines: - -<ruby> -resources :posts do - resources :comments -end -</ruby> - -The route now will exist, but the controller that this route goes to does not. To create it, run this command: - -<shell> -$ rails g controller comments -</shell> - -This will generate the following things: - -<shell> -create app/controllers/blorgh/comments_controller.rb -invoke erb - exist app/views/blorgh/comments -invoke test_unit -create test/functional/blorgh/comments_controller_test.rb -invoke helper -create app/helpers/blorgh/comments_helper.rb -invoke test_unit -create test/unit/helpers/blorgh/comments_helper_test.rb -invoke assets -invoke js -create app/assets/javascripts/blorgh/comments.js -invoke css -create app/assets/stylesheets/blorgh/comments.css -</shell> - -The form will be making a +POST+ request to +/posts/:post_id/comments+, which will correspond with the +create+ action in +Blorgh::CommentsController+. This action needs to be created and can be done by putting the following lines inside the class definition in +app/controllers/blorgh/comments_controller.rb+: - -<ruby> -def create - @post = Post.find(params[:post_id]) - @comment = @post.comments.build(params[:comment]) - flash[:notice] = "Comment has been created!" - redirect_to post_path -end -</ruby> - -This is the final part required to get the new comment form working. Displaying the comments however, is not quite right yet. If you were to create a comment right now you would see this error: - -<text> - Missing partial blorgh/comments/comment with {:handlers=>[:erb, :builder], :formats=>[:html], :locale=>[:en, :en]}. Searched in: - * "/Users/ryan/Sites/side_projects/blorgh/test/dummy/app/views" - * "/Users/ryan/Sites/side_projects/blorgh/app/views" -</text> - -The engine is unable to find the partial required for rendering the comments. Rails has looked firstly in the application's (+test/dummy+) +app/views+ directory and then in the engine's +app/views+ directory. When it can't find it, it will throw this error. The engine knows to look for +blorgh/comments/comment+ because the model object it is receiving is from the +Blorgh::Comment+ class. - -This partial will be responsible for rendering just the comment text, for now. Create a new file at +app/views/blorgh/comments/_comment.html.erb+ and put this line inside it: - -<erb> -<%= comment_counter + 1 %>. <%= comment.text %> -</erb> - -The +comment_counter+ local variable is given to us by the +<%= render @post.comments %>+ call, as it will define this automatically and increment the counter as it iterates through each comment. It's used in this example to display a small number next to each comment when it's created. - -That completes the comment function of the blogging engine. Now it's time to use it within an application. - -h3. Hooking into application - -Using an engine within an application is very easy. First, the engine needs to be specified inside the application's +Gemfile+. If there isn't an application handy to test this out in, generate one using the +rails new+ command outside of the engine directory like this: - -<shell> -$ rails new unicorn -</shell> - -Usually, specifying the engine inside the Gemfile would be done by specifying it as a normal, everyday gem. - -<ruby> -gem 'devise' -</ruby> - -Because the +blorgh+ engine is still under development, it will need to have a +:path+ option for its +Gemfile+ specification: - -<ruby> -gem 'blorgh', :path => "/path/to/blorgh" -</ruby> - -If the whole +blorgh+ engine directory is copied to +vendor/engines/blorgh+ then it could be specified in the +Gemfile+ like this: - -<ruby> -gem 'blorgh', :path => "vendor/engines/blorgh" -</ruby> - -As described earlier, by placing the gem in the +Gemfile+ it will be loaded when Rails is loaded, as it will first require +lib/blorgh.rb+ in the engine and then +lib/blorgh/engine.rb+, which is the file that defines the major pieces of functionality for the engine. - -To make the engine's functionality accessible from within an application, it needs to be mounted in that application's +config/routes.rb+ file: - -<ruby> - mount Blorgh::Engine, :at => "blog" -</ruby> - -NOTE: Other engines, such as Devise, handle this a little differently by making you specify custom helpers such as +devise_for+ in the routes. These helpers do exactly the same thing, mounting pieces of the engines's functionality at a pre-defined path which may be customizable. - - - -This line will mount the engine -TODO: Application will provide a User foundation class which the engine hooks into through a configuration setting, configurable in the application's initializers. The engine will be mounted at the +/blog+ path in the application. - -h3. Overriding engine functionality - -TODO: Cover how to override engine functionality in the engine, such as controllers and views. - -IDEA: I like Devise's +devise :controllers => { "sessions" => "sessions" }+ idea. Perhaps we could incorporate that into the guide? -TODO: Mention how to use assets within an engine? -TODO: Mention how to depend on external gems, like RedCarpet. |