diff options
Diffstat (limited to 'guides/source/engines.md')
| -rw-r--r-- | guides/source/engines.md | 189 |
1 files changed, 154 insertions, 35 deletions
diff --git a/guides/source/engines.md b/guides/source/engines.md index 180a786237..1e93a19c84 100644 --- a/guides/source/engines.md +++ b/guides/source/engines.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Getting Started with Engines ============================ @@ -14,6 +14,7 @@ After reading this guide, you will know: * How to build features for the engine. * How to hook the engine into an application. * How to override engine functionality in the application. +* Avoid loading Rails frameworks with Load and Configuration Hooks -------------------------------------------------------------------------------- @@ -62,7 +63,7 @@ authentication for its parent applications, or [Thredded](https://github.com/thredded/thredded), an engine that provides forum functionality. There's also [Spree](https://github.com/spree/spree) which provides an e-commerce platform, and -[RefineryCMS](https://github.com/refinery/refinerycms), a CMS engine. +[Refinery CMS](https://github.com/refinery/refinerycms), a CMS engine. Finally, engines would not have been possible without the work of James Adam, Piotr Sarnacki, the Rails Core Team, and a number of other people. If you ever @@ -187,7 +188,7 @@ inside the application, performing tasks such as adding the `app` directory of the engine to the load path for models, mailers, controllers, and views. The `isolate_namespace` method here deserves special notice. This call is -responsible for isolating the controllers, models, routes and other things into +responsible for isolating the controllers, models, routes, and other things into their own namespace, away from similar components inside the application. Without this, there is a possibility that the engine's components could "leak" into the application, causing unwanted disruption, or that important engine @@ -201,7 +202,7 @@ within the `Engine` class definition. Without it, classes generated in an engine **may** conflict with an application. What this isolation of the namespace means is that a model generated by a call -to `bin/rails g model`, such as `bin/rails g model article`, won't be called `Article`, but +to `rails g model`, such as `rails g model article`, won't be called `Article`, but instead be namespaced and called `Blorgh::Article`. In addition, the table for the model is namespaced, becoming `blorgh_articles`, rather than simply `articles`. Similar to the model namespacing, a controller called `ArticlesController` becomes @@ -312,13 +313,16 @@ The engine that this guide covers provides submitting articles and commenting functionality and follows a similar thread to the [Getting Started Guide](getting_started.html), with some new twists. +NOTE: For this section, make sure to run the commands in the root of the +`blorgh` engine's directory. + ### Generating an Article Resource The first thing to generate for a blog engine is the `Article` model and related controller. To quickly generate this, you can use the Rails scaffold generator. ```bash -$ bin/rails generate scaffold article title:string text:text +$ rails generate scaffold article title:string text:text ``` This command will output this information: @@ -345,6 +349,9 @@ invoke test_unit create test/controllers/blorgh/articles_controller_test.rb invoke helper create app/helpers/blorgh/articles_helper.rb +invoke test_unit +create test/application_system_test_case.rb +create test/system/articles_test.rb invoke assets invoke js create app/assets/javascripts/blorgh/articles.js @@ -423,7 +430,7 @@ Finally, the assets for this resource are generated in two files: `app/assets/stylesheets/blorgh/articles.css`. You'll see how to use these a little later. -You can see what the engine has so far by running `bin/rails db:migrate` at the root +You can see what the engine has so far by running `rails db:migrate` at the root of our engine to run the migration generated by the scaffold generator, and then running `rails server` in `test/dummy`. When you open `http://localhost:3000/blorgh/articles` you will see the default scaffold that has @@ -457,7 +464,7 @@ rather than visiting `/articles`. This means that instead of Now that the engine can create new articles, it only makes sense to add commenting functionality as well. To do this, you'll need to generate a comment -model, a comment controller and then modify the articles scaffold to display +model, a comment controller, and then modify the articles scaffold to display comments and allow people to create new ones. From the application root, run the model generator. Tell it to generate a @@ -465,7 +472,7 @@ From the application root, run the model generator. Tell it to generate a and `text` text column. ```bash -$ bin/rails generate model Comment article_id:integer text:text +$ rails generate model Comment article_id:integer text:text ``` This will output the following: @@ -485,7 +492,7 @@ called `Blorgh::Comment`. Now run the migration to create our blorgh_comments table: ```bash -$ bin/rails db:migrate +$ rails db:migrate ``` To show the comments on an article, edit `app/views/blorgh/articles/show.html.erb` and @@ -533,12 +540,12 @@ directory at `app/views/blorgh/comments` and in it a new file called ```html+erb <h3>New comment</h3> -<%= form_for [@article, @article.comments.build] do |f| %> +<%= form_with(model: [@article, @article.comments.build], local: true) do |form| %> <p> - <%= f.label :text %><br> - <%= f.text_area :text %> + <%= form.label :text %><br> + <%= form.text_area :text %> </p> - <%= f.submit %> + <%= form.submit %> <% end %> ``` @@ -559,7 +566,7 @@ The route now exists, but the controller that this route goes to does not. To create it, run this command from the application root: ```bash -$ bin/rails g controller comments +$ rails g controller comments ``` This will generate the following things: @@ -649,7 +656,7 @@ there isn't an application handy to test this out in, generate one using the $ rails new unicorn ``` -Usually, specifying the engine inside the Gemfile would be done by specifying it +Usually, specifying the engine inside the `Gemfile` would be done by specifying it as a normal, everyday gem. ```ruby @@ -691,17 +698,17 @@ pre-defined path which may be customizable. The engine contains migrations for the `blorgh_articles` and `blorgh_comments` table which need to be created in the application's database so that the engine's models can query them correctly. To copy these migrations into the -application run the following command from the `test/dummy` directory of your Rails engine: +application run the following command from the application's root: ```bash -$ bin/rails blorgh:install:migrations +$ rails blorgh:install:migrations ``` If you have multiple engines that need migrations copied over, use `railties:install:migrations` instead: ```bash -$ bin/rails railties:install:migrations +$ rails railties:install:migrations ``` This command, when run for the first time, will copy over all the migrations @@ -719,7 +726,7 @@ timestamp (`[timestamp_2]`) will be the current time plus a second. The reason for this is so that the migrations for the engine are run after any existing migrations in the application. -To run these migrations within the context of the application, simply run `bin/rails +To run these migrations within the context of the application, simply run `rails db:migrate`. When accessing the engine through `http://localhost:3000/blog`, the articles will be empty. This is because the table created inside the application is different from the one created within the engine. Go ahead, play around with the @@ -730,14 +737,14 @@ If you would like to run migrations only from one engine, you can do it by specifying `SCOPE`: ```bash -bin/rails db:migrate SCOPE=blorgh +rails db:migrate SCOPE=blorgh ``` This may be useful if you want to revert engine's migrations before removing it. To revert all migrations from blorgh engine you can run code such as: ```bash -bin/rails db:migrate SCOPE=blorgh VERSION=0 +rails db:migrate SCOPE=blorgh VERSION=0 ``` ### Using a Class Provided by the Application @@ -764,7 +771,7 @@ application: rails g model user name:string ``` -The `bin/rails db:migrate` command needs to be run here to ensure that our +The `rails db:migrate` command needs to be run here to ensure that our application has the `users` table for future use. Also, to keep it simple, the articles form will have a new text field called @@ -779,8 +786,8 @@ added above the `title` field with this code: ```html+erb <div class="field"> - <%= f.label :author_name %><br> - <%= f.text_field :author_name %> + <%= form.label :author_name %><br> + <%= form.text_field :author_name %> </div> ``` @@ -824,7 +831,7 @@ of associating the records in the `blorgh_articles` table with the records in th To generate this new column, run this command within the engine: ```bash -$ bin/rails g migration add_author_id_to_blorgh_articles author_id:integer +$ rails g migration add_author_id_to_blorgh_articles author_id:integer ``` NOTE: Due to the migration's name and the column specification after it, Rails @@ -836,7 +843,7 @@ This migration will need to be run on the application. To do that, it must first be copied using this command: ```bash -$ bin/rails blorgh:install:migrations +$ rails blorgh:install:migrations ``` Notice that only _one_ migration was copied over here. This is because the first @@ -851,7 +858,7 @@ Copied migration [timestamp]_add_author_id_to_blorgh_articles.blorgh.rb from blo Run the migration using: ```bash -$ bin/rails db:migrate +$ rails db:migrate ``` Now with all the pieces in place, an action will take place that will associate @@ -917,7 +924,7 @@ engine: mattr_accessor :author_class ``` -This method works like its brothers, `attr_accessor` and `cattr_accessor`, but +This method works like its siblings, `attr_accessor` and `cattr_accessor`, but provides a setter and getter method on the module with the specified name. To use it, it must be referenced using `Blorgh.author_class`. @@ -978,7 +985,7 @@ Blorgh.author_class = "User" WARNING: It's very important here to use the `String` version of the class, rather than the class itself. If you were to use the class, Rails would attempt to load that class and then reference the related table. This could lead to -problems if the table wasn't already existing. Therefore, a `String` should be +problems if the table didn't already exist. Therefore, a `String` should be used and then converted to a class using `constantize` in the engine later on. Go ahead and try to create a new article. You will see that it works exactly in the @@ -994,7 +1001,7 @@ some sort of identifier by which it can be referenced. #### General Engine Configuration Within an engine, there may come a time where you wish to use things such as -initializers, internationalization or other configuration options. The great +initializers, internationalization, or other configuration options. The great news is that these things are entirely possible, because a Rails engine shares much the same functionality as a Rails application. In fact, a Rails application's functionality is actually a superset of what is provided by @@ -1016,11 +1023,11 @@ Testing an engine When an engine is generated, there is a smaller dummy application created inside it at `test/dummy`. This application is used as a mounting point for the engine, to make testing the engine extremely simple. You may extend this application by -generating controllers, models or views from within the directory, and then use +generating controllers, models, or views from within the directory, and then use those to test your engine. The `test` directory should be treated like a typical Rails testing environment, -allowing for unit, functional and integration tests. +allowing for unit, functional, and integration tests. ### Functional Tests @@ -1318,7 +1325,7 @@ engine. Assets within an engine work in an identical way to a full application. Because the engine class inherits from `Rails::Engine`, the application will know to -look up assets in the engine's 'app/assets' and 'lib/assets' directories. +look up assets in the engine's `app/assets` and `lib/assets` directories. Like all of the other components of an engine, the assets should be namespaced. This means that if you have an asset called `style.css`, it should be placed at @@ -1357,8 +1364,8 @@ that only exists for your engine. In this case, the host application doesn't need to require `admin.css` or `admin.js`. Only the gem's admin layout needs these assets. It doesn't make sense for the host app to include `"blorgh/admin.css"` in its stylesheets. In this situation, you should -explicitly define these assets for precompilation. This tells sprockets to add -your engine assets when `bin/rails assets:precompile` is triggered. +explicitly define these assets for precompilation. This tells Sprockets to add +your engine assets when `rails assets:precompile` is triggered. You can define assets for precompilation in `engine.rb`: @@ -1410,3 +1417,115 @@ module MyEngine end end ``` + +Active Support On Load Hooks +---------------------------- + +Active Support is the Ruby on Rails component responsible for providing Ruby language extensions, utilities, and other transversal utilities. + +Rails code can often be referenced on load of an application. Rails is responsible for the load order of these frameworks, so when you load frameworks, such as `ActiveRecord::Base`, prematurely you are violating an implicit contract your application has with Rails. Moreover, by loading code such as `ActiveRecord::Base` on boot of your application you are loading entire frameworks which may slow down your boot time and could cause conflicts with load order and boot of your application. + +On Load hooks are the API that allow you to hook into this initialization process without violating the load contract with Rails. This will also mitigate boot performance degradation and avoid conflicts. + +## What are `on_load` hooks? + +Since Ruby is a dynamic language, some code will cause different Rails frameworks to load. Take this snippet for instance: + +```ruby +ActiveRecord::Base.include(MyActiveRecordHelper) +``` + +This snippet means that when this file is loaded, it will encounter `ActiveRecord::Base`. This encounter causes Ruby to look for the definition of that constant and will require it. This causes the entire Active Record framework to be loaded on boot. + +`ActiveSupport.on_load` is a mechanism that can be used to defer the loading of code until it is actually needed. The snippet above can be changed to: + +```ruby +ActiveSupport.on_load(:active_record) { include MyActiveRecordHelper } +``` + +This new snippet will only include `MyActiveRecordHelper` when `ActiveRecord::Base` is loaded. + +## How does it work? + +In the Rails framework these hooks are called when a specific library is loaded. For example, when `ActionController::Base` is loaded, the `:action_controller_base` hook is called. This means that all `ActiveSupport.on_load` calls with `:action_controller_base` hooks will be called in the context of `ActionController::Base` (that means `self` will be an `ActionController::Base`). + +## Modifying code to use `on_load` hooks + +Modifying code is generally straightforward. If you have a line of code that refers to a Rails framework such as `ActiveRecord::Base` you can wrap that code in an `on_load` hook. + +### Example 1 + +```ruby +ActiveRecord::Base.include(MyActiveRecordHelper) +``` + +becomes + +```ruby +ActiveSupport.on_load(:active_record) { include MyActiveRecordHelper } # self refers to ActiveRecord::Base here, so we can simply #include +``` + +### Example 2 + +```ruby +ActionController::Base.prepend(MyActionControllerHelper) +``` + +becomes + +```ruby +ActiveSupport.on_load(:action_controller_base) { prepend MyActionControllerHelper } # self refers to ActionController::Base here, so we can simply #prepend +``` + +### Example 3 + +```ruby +ActiveRecord::Base.include_root_in_json = true +``` + +becomes + +```ruby +ActiveSupport.on_load(:active_record) { self.include_root_in_json = true } # self refers to ActiveRecord::Base here +``` + +## Available Hooks + +These are the hooks you can use in your own code. + +To hook into the initialization process of one of the following classes use the available hook. + +| Class | Available Hooks | +| --------------------------------- | ------------------------------------ | +| `ActionCable` | `action_cable` | +| `ActionController::API` | `action_controller_api` | +| `ActionController::API` | `action_controller` | +| `ActionController::Base` | `action_controller_base` | +| `ActionController::Base` | `action_controller` | +| `ActionController::TestCase` | `action_controller_test_case` | +| `ActionDispatch::IntegrationTest` | `action_dispatch_integration_test` | +| `ActionDispatch::SystemTestCase` | `action_dispatch_system_test_case` | +| `ActionMailer::Base` | `action_mailer` | +| `ActionMailer::TestCase` | `action_mailer_test_case` | +| `ActionView::Base` | `action_view` | +| `ActionView::TestCase` | `action_view_test_case` | +| `ActiveJob::Base` | `active_job` | +| `ActiveJob::TestCase` | `active_job_test_case` | +| `ActiveRecord::Base` | `active_record` | +| `ActiveSupport::TestCase` | `active_support_test_case` | +| `i18n` | `i18n` | + +## Configuration hooks + +These are the available configuration hooks. They do not hook into any particular framework, but instead they run in context of the entire application. + +| Hook | Use Case | +| ---------------------- | ---------------------------------------------------------------------------------- | +| `before_configuration` | First configurable block to run. Called before any initializers are run. | +| `before_initialize` | Second configurable block to run. Called before frameworks initialize. | +| `before_eager_load` | Third configurable block to run. Does not run if `config.eager_load` set to false. | +| `after_initialize` | Last configurable block to run. Called after frameworks initialize. | + +### Example + +`config.before_configuration { puts 'I am called before any initializers' }` |