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Diffstat (limited to 'guides/source/engines.md')
| -rw-r--r-- | guides/source/engines.md | 142 |
1 files changed, 129 insertions, 13 deletions
diff --git a/guides/source/engines.md b/guides/source/engines.md index 0020112a1c..8d81296fa5 100644 --- a/guides/source/engines.md +++ b/guides/source/engines.md @@ -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 -------------------------------------------------------------------------------- @@ -59,10 +60,10 @@ only be enhancing it, rather than changing it drastically. 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 +[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 @@ -345,6 +346,9 @@ 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 @@ -533,12 +537,12 @@ 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 %> ``` @@ -649,7 +653,7 @@ 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 @@ -779,8 +783,8 @@ 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> ``` @@ -917,7 +921,7 @@ 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 +982,7 @@ 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 @@ -1318,7 +1322,7 @@ 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 @@ -1357,7 +1361,7 @@ 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 +explicitly define these assets for precompilation. This tells Sprockets to add your engine assets when `bin/rails assets:precompile` is triggered. You can define assets for precompilation in `engine.rb`: @@ -1410,3 +1414,115 @@ 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' }` |