This article shows how to design your Rails gem covering aspects of integration with main Rails application.
Contents
– Paths
– Routes
– Add functionality to controller
– Improving (Extending or overriding) Engine functionality
– Helpers
– Assets
Paths
* access gem root path from the app
spec = Gem::Specification.find_by_name("your_gem_name")
gem_root = spec.gem_dir
yaml_obj = YAML.load(gem_root + "/file_name.yaml")
Routes
Routes inside an engine are isolated from the application by default.
The application and its engines can have routes with the same names.
Routes defined in engine:
# /myengine/config/routes.rb
Myengine::Engine.routes do
resources :articles
end
Mount engine to the main app:
# config/routes.rb
Rails.application.routes.draw do
# app routes
mount Myengine::Engine => "/myengine", :as => "myengine"
end
Engine’s pages will have URL prefix ‘myengine/’. For example, URL for articles page from Engine:
http://mysite.com/myengine/articles
Access Engine’s routes from the main app
Access engine’s route from the main app view:
# use the name specified in mount in 'as': mount Myengine::Engine => "/myenginepath", :as => "myengine"
= link_to 'Articles from Engine', myengine.articles_path
# this will try to find route defined in the main app, NOT from engine
= link_to 'Articles', articles_path
from any place in app (in controller, or in a class in lib/ )
Myengine::Engine.routes.url_helpers.articles_path
Access main app’s routes in Engine
routes defined in app:
# config/routes.rb
Rails.application.routes.draw do
resources :users
# mount engine
mount Myengine::Engine => "/", :as => "myengine"
end
Access app’s routes from engine’s view:
# myengine/app/views/somedir/someview.html.haml
= link_to 'Users', main_app.users_path
Merge engine and app routes
If you want the two sets of routes to be merged, you can use a non-isolated engine.
Removing the isolated_namespace in the engine definition:
# myengine/lib/myengine/engine.rb
module Myengine
class Engine < Rails::Engine
#isolate_namespace Myengine # remove this line
...
end
end
Define routes in Engine with Rails.application.routes.draw, NOT Myengine::Engine.routes.draw:
# myengine/config/routes.rb
Rails.application.routes.draw do
resources :articles
end
Remove `mount` in the main app:
App::Application.routes.draw do
#mount Myengine::Engine => "/myengine" # remove this line
end
Now you can access routes from app and engine just using:
= link_to 'Articles', articles_path
Find more in [discussion on stackoverflow](http://stackoverflow.com/questions/7588870/engine-routes-in-application-controller#answer-7622755).
Controller
* We want to create a method in the Engine which will extend functionality of our app controller like this:
# Main app controller
class MyController < ApplicationController
include UsefulController::Useful
add_smth_useful :opt1, {opt1: v1, opt2: v2}
end
* Create method add_smth_useful in the Engine which will add action `myaction` to the main app controller
# Engine: app/controllers/useful_controller.rb
require 'active_support/concern'
module UsefulController
module Useful
extend ActiveSupport::Concern
included do
# method to add to controller
def newmethod1
...
end
end
module ClassMethods
def add_smth_useful(arg1, options = {})
# add method to the controller
define_method("myaction") do
# action code
# render ...
end
end
end
end
end
Improving (Extending or overriding) Engine functionality
A common task after including Engine in your Rails app is extending some classes (models, controllers, other classes) defined in the Engine.
It can be done using Decorator pattern.
There are two options of extending a class defined in Engine:
- use Class@class_eval
- use ActiveSupport::Concern
For simple class modifications, use Class#class_eval.
For complex class modifications, consider using ActiveSupport::Concern.
Read more in [Rails guides](http://edgeguides.rubyonrails.org/engines.html).
use Class class_eval to override class defined in Gem/Engine
# lib/myengine/engine.rb
module Myengine
class Engine < ::Rails::Engine
isolate_namespace Myengine
config.to_prepare do
Dir.glob(Rails.root + "app/decorators/**/*_decorator*.rb").each do |c|
require_dependency(c)
end
end
end
end
in the Engine:
# Myengine/app/models/article.rb
class Article < ActiveRecord::Base
has_many :comments
def summary
"#{title}"
end
end
in the main app:
# MyApp/app/decorators/models/blorgh/article_decorator.rb
Myengine::Article.class_eval do
# add new method
def time_since_created
Time.current - created_at
end
# override the method
def summary
"#{title} - #{truncate(text)}"
end
end
Extend Engine class using ActiveSupport::Concern
We have a class defined in Engine:
# myengine/lib/myengine/mymodule/myclass.rb
module Myengine
module Mymodule
class Myclass
include Myengine::Concerns::Mymodule::Myclass
..
end
end
end
Add concern to Engine:
# myengine/lib/concerns/mymodule/myclass.rb
module Myengine::Concerns::Mymodule::Myclass
extend ActiveSupport::Concern
included do
..
end
def my_object_method
'it is engine'
end
module ClassMethods
# will be overridden in the main app
def my_class_method
[]
end
end
end
Use concern in the main app:
# myapp/lib/myengine/mymodule/myclass.rb
module Myengine
module Mymodule
class Myclass
include Myengine::Concerns::Mymodule::Myclass
# override class method
def self.my_class_method
['1', '2', '3']
end
# override object method
def my_object_method
'this is app'
end
end
end
end
Extend Engine model class using ActiveSupport::Concern
We have a model defined in Engine (gem).
# myengine/app/models/myengine/mymodel.rb
module Myengine
class Myclass < ActiveRecord::Base
end
end
One way to reopen a class in main app is defining an extension in app/extensions folder.
# myapp/app/extensions/myengine/mymodel.rb
require Myengine::Engine.root.join('app/models/myengine/mymodel')
module MyengineExtensions
extend ActiveSupport::Concern
included do
before_validation :_before_validation
after_save :_after_save
def _before_validation
end
def _after_save
end
end
module InstanceMethods
end
module ClassMethods
end
end
Myengine::Mymodel.send(:include, MyengineExtensions)
Use helpers defined in the Engine
* Isolated engine's helpers
Sometimes you may want to isolate engine, but use helpers that are defined for it. If you want to share just a few specific helpers you can add them to application's helpers in ApplicationController:
class ApplicationController < ActionController::Base
helper MyEngine::SharedEngineHelper
end
If you want to include all of the engine's helpers, you can use the helper method on an engine's instance:
class ApplicationController < ActionController::Base
helper MyEngine::Engine.helpers
end
It will include all of the helpers from engine's directory. Take into account that this does not include helpers defined in controllers with helper_method or other similar solutions, only helpers defined in the helpers directory will be included.
Access Engine's assets from main app
A gem may come with assets - css, js or image files.
We want to use assets included in gem from main application.
Gem/Engine structure:
* package.json
* app/assets/images/mygem/
* img1.jpg
* app/assets/javascripts/mygem/
* mygem1.js
* app/assets/stylesheets/mygem/
* style1.scss
Place Gem's assets in folder 'mygem' so that they will be distinct from main app's assets.
* include asset files to be precompiled:
define precompiled assets in Gem:
config/initializers/assets.rb
Rails.application.config.assets.precompile += %w( mygem/style1.css )
Rails.application.config.assets.precompile += %w( mygem/mygem1.js )
/lib/mygem/engine.rb
module Mygem
class Engine < ::Rails::Engine
isolate_namespace Optimacms
# for Rails 5
config.enable_dependency_loading = false
config.eager_load_paths += %W( #{Mygem::Engine.root}/lib )
config.watchable_dirs['lib'] = [:rb] if Rails.env.development?
config.watchable_dirs['app/helpers'] = [:rb] if Rails.env.development?
config.autoload_paths += Dir["#{Mygem::Engine.root}/app/helpers/"]
config.autoload_paths += Dir["#{Mygem::Engine.root}/lib/"]
config.autoload_paths += Dir["#{Mygem::Engine.root}/lib/**/"]
#config.autoload_paths += Dir["#{Mygem::Engine.root}/lib/concerns/"]
#config.autoload_paths += Dir["#{Mygem::Engine.root}/lib/concerns/**/"]
config.autoload_paths += Dir["#{Mygem::Engine.root}/lib/mygem/"]
config.before_initialize do
ActiveSupport.on_load :action_controller do
include ::Optimacms::Mycontroller
::ActionController::Base.helper Optimacms::Engine.helpers
end
end
initializer "optimacms assets precompile" do |app|
app.config.assets.precompile += %w(mygem/mygem1.js.css mygem/style1.css )
end
end
end
Use assets in Gem
Use Gem's assets in the Gem the same way as in usual Rails app.
* in view `app/views/mygem/folder1/example.html.haml`:
= javascript_include_tag "mygem/mygem1.js"
= stylesheet_link_tag 'mygem/style1', media: 'all'
Use Gem's assets in main application.
* main app's js file `app/assets/stylesheets/myapp.js`
//= require mygem/mygem1.js
* main app's scss file `app/assets/stylesheets/myapp.scss`
...
@import "mygem/style1";
Use npm packages in gem
A gem may include node packages with yarn.
In order to use js, css, image, font files in a node module with Rails assets pipeline we need to add those files to assets precompile paths:
in Gem file config/initializers/assets.rb:
Rails.application.config.assets.paths << Mygem::Engine.root.join('node_modules')
Now you can use files from a package in gem's assets files.
* package.json - this file is part of the Gem
{
"name": "mygem",
"version": "1.0.0",
"main": "index.js",
"repository": "git@github.com:maxivak/mygem.git",
"author": "mmx
"license": "MIT",
"dependencies": {
"jquery": "3.2.1",
"jquery-ui-dist": "1.12.1",
"jquery-ujs": "1.2.2",
"bootstrap": "4.1.0",
"popper.js": "1.14.3",
"font-awesome": "4.7.0"
}
}
* use assets from node modules in Gem
* app/assets/javascripts/mygem/mygem1.js
//= require jquery/dist/jquery
//= require jquery-ujs
//= require jquery-ui-dist/jquery-ui
//= require popper.js/dist/umd/popper.js
//= require bootstrap/dist/js/bootstrap
* app/assets/stylesheets/mygem/style1.scss
...
// Bootstrap and its default variables
@import "bootstrap/scss/bootstrap";
* IMPORTANT! You may have problems if a node module refers to assets without using Rails asset helpers.
For example,
* node module includes css file which refers to images:
* css/some_module.css
.somestyle{
background-image: url("../img/back1.jpg");
}
* module has images im `img` folder.
Then it will not work in Rails.
To fix this you have to change url(..) with asset-url(..) in css files in the module:
* rename css files to scss
* scss/some_module.scss:
.somestyle{
background-image: asset-url("module-name/img/back1.jpg");
}
References:
* font-awesome package with Rails asset pipeline:
* https://stackoverflow.com/questions/48572272/rails-asset-pipeline-working-with-fonts-and-yarn/49202226#49202226
* https://stackoverflow.com/questions/42059621/rails-5-rails-assets-fontawesome-does-not-load-fonts/49202142#49202142