Ruby on Rails Rails Engine - Modular Rails Create a modular app
Example
# Getting started
First, let’s generate a new Ruby on Rails application:
rails new ModularTodo
The next step is to generate an engine!
cd ModularTodo && rails plugin new todo --mountable
We will also create an ‘engines’ folder to store the engines (even if we just have one!).
mkdir engines && mv todo ./engines
Engines, just like gems, come with a gemspec file. Let’s put some real values to avoid warnings.
#ModularTodo/engines/todo/todo.gemspec
$:.push File.expand_path("../lib", __FILE__)
#Maintain your gem's version:
require "todo/version"
#Describe your gem and declare its dependencies:
Gem::Specification.new do |s|
s.name = "todo"
s.version = Todo::VERSION
s.authors = ["Thibault Denizet"]
s.email = ["[email protected]"]
s.homepage = "//samurails.com"
s.summary = "Todo Module"
s.description = "Todo Module for Modular Rails article"
s.license = "MIT"
#Moar stuff
#...
end
Now we need to add the Todo engine to the parent application Gemfile.
#ModularTodo/Gemfile
#Other gems
gem 'todo', path: 'engines/todo'
Let’s run bundle install. You should see the following in the list of gems:
Using todo 0.0.1 from source at engines/todo
Great, our Todo engine is loaded correctly! Before we start coding, we have one last thing to do: mount the Todo engine. We can do that in the routes.rb file in the parent app.
Rails.application.routes.draw do
mount Todo::Engine => "/", as: 'todo'
end
We are mounting it at / but we could also make it accessible at /todo. Since we have only one module, / is fine.
Now you can fire up your server and check it in your browser. You should see the default Rails view because we didn’t define any controllers/views yet. Let’s do that now!
Building the Todo list
We are going to scaffold a model named Task inside the Todo module but to correctly migrate the database from the parent application, we need to add a small initializer to the engine.rb file.
#ModularTodo/engines/todo/lib/todo/engine.rb
module Todo
class Engine < ::Rails::Engine
isolate_namespace Todo
initializer :append_migrations do |app|
unless app.root.to_s.match(root.to_s)
config.paths["db/migrate"].expanded.each do |p|
app.config.paths["db/migrate"] << p
end
end
end
end
end
That’s it, now when we run migrations from the parent application, the migrations in the Todo engine will be loaded too.
Let’s create the Task model. The scaffold command needs to be run from the engine folder.
cd engines/todo && rails g scaffold Task title:string content:text
Run the migrations from the parent folder:
rake db:migrate
Now, we just need to define the root route inside the Todo engine:
#ModularTodo/engines/todo/config/routes.rb
Todo::Engine.routes.draw do
resources :tasks
root 'tasks#index'
end
You can play with it, create tasks, delete them… Oh wait, the delete is not working! Why?! Well, it seems JQuery is not loaded, so let’s add it to the application.js file inside the engine!
// ModularTodo/engines/todo/app/assets/javascripts/todo/application.js
//= require jquery
//= require jquery_ujs
//= require_tree .
Yay, now we can destroy tasks!
