Rails Engines & Plugins Cheatsheet

Rails Engines are mini-applications packaged as Ruby gems that provide their own models, controllers, views, routes, and migrations.

Generating a Rails Engine Plugin

# Generate a mountable, full-stack engine with isolated namespace
bin/rails plugin new my_engine --mountable --skip-bundle

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Engine Architecture

Inside lib/my_engine/engine.rb:

module MyEngine
  class Engine < ::Rails::Engine
    isolate_namespace MyEngine

    initializer "my_engine.assets" do |app|
      app.config.assets.precompile += %w[my_engine/application.css]
    end
  end
end

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Mounting in Host Application

In the host application's config/routes.rb:

Rails.application.routes.draw do
  mount MyEngine::Engine => "/blog"
end

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Engine Migrations

To copy engine migrations into the parent application:

bin/rails my_engine:install:migrations
bin/rails db:migrate

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References

• Getting Started with Engines Guide
• Rails Overview Cheatsheet