July 17, 2016

Generators are one of Rails' greatest features and one of the reasons it's so easy to get up and running with new Rails projects. Unfortunately, they tend to be accompanied by a lot of extra files you may or may not need. Whenever I'm using generators, I like to know exactly what I'm getting into file-wise, ideally via a reference that lists what files I can expect to have when running them. Yes, this exists in the form of man pages for each individual generator, but I prefer to be able to see many at once, comparing my options. I've yet to see this kind of resource. Until now.

For this guide, I'll be using a Rails 5.0 default application with no additional gems and no modifications to the generator system. If you're looking to modify the content created by the generators, Thoughtbot has a helpful blog post on that here. Railsguides.net also has a great post on generator usage and getting more out of the basic generators here. With that said...

Note: the commands for running rails generators are rails generate [type], rails g [type] for ease. I'll just be using g instead of generate here.

rails g migration

This generator will just create a migration file under db/migrate as named with a timestamp. For example, rails g migration CreateUsers will generate a file called 20150717155949_create_users.rb and it will contain the following text:

class CreateUsers < ActiveRecord::Migration[5.0]
 def change
  create_table :users do |t|
  end
 end
end

You can also pass arguments to this generator for whatever arguments you're creating/modifying, like so: rails g migration AddBirthdateToUsers birthdate:date

rails g model

The model generator creates a model file for the named resource, a database migration to create the appropriate table, and the appropriate test files. So, new files for rails g model User are as follows:

app/models/user.rb
test
 models/user_test.rb
 fixtures/users.yml

rails g controller

The controller generator creates a controller, a controller test file, and an associated helper. You can also pass arguments in the form of controller actions to this generator. So, rails g controller Static index will create the following:

app
 assets
  javascripts/static.coffee
  stylesheets/static.scss
 controllers/static_controller.rb
 helpers/static_helper.rb
 views/static/index.html.erb
test
 controllers/static_controller_test.rb

as well as routes for your defined actions in your config/routes.rb file.

rails g scaffold

This is the big kahuna. The scaffold creates a model, controller, views, assets (styles and javascript), tests, and routes for the designated resource, as well as a database migration for the new table. The controller files are fully operable, complete with index, create, new, edit, show, update, destroy methods. Controller test files are also full of working tests. rails g scaffold Post title body:text will create the following files:

app
 assets
 javascripts/posts.coffee
 stylesheets/posts.scss
 controllers/posts_controller.rb
 helpers/posts_helper.rb
 models/post.rb
 views/posts
  _form.html.erb
  index.html.erb
  index.json.jbuilder
  edit.html.erb
  show.html.erb
  show.json.jbuilder
  new.html.erb
test
 controllers/post_controller_test.rb
 fixtures/posts.yml
 models/post_test.rb

Note: adding an attribute argument with no defined datatype defaults to the string type.

rails g resource

Unlike the scaffold generator, this generator doesn't create views or add methods to the generated controller. In addition to the new table's database migration and a resources :posts line in your config/routes.rb file, rails g resource Purchase user_id:integer will create:

app
 assets
  javascripts/posts.coffee
  stylesheets/posts.scss
 controllers/posts_controller.rb
 helpers/posts_helper.rb
 models/post.rb
 views/posts
test
 controllers/post_controller_test.rb
 fixtures/posts.yml
 models/post_test.rb

rails g scaffold_controller

If you like the guidance of the scaffolded controllers and front-end files, but don't need any of the data modeling functionality, this generator is for you. Like the scaffold, the controller test file will be fully populated. rails g scaffold_controller Hello will create:

app
 controllers/hellos_controller.rb
 helpers/hellos_helper.rb
 views/hellos
  index.html.erb
  index.json.jbuilder
  edit.html.erb
  show.html.erb
  show.json.jbuilder
  new.html.erb
  _form.html.erb
test/controllers/hellos_controller_test.rb

rails g mailer

This generator creates a mailer and blank mailer test files, named appropriately. rails g mailer Campaign will create:

app
 mailers/campaign_mailer.rb
 views/campaign_mailer
test/mailers
 previews/campaign_mailer_preview.rb
 campaign_mailer_test.rb

rails g helper

This simply creates a helper file, again named as you please. rails g helper Auth will create:

app/helpers/auth_helper.rb

rails g task

Similarly to the helper generator, the task generator simply creates the named rake task file. rails g task Cleanup creates:

lib/tasks/cleanup.rake

rails g job

The job generator, rails g job Import for example, creates:

app/jobs/import_job.rb
test/jobs/import_job_test.rb

rails g assets

If front-end's your thing, the assets generator creates only a javascript file and a css file as named. rails g assets Smile will create:

app/assets
javascripts/smile.coffee
stylesheets/smile.scss

rails g channel

New in Rails 5, this generator creates the necessary files for a new ActionCable channel. rails g channel Chat speak will create:

app
 assets/javascripts/channels/chat.coffee
 channels/chat_channel.rb

As of the 5.0 release, app/assets/javascripts/channels/chat.coffee will look like this:

App.chat = App.cable.subscriptions.create "ChatChannel",
 connected: ->
  # Called when the subscription is ready for use on the server

 disconnected: ->
  # Called when the subscription has been terminated by the server

 received: (data) ->
  # Called when there's incoming data on the websocket for this channel

and app/channels/chat_channel.rb will look like this:

class ChatChannel < ApplicationCable::Channel
 def subscribed
  # stream_from "some_channel"
 end

 def unsubscribed
  # Any cleanup needed when channel is unsubscribed
 end
end

rails d

Finally, this acts as an undo button when you run a generator. Just as you'd run rails g model User, you can run rails d model User to delete all files generated with the model generator. You can use this with any of the generators listed above. Super useful if you find you've made a typo somewhere in your naming, or realize you don't really need all those files when you scaffold.

I've personally wanted a reference for these generators anytime I use them, so I hope this guide was as helpful for you as it is for me.