To generate an ActiveRecord model that automagically creates the correct db migrations & boilerplate test files for your model, enter this command

rails generate model NAME column_name:column_type

'NAME' is the name of the model. 'field' is the name of the column in the DB table and 'type' is the column type (e.g. name:string or body:text). Check the Remarks section for a list of supported column types.

To setup foreign keys, add belongs_to:model_name.

So say you wanted to setup a User model that has a username, email and belongs to a School, you would type in the following

rails generate model User username:string email:string school:belongs_to

rails g is shorthand for rails generate. This would produce the same result

rails g model User username:string email:string school:belongs_to

You can generate a rails migration file from the terminal using the following command:

rails generate migration NAME [field[:type][:index] field[:type][:index]] [options]

For a list of all the options supported by the command, you could run the command without any arguments as in rails generate migration.

For example, if you want to add first_name and last_name fields to users table, you can do:

rails generate migration AddNamesToUsers last_name:string first_name:string

Rails will create the following migration file:

class AddNamesToUsers < ActiveRecord::Migration[5.0]
  def change
    add_column :users, :last_name, :string
    add_column :users, :first_name, :string
  end
end

Now, apply the pending migrations to the database by running the following in the terminal:

rake db:migrate

rails db:migrate

Note: For even less typing, you can replace generate with g.

DISCLAIMER: Scaffolding is not recommended unless it's for very conventional CRUD apps/testing. This may generate a lot of files(views/models/controllers) that are not needed in your web application thus causing headaches(bad :().

To generate a fully working scaffold for a new object, including model, controller, views, assets, and tests, use the rails g scaffold command.

$ rails g scaffold Widget name:string price:decimal
    invoke  active_record
    create    db/migrate/20160722171221_create_widgets.rb
    create    app/models/widget.rb
    invoke    test_unit
    create      test/models/widget_test.rb
    create      test/fixtures/widgets.yml
    invoke  resource_route
     route    resources :widgets
    invoke  scaffold_controller
    create    app/controllers/widgets_controller.rb
    invoke    erb
    create      app/views/widgets
    create      app/views/widgets/index.html.erb
    create      app/views/widgets/edit.html.erb
    create      app/views/widgets/show.html.erb
    create      app/views/widgets/new.html.erb
    create      app/views/widgets/_form.html.erb
    invoke    test_unit
    create      test/controllers/widgets_controller_test.rb
    invoke    helper
    create      app/helpers/widgets_helper.rb
    invoke    jbuilder
    create      app/views/widgets/index.json.jbuilder
    create      app/views/widgets/show.json.jbuilder
    invoke  assets
    invoke    javascript
    create      app/assets/javascripts/widgets.js
    invoke    scss
    create      app/assets/stylesheets/widgets.scss

Then you can run rake db:migrate to set up the database table.

Then you can visit http://localhost:3000/widgets and you'll see a fully functional CRUD scaffold.

we can create a new controller with rails g controller command.

$ bin/rails generate controller controller_name

The controller generator is expecting parameters in the form of generate controller ControllerName action1 action2.

The following creates a Greetings controller with an action of hello.

$ bin/rails generate controller Greetings hello

You will see the following output

     create  app/controllers/greetings_controller.rb
      route  get "greetings/hello"
     invoke  erb
     create    app/views/greetings
     create    app/views/greetings/hello.html.erb
     invoke  test_unit
     create    test/controllers/greetings_controller_test.rb
     invoke  helper
     create    app/helpers/greetings_helper.rb
     invoke  assets
     invoke    coffee
     create      app/assets/javascripts/greetings.coffee
     invoke    scss
     create      app/assets/stylesheets/greetings.scss

This generates the following

It will also add routes for each action in routes.rb