If you’re just learning Ruby on Rails, you may be confused as to when to generate individual models, resources or scaffolding, and what files are created by each command.

Say you want to generate a Test model with a name.  You could either generate the model individually, generate resources, or generate scaffolding, as follows:

rails g model Test name:text

rails g resource Test name:text

rails g scaffold Test name:text

What’s the difference between each of the above?

Generating Individual Models

Entering rails g model Test name:text in your command line will generate the following:

(1) A model file test.rb in your models directory:

class Test < ActiveRecord::Base
end

(2) A migration file timestamp_create_tests.rb in your db/migrate directory:

class CreateTests < ActiveRecord::Migration
  def change
    create_table :tests do |t|
      t.text :name

      t.timestamps
    end
  end
end

Generating Resources

Entering rails g resource Test name:text in your command line will generate the following:

(1) A model file test.rb in your models directory:

class Test < ActiveRecord::Base
end

(2) A migration file timestamp_create_tests.rb  in your db/migrate directory:

class CreateTests < ActiveRecord::Migration
  def change
    create_table :tests do |t|
      t.text :name

      t.timestamps
    end
  end
end

(3) a tests_controller.rb file in your controllers directory.  This controller will be an empty shell:

class TestsController < ApplicationController
end

(4) resources :tests routes in your routes.rb file.

Generating Scaffolding

Entering rails g scaffold Test name:text in your command line will generate the following:

(1) A model file test.rb in your models directory:

class Test < ActiveRecord::Base
end

(2) A migration file timestamp_create_tests.rb in your db/migrate directory:

class CreateTests < ActiveRecord::Migration
  def change
    create_table :tests do |t|
      t.text :name

      t.timestamps
    end
  end
end

(3) A tests_controller.rb file in your controllers directory.  When a scaffold is generated, seven public methods and two private methods will be added to your controller:

class TestsController < ApplicationController
  before_action :set_test, only: [:show, :edit, :update, :destroy]

  # GET /tests
  # GET /tests.json
  def index
    @tests = Test.all
  end

  # GET /tests/1
  # GET /tests/1.json
  def show
  end

  # GET /tests/new
  def new
    @test = Test.new
  end

  # GET /tests/1/edit
  def edit
  end

  # POST /tests
  # POST /tests.json
  def create
    @test = Test.new(test_params)

    respond_to do |format|
      if @test.save
        format.html { redirect_to @test, notice: 'Test was successfully created.' }
        format.json { render action: 'show', status: :created, location: @test }
      else
        format.html { render action: 'new' }
        format.json { render json: @test.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /tests/1
  # PATCH/PUT /tests/1.json
  def update
    respond_to do |format|
      if @test.update(test_params)
        format.html { redirect_to @test, notice: 'Test was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @test.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /tests/1
  # DELETE /tests/1.json
  def destroy
    @test.destroy
    respond_to do |format|
      format.html { redirect_to tests_url }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_test
      @test = Test.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def test_params
      params.require(:test).permit(:name)
    end
end

(4) resources :tests routes in your routes.rb file.

(5) Seven corresponding view files in your views directory: (a) _form.html.erb, (b) edit.html.erb, (c) index.html.erb, (d) index.json.jbuilder, (e) new.html.erb, (f) show.html.erb and (g) show.json.jbuilder. Each view will contain html and embedded ruby.

To learn more about the routes generated by resources, please read Getting Started with Ruby on Rails.

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Koren Leslie Cohen

Product manager at Facebook. Former senior product manager at Dollar Shave Club in Los Angeles and software engineer at J.Crew / Madewell in New York City. Recovering trial lawyer.

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