Controller

Controller Builder

When to use

Use this skill when asked to create a new controller or add actions to an existing controller in any Rails app under apps/.

Working Directory

Determine which app the controller belongs to. Default is apps/rails_application/ unless specified.

Step-by-step process

1. Gather requirements

Before writing any code, clarify:

• Which read model the controller queries (must already exist)
• Which domain commands the controller dispatches (must already exist)
• What actions are needed (index, show, new, create, edit, update, destroy, custom)
• Whether it lives in a namespace (e.g. admin/, client/)

2. Write integration tests first (TDD)

Create a test file at test/integration/{controller_name}_test.rb.

require "test_helper"

class ResourceNameTest < InMemoryRESIntegrationTestCase
  def test_list_resources
    get "/resources"
    assert_response :success
  end

  def test_create_resource
    post "/resources", params: { name: "Test" }
    follow_redirect!
    assert_select("td", "Test")
  end

  def test_update_resource
    resource_id = create_resource("Original")

    patch "/resources/#{resource_id}", params: { name: "Updated" }
    follow_redirect!
    assert_select("td", "Updated")
  end

  private

  def create_resource(name)
    post "/resources", params: { name: name }
    follow_redirect!
    # extract ID from page or use read model facade
    ReadModel.all.last.uid
  end
end

Integration test conventions:

• Inherit from InMemoryRESIntegrationTestCase
• Use HTTP verbs: get, post, patch, delete
• Use follow_redirect! after redirecting actions
• Assert with assert_response, assert_select
• Extract setup into private helper methods
• Never dispatch commands directly — always go through HTTP
• Never access AR models directly — use read model facade methods if needed

3. Add routes

Add to config/routes.rb:

resources :resources, only: [:index, :show, :new, :create, :edit, :update, :destroy] do
  member do
    post :custom_action
  end
  collection do
    delete :clear_all
  end
end

Route conventions:

• Use RESTful resources with only: to limit actions
• Custom actions go in member do (operates on one record) or collection do (operates on many)
• Namespace for grouped controllers:

  namespace :admin do
    resources :stores, only: [:index, :new, :create]
  end
  

4. Create the controller

class ResourcesController < ApplicationController
  def index
    @resources = ReadModel.all
  end

  def show
    @resource = ReadModel.find_by_uid(params[:id])
  end

  def new
    @resource_id = SecureRandom.uuid
  end

  def create
    ActiveRecord::Base.transaction do
      command_bus.call(Domain::CreateResource.new(
        resource_id: params[:resource_id],
        name: params[:name]
      ))
    end
    redirect_to resources_path, notice: "Resource was successfully created"
  end

  def edit
    @resource = ReadModel.find_by_uid(params[:id])
  end

  def update
    command_bus.call(Domain::UpdateResource.new(
      resource_id: params[:id],
      name: params[:name]
    ))
    redirect_to resource_path(params[:id]), notice: "Resource was successfully updated"
  end

  def destroy
    command_bus.call(Domain::RemoveResource.new(resource_id: params[:id]))
    redirect_to resources_path, notice: "Resource was successfully removed"
  end
end

5. Controller conventions

Command dispatch:

• Use command_bus.call(Command.new(...)) to dispatch commands
• Wrap multiple commands in ActiveRecord::Base.transaction do ... end
• Generate UUIDs before dispatch: id = SecureRandom.uuid

Read model queries:

• Always use facade methods: ReadModel.all, ReadModel.find_by_uid(id)
• Never access ActiveRecord models directly

Redirects:

• After successful writes: redirect_to path, notice: "..."
• After errors: redirect_to path, alert: "..."

Error handling:

• Use rescue/else for domain exceptions:

  def submit
    SomeService.new(params[:id]).call
  rescue Domain::SomeError => e
    redirect_to edit_path(params[:id]), alert: e.message
  else
    redirect_to show_path(params[:id]), notice: "Success"
  end
  

Before actions:

• Use for authorization, ownership checks, loading shared data:

  before_action :load_resource, only: [:show, :edit, :update]
  
  private
  
  def load_resource
    @resource = ReadModel.find_by_uid(params[:id])
  end
  

6. Form objects (when validation is needed)

For non-trivial forms, create a form object in the controller file or a separate file:

class ResourceForm
  include ActiveModel::Model
  include ActiveModel::Attributes
  include ActiveModel::Validations

  attribute :name, :string
  attribute :price, :decimal
  attribute :resource_id, :string

  validates :name, presence: true
  validates :price, presence: true, numericality: { greater_than: 0 }
end

Use in the controller:

def create
  form = ResourceForm.new(**resource_params)
  unless form.valid?
    return render "new", locals: { errors: form.errors }, status: :unprocessable_entity
  end

  ActiveRecord::Base.transaction do
    command_bus.call(Domain::CreateResource.new(resource_id: form.resource_id, name: form.name))
  end
  redirect_to resources_path, notice: "Created"
end

7. Service objects (when logic is complex)

When a controller action involves complex coordination (multiple commands, event subscriptions, error handling), extract to a service:

# app/services/{namespace}/submit_service.rb
module Namespace
  class SubmitService
    def initialize(id)
      @id = id
    end

    def call
      ActiveRecord::Base.transaction do
        command_bus.call(Domain::Submit.new(id: @id))
      end
    end

    private

    def command_bus
      Rails.configuration.command_bus
    end
  end
end

8. Namespaced controllers

For controllers under a namespace (e.g. admin/, client/):

# app/controllers/admin/resources_controller.rb
module Admin
  class ResourcesController < ApplicationController
    def index
      @resources = ReadModel.all
    end
  end
end

With a base controller for shared behavior:

# app/controllers/client/base_controller.rb
module Client
  class BaseController < ApplicationController
    layout "client_panel"
    before_action :ensure_logged_in

    private

    def ensure_logged_in
      # auth check
    end
  end
end

# app/controllers/client/orders_controller.rb
module Client
  class OrdersController < BaseController
    def index
      @orders = ClientOrders.orders_for_client(current_client_id)
    end
  end
end

9. Create views

Create ERB views in app/views/{controller_name}/:

• index.html.erb — list view
• show.html.erb — detail view
• new.html.erb — form for creating
• edit.html.erb — form for editing

Views query data via instance variables set in controller (@resources, @resource).

10. Run verification

1. rails test test/integration/{test_file}.rb — integration tests pass
2. make test — all tests green

Key conventions

• Controllers are thin — dispatch commands and query read models
• Complex logic goes into service objects
• Multiple commands wrapped in transactions
• UUIDs generated in controller before command dispatch
• Read model facade methods for all queries
• Integration tests exercise the full HTTP stack
• Test-first TDD

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