Dhh Rails Style

DHH Rails Style

Apply DHH's Rails philosophy in two modes:

• Implementation: Write or refactor code with clarity, convention, and Rails-native simplicity.
• Review: Inspect changes for unnecessary layers, non-RESTful design, anemic models, avoidable client-side complexity, and departures from the conventions below.

For reviews, report concrete deviations, explain the simpler Rails-native alternative, and finish with APPROVED or NEEDS CHANGES. Do not pad the review with praise.

Quick Reference

Controller Actions

• Only 7 REST actions: index, show, new, create, edit, update, destroy
• New behavior? Create a new controller, not a custom action
• Action length: 1-5 lines maximum
• Empty actions are fine: Let Rails convention handle rendering

class MessagesController < ApplicationController
  before_action :set_message, only: %i[ show edit update destroy ]

  def index
    @messages = @room.messages.with_creator.last_page
    fresh_when @messages
  end

  def show
  end

  def create
    @message = @room.messages.create_with_attachment!(message_params)
    @message.broadcast_create
  end

  private
    def set_message
      @message = @room.messages.find(params[:id])
    end

    def message_params
      params.require(:message).permit(:body, :attachment)
    end
end

Private Method Indentation

Indent private methods one level under private keyword:

  private
    def set_message
      @message = Message.find(params[:id])
    end

    def message_params
      params.require(:message).permit(:body)
    end

Model Design (Fat Models)

Models own business logic, authorization, and broadcasting:

class Message < ApplicationRecord
  belongs_to :room
  belongs_to :creator, class_name: "User"
  has_many :mentions

  scope :with_creator, -> { includes(:creator) }
  scope :page_before, ->(cursor) { where("id < ?", cursor.id).order(id: :desc).limit(50) }

  def broadcast_create
    broadcast_append_to room, :messages, target: "messages"
  end

  def mentionees
    mentions.includes(:user).map(&:user)
  end
end

class User < ApplicationRecord
  def can_administer?(message)
    message.creator == self || admin?
  end
end

Current Attributes

Use Current for request context, never pass current_user everywhere:

class Current < ActiveSupport::CurrentAttributes
  attribute :user, :session
end

# Usage anywhere in app
Current.user.can_administer?(@message)

Ruby Syntax Preferences

DHH-specific style (for general Ruby style, see ruby-coder skill):

# Symbol arrays with spaces inside brackets
before_action :set_message, only: %i[ show edit update destroy ]

# Expression-less case for cleaner conditionals
case
when params[:before].present?
  @room.messages.page_before(params[:before])
when params[:after].present?
  @room.messages.page_after(params[:after])
else
  @room.messages.last_page
end

Query Optimization

Prefer pluck(:name) over map(&:name) and messages.count over messages.to_a.count -- push work to the database.

StringInquirer for Predicates

Use .inquiry on string enums for readable conditionals:

class Event < ApplicationRecord
  def action
    super.inquiry
  end
end

# Clean predicate methods
event.action.completed?
event.action.pending?
event.action.failed?

Controller Response Patterns

Use head :no_content for updates without body, head :created for creates. Bang methods (create!, update!) for fail-fast.

My:: Namespace for Current User Resources

Use My:: namespace for resources scoped to Current.user:

# routes.rb
namespace :my do
  resource :profile, only: %i[ show edit update ]
  resources :notifications, only: %i[ index destroy ]
end

# app/controllers/my/profiles_controller.rb
class My::ProfilesController < ApplicationController
  def show
    @profile = Current.user
  end
end

No index or show with ID needed. The resource is implicit from Current.user.

Compute at Write Time

Perform data manipulation during saves, not during presentation:

# WRONG: Compute on read
def display_name
  "#{first_name} #{last_name}".titleize
end

# CORRECT: Compute on write
before_save :set_display_name

private
  def set_display_name
    self.display_name = "#{first_name} #{last_name}".titleize
  end

Benefits: enables pagination, caching, and reduces view complexity.

Delegate for Lazy Loading

Use delegate to enable lazy loading through associations:

class Message < ApplicationRecord
  belongs_to :session
  delegate :user, to: :session
end

# Lazy loads user through session
message.user

Naming Conventions

Hotwire/Turbo Patterns

Broadcasting is model responsibility:

# In model
def broadcast_create
  broadcast_append_to room, :messages, target: "messages"
end

For detailed Hotwire patterns, use hotwire-coder skill.

Error Handling

Rescue specific exceptions, fail fast with bang methods:

def create
  @message = @room.messages.create_with_attachment!(message_params)
  @message.broadcast_create
rescue ActiveRecord::RecordNotFound
  render action: :room_not_found
end

State as Records (Not Booleans)

Track state via database records rather than boolean columns:

# WRONG: Boolean columns for state
class Card < ApplicationRecord
  # closed: boolean, gilded: boolean columns
end
card.update!(closed: true)
card.closed?  # Loses who/when/why

# CORRECT: State as separate records
class Card < ApplicationRecord
  has_one :closure
  has_one :gilding

  def close(by:)
    create_closure!(closed_by: by)
  end

  def closed?
    closure.present?
  end
end
card.close(by: Current.user)
card.closure.closed_by  # Full audit trail

REST URL Transformations

Map custom actions to nested resource controllers:

# routes.rb
resources :cards do
  resource :closure, only: %i[ create destroy ]
  resource :gilding, only: %i[ create destroy ]
end

# app/controllers/cards/closures_controller.rb
class Cards::ClosuresController < ApplicationController
  def create
    @card = Card.find(params[:card_id])
    @card.close(by: Current.user)
  end

  def destroy
    @card = Card.find(params[:card_id])
    @card.closure.destroy!
  end
end

Detailed Reference

Load detailed-reference.md for extended examples, templates, and advanced patterns.