dhh-coder

name	dhh-coder
description	Write Ruby and Rails code in DHH's distinctive 37signals style. Use this skill when writing Ruby code, Rails applications, creating models, controllers, or any Ruby file. Triggers on Ruby/Rails code generation, refactoring requests, or when the user mentions DHH, 37signals, Basecamp, HEY, Fizzy, or Campfire style.

DHH Ruby/Rails Style Guide

Write Ruby and Rails code following DHH's philosophy: clarity over cleverness, convention over configuration, developer happiness above all.

Patterns derived from 37signals' production applications: Basecamp, HEY, Campfire, and the open-source Fizzy SaaS project.

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

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

# Modern hash syntax exclusively
params.require(:message).permit(:body, :attachment)

# Single-line blocks with braces
users.each { |user| user.notify }

# Ternaries for simple conditionals
@room.direct? ? @room.users : @message.mentionees

# Bang methods for fail-fast
@message = Message.create!(params)
@message.update!(message_params)

# Predicate methods with question marks
@room.direct?
user.can_administer?(@message)
@messages.any?

# 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

Naming Conventions

Element	Convention	Example
Setter methods	set_ prefix	set_message, set_room
Parameter methods	{model}_params	message_params
Association names	Semantic, not generic	creator not user
Scopes	Chainable, descriptive	with_creator, page_before
Predicates	End with ?	direct?, can_administer?

Hotwire/Turbo Patterns

Broadcasting is model responsibility:

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

# In controller
@message.broadcast_replace_to @room, :messages,
  target: [ @message, :presentation ],
  partial: "messages/presentation",
  attributes: { maintain_scroll: true }

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

Architecture Preferences

Traditional	DHH Way
PostgreSQL	SQLite (for single-tenant)
Redis + Sidekiq	Solid Queue
Redis cache	Solid Cache
Kubernetes	Single Docker container
Service objects	Fat models
Policy objects (Pundit)	Authorization on User model
FactoryBot	Fixtures

Detailed References

For comprehensive patterns and examples, see:

Core Patterns

• references/patterns.md - Complete code patterns with explanations
• references/palkan-patterns.md - Namespaced model classes, counter caches, model organization order, PostgreSQL enums
• references/concerns-organization.md - Model-specific vs common concerns, facade pattern
• references/delegated-types.md - Polymorphism without STI problems
• references/recording-pattern.md - Unifying abstraction for diverse content types
• references/filter-objects.md - PORO filter objects, URL-based state, testable query building

Rails Components

• references/activerecord-tips.md - ActiveRecord query patterns, validations, associations
• references/controllers-tips.md - Controller patterns, routing, rate limiting, form objects
• references/hotwire-tips.md - Turbo Frames, Turbo Streams, Stimulus, ViewComponents
• references/turbo-morphing.md - Turbo 8 page refresh with morphing patterns
• references/activestorage-tips.md - File uploads, attachments, blob handling
• references/stimulus-catalog.md - Copy-paste-ready Stimulus controllers (clipboard, dialog, hotkey, etc.)

Frontend

• references/css-architecture.md - Native CSS patterns (layers, OKLCH, nesting, dark mode)

Authentication & Multi-Tenancy

• references/passwordless-auth.md - Magic link authentication, sessions, identity model
• references/multi-tenancy.md - Path-based tenancy, cookie scoping, tenant-aware jobs

Infrastructure & Integrations

• references/webhooks.md - Secure webhook delivery, SSRF protection, retry strategies
• references/caching-strategies.md - Russian Doll caching, Solid Cache, cache analysis
• references/config-tips.md - Configuration, logging, deployment patterns
• references/resources.md - Links to source material and further reading

Philosophy Summary

1. REST purity: 7 actions only; new controllers for variations
2. Fat models: Authorization, broadcasting, business logic in models
3. Thin controllers: 1-5 line actions; extract complexity
4. Convention over configuration: Empty methods, implicit rendering
5. Minimal abstractions: No service objects for simple cases
6. Current attributes: Thread-local request context everywhere
7. Hotwire-first: Model-level broadcasting, Turbo Streams, Stimulus
8. Readable code: Semantic naming, small methods, no comments needed