Layered Rails

Design and review Rails applications using layered architecture principles.

Quick Start

Rails applications are organized into four architecture layers with unidirectional data flow:

┌─────────────────────────────────────────┐
│           PRESENTATION LAYER            │
│  Controllers, Views, Channels, Mailers  │
└─────────────────────────────────────────┘
                    ↓
┌─────────────────────────────────────────┐
│           APPLICATION LAYER             │
│   Service Objects, Form Objects, etc.   │
└─────────────────────────────────────────┘
                    ↓
┌─────────────────────────────────────────┐
│             DOMAIN LAYER                │
│  Models, Value Objects, Domain Events   │
└─────────────────────────────────────────┘
                    ↓
┌─────────────────────────────────────────┐
│          INFRASTRUCTURE LAYER           │
│  Active Record, APIs, File Storage      │
└─────────────────────────────────────────┘

Core Rule: Lower layers must never depend on higher layers.

What Would You Like To Do?

1. •Analyze codebase - Run /layers:analyze for full analysis or /layers:analyze:callbacks, /layers:analyze:gods for specific checks
2. •Review code changes - Run /layers:review for layered architecture review
3. •Run specification test - Run /layers:spec-test on specific files
4. •Plan gradual adoption - Run /layers:gradual [goal] to plan incremental layerification
5. •Plan feature implementation - I'll guide you using layered principles
6. •Implement specific pattern - I'll help with authorization, notifications, view components, AI integration, etc.

Core Principles

The Four Rules

1. •Unidirectional Data Flow - Data flows top-to-bottom only
2. •No Reverse Dependencies - Lower layers never depend on higher layers
3. •Abstraction Boundaries - Each abstraction belongs to exactly one layer
4. •Minimize Connections - Fewer inter-layer connections = looser coupling

Common Violations

See Anti-Patterns Reference for complete list.

The Specification Test

If the specification of an object describes features beyond the primary responsibility of its abstraction layer, such features should be extracted into lower layers.

How to apply:

1. •List responsibilities the code handles
2. •Evaluate each against the layer's primary concern
3. •Extract misplaced responsibilities to appropriate layers

See Specification Test Reference for detailed guide.

Pattern Catalog

Pattern Selection Guide

"Where should this code go?"

Remember: Services are a "waiting room" for code until proper abstractions emerge. Don't let app/services become a bag of random objects.

Commands Reference

Topic References

For deep dives on specific topics:

Gem References

For library-specific guidance:

Extraction Signals

When to extract from models:

Callback Scoring:

See Extraction Signals Reference for detailed guide.

Model Organization

Recommended order within model files:

class User < ApplicationRecord
  # 1. Gems/DSL extensions
  has_secure_password

  # 2. Associations
  belongs_to :account
  has_many :posts

  # 3. Enums
  enum :status, { pending: 0, active: 1 }

  # 4. Normalization
  normalizes :email, with: -> { _1.strip.downcase }

  # 5. Validations
  validates :email, presence: true

  # 6. Scopes
  scope :active, -> { where(status: :active) }

  # 7. Callbacks (transformers only)
  before_validation :set_defaults

  # 8. Delegations
  delegate :name, to: :account, prefix: true

  # 9. Public methods
  def full_name = "#{first_name} #{last_name}"

  # 10. Private methods
  private

  def set_defaults
    self.locale ||= I18n.default_locale
  end
end

Success Checklist

Well-layered code:

• • No reverse dependencies (lower layers don't depend on higher)
• • Models don't access Current attributes
• • Services don't accept request objects
• • Controllers are thin (HTTP concerns only)
• • Domain logic lives in models, not services
• • Callbacks score 4+ or are extracted
• • Concerns are behavioral, not code-slicing
• • Abstractions don't span multiple layers
• • Tests verify appropriate layer responsibilities

Guidelines

• •Use domain language - Name models after business concepts (Participant, not User; Cloud, not GeneratedImage)
• •Patterns before abstractions - Let code age before extracting; premature abstraction is worse than duplication
• •Services as waiting room - Don't let app/services become permanent residence for code
• •Explicit over implicit - Prefer explicit parameters over Current attributes
• •Extraction thresholds - Consider extraction when methods exceed 15 lines or call external APIs