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?

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

Core Principles

The Four Rules

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

Common Violations

Violation	Example	Fix
Model uses Current	`Current.user` in model	Pass user as explicit parameter
Service accepts request	`param :request` in service	Extract value object from request
Controller has business logic	Pricing calculations in action	Extract to service or model
Anemic models	All logic in services	Keep domain logic in models

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:

List responsibilities the code handles
Evaluate each against the layer's primary concern
Extract misplaced responsibilities to appropriate layers

See Specification Test Reference for detailed guide.

Pattern Catalog

Pattern	Layer	Use When	Reference
Service Object	Application	Orchestrating domain operations	service-objects.md
Query Object	Domain	Complex, reusable queries	query-objects.md
Form Object	Presentation	Multi-model forms, complex validation	form-objects.md
Filter Object	Presentation	Request parameter transformation	filter-objects.md
Presenter	Presentation	View-specific logic, multiple models	presenters.md
Serializer	Presentation	API response formatting	serializers.md
Policy Object	Application	Authorization decisions	policy-objects.md
Value Object	Domain	Immutable, identity-less concepts	value-objects.md
State Machine	Domain	States, events, transitions	state-machines.md
Concern	Domain	Shared behavioral extraction	concerns.md

Pattern Selection Guide

"Where should this code go?"

If you have...	Consider...
Complex multi-model form	Form Object
Request parameter filtering/transformation	Filter Object
View-specific formatting	Presenter
Complex database query used in multiple places	Query Object
Business operation spanning multiple models	Service Object (as waiting room)
Authorization rules	Policy Object
Multi-channel notifications	Delivery Object (Active Delivery)

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

Command	Purpose
`/layers:review`	Review code changes from layered architecture perspective
`/layers:spec-test`	Run specification test on specific files
`/layers:analyze`	Full codebase abstraction layer analysis
`/layers:analyze:callbacks`	Score model callbacks, find extraction candidates
`/layers:analyze:gods`	Find God objects via churn × complexity
`/layers:gradual [goal]`	Plan gradual adoption of layered patterns

Topic References

For deep dives on specific topics:

Topic	Reference
Authorization (RBAC, ABAC, policies)	authorization.md
Notifications (multi-channel delivery)	notifications.md
View Components	view-components.md
AI Integration (LLM, agents, RAG, MCP)	ai-integration.md
Configuration	configuration.md
Callbacks (scoring, extraction)	callbacks.md
Current Attributes	current-attributes.md
Instrumentation (logging, metrics)	instrumentation.md

Gem References

For library-specific guidance:

Gem	Purpose	Reference
action_policy	Authorization framework	action-policy.md
view_component	Component framework	view-component.md
anyway_config	Typed configuration	anyway-config.md
active_delivery	Multi-channel notifications	active-delivery.md
alba	JSON serialization	alba.md
workflow	State machines	workflow.md
rubanok	Filter/transformation DSL	rubanok.md
active_agent	AI agent framework	active-agent.md
active_job-performs	Eliminate anemic jobs	active-job-performs.md

Extraction Signals

When to extract from models:

Signal	Metric	Action
God object	High churn × complexity	Decompose into concerns, delegates, or separate models
Operation callback	Score 1-2/5	Extract to service or event handler
Code-slicing concern	Groups by artifact type	Convert to behavioral concern or extract
Current dependency	Model reads Current.*	Pass as explicit parameter

Callback Scoring:

Type	Score	Keep?
Transformer (compute values)	5/5	Yes
Normalizer (sanitize input)	4/5	Yes
Utility (counter caches)	4/5	Yes
Observer (side effects)	2/5	Maybe
Operation (business steps)	1/5	Extract

See Extraction Signals Reference for detailed guide.

Model Organization

Recommended order within model files:

ruby

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

layered-rails

NPX Install

Tags

SKILL.md Content