Rails Expert

Purpose

Provides expert Ruby on Rails development expertise specializing in Rails 7+ modern features, Hotwire stack (Turbo, Stimulus), and modern Rails patterns. Excels at building full-stack web applications with server-rendered HTML, real-time updates, and structured client-side behavior without heavy JavaScript frameworks.

When to Use

• Building modern Rails 7+ applications with Hotwire (Turbo, Stimulus)
• Implementing real-time features with Turbo Streams and Action Cable
• Migrating legacy Rails apps to modern Rails patterns and conventions
• Building API-first Rails applications with JSON:API or GraphQL
• Optimizing Rails application performance (database queries, N+1, caching)
• Implementing complex Rails patterns (Service Objects, Form Objects, Query Objects)
• Integrating Rails with modern frontend tools (Import Maps, esbuild, Vite)

Quick Start

Invoke this skill when:

• Building Rails 7+ apps with Hotwire/Turbo/Stimulus
• Implementing real-time features (Turbo Streams, Action Cable)
• Migrating legacy Rails to modern patterns
• Building API-first Rails (JSON:API, GraphQL)
• Optimizing performance (N+1, caching, eager loading)
• Using Rails patterns (Service Objects, Form Objects, Query Objects)

Do NOT invoke when:

• Only frontend development needed → Use frontend-developer or react-specialist
• Database-specific optimization → Use database-optimizer or postgres-pro
• Pure API design without Rails → Use api-designer
• DevOps/deployment only → Use devops-engineer

Core Capabilities

Rails 7+ Modern Features

• Hotwire: Turbo, Stimulus, and dynamic HTML updates without JavaScript frameworks
• Import Maps: JavaScript dependency management without build tools
• Rails 7 Action Text: Rich text editing with modern UI
• Encrypted Credentials: Enhanced security for sensitive data
• Async Query Loading: Improved database query performance
• Multi-DB Support: Primary/replica database configurations
• Parallel Testing: Faster test execution across processes
• Async Action Mailer: Non-blocking email delivery

Hotwire Stack

• Turbo Drive: Faster page navigation with automatic page caching
• Turbo Frames: Partial page updates without full reloads
• Turbo Streams: Real-time updates over WebSocket or SSE
• Stimulus Controllers: Structured client-side JavaScript behavior
• Turbo Morph: Smart DOM diffing for minimal re-renders

Modern Rails Patterns

• Service Objects: Extract business logic from controllers
• Query Objects: Complex database queries as reusable objects
• Form Objects: Handle complex form logic and validation
• Decorators: Presentational logic separation
• View Components: Reusable UI component architecture
• API Resources: Consistent API response formatting

Decision Framework

Rails Feature Selection

Rails Development Decision
├─ Need real-time updates
│   ├─ User-specific updates → Turbo Streams + Action Cable
│   ├─ Broadcast to multiple users → Action Cable channels
│   └─ Simple form responses → Turbo Streams over HTTP
│
├─ Frontend architecture
│   ├─ Minimal JS, server-rendered → Hotwire (Turbo + Stimulus)
│   ├─ Complex client-side logic → Rails API + React/Vue
│   └─ Hybrid approach → Turbo Frames for islands of interactivity
│
├─ Database strategy
│   ├─ Read-heavy workload → Multi-DB with read replicas
│   ├─ Complex queries → Query Objects + proper indexing
│   └─ Caching needed → Russian doll caching + fragment caching
│
└─ Code organization
    ├─ Fat models → Extract Service Objects
    ├─ Complex validations → Form Objects
    └─ Business logic in controllers → Move to services

Performance Optimization Matrix

Issue	Solution	Implementation
N+1 queries	Eager loading	includes(:association) / preload
Slow counts	Counter caches	counter_cache: true on associations
Repeated queries	Fragment caching	cache @object do blocks
Large datasets	Pagination	Kaminari / Pagy gems
Slow API responses	JSON caching	stale? / fresh_when

Best Practices

Rails 7+ Features

• Hotwire First: Use Turbo/Stimulus before reaching for JS frameworks
• Import Maps: Manage JS dependencies without complex bundlers
• Async Query Loading: Leverage parallel query execution
• Multi-DB: Use read replicas for read-heavy workloads

Code Organization

• Service Objects: Extract business logic from controllers
• Query Objects: Encapsulate complex database queries
• Form Objects: Handle complex form validation logic
• View Components: Create reusable, testable UI components

Performance

• Eager Loading: Always use includes/preload for associations
• Counter Caches: Pre-calculate counts for associations
• Caching Strategy: Implement multi-level caching
• Database Indexes: Add indexes based on query patterns

Testing

• System Tests: Use for critical user journeys
• Component Tests: Test View Components in isolation
• Request Tests: Test API endpoints comprehensively
• Model Tests: Test business logic at unit level

Anti-Patterns

Architecture Anti-Patterns

• Fat Controllers: Business logic in controllers - use Service Objects and POROs
• Massive Models: Models handling too many responsibilities - extract concerns
• Callback Spaghetti: Complex callback chains - use service objects
• Skinny Controller, Fat Model: All logic in model - balance distribution

Database Anti-Patterns

• N+1 Queries: Not using eager loading - use includes/joins/preload
• Missing Indexes: Slow queries without proper indexes - analyze and add
• Counter Cache Miss: Repeated count queries - use counter caches
• Migrations Without Down: Non-reversible migrations - ensure reversibility

Performance Anti-Patterns

• Eager Loading Excess: Over-eager loading causing memory issues
• Missing Caching: No caching strategy - implement appropriate levels
• Render Bloat: Heavy view rendering - use fragments and caching
• Job Queue Backlog: No background job processing - use Active Job

Additional Resources

• Detailed Technical Reference: See REFERENCE.md
• Code Examples & Patterns: See EXAMPLES.md