Rails Expert

---
name: Rails Expert
description: Use when building full-stack Rails 7+ applications with Hotwire, ActiveRecord patterns, Turbo, and Stimulus.
category: Languages
version: 1.0.0
tools: []
---

# Rails 7+ Development

Build applications using Rails 7+ conventions, Hotwire for interactivity, and ActiveRecord patterns that scale.

## Core Principles

- Follow Rails conventions; if fighting the framework, reconsider the approach
- Use Hotwire first: Turbo and Stimulus before reaching for JavaScript frameworks
- Keep models focused on associations, validations, scopes; extract business logic to service objects
- Every foreign key and `WHERE` column gets an index; database indexes are not optional

## Project Conventions

```
app/
  controllers/    # Thin controllers, one action per concern
  models/         # ActiveRecord models, validations, scopes
  services/       # Business logic (PlaceOrderService, SendNotificationService)
  queries/        # Complex query objects
  views/          # ERB templates with Turbo Frames
  components/     # ViewComponent classes for reusable UI
  jobs/           # ActiveJob background processors
```

## ActiveRecord Patterns

- Use scopes for reusable query fragments: `scope :active, -> { where(status: :active) }`
- Use `has_many :through` for many-to-many relationships; avoid `has_and_belongs_to_many`
- Use `counter_cache: true` on `belongs_to` for frequently counted associations
- Use `find_each` or `in_batches` for large datasets; never load entire tables
- Enable `config.active_record.strict_loading_by_default` to catch N+1 queries in development
- Use `strong_migrations` gem; verify safety before using `safety_assured` blocks

## Hotwire Stack

- Use Turbo Drive for SPA-like navigation without JavaScript
- Use Turbo Frames to update specific page sections: `<turbo-frame id="user_profile">`
- Use Turbo Streams for real-time updates: `broadcast_append_to`, `broadcast_replace_to`
- Use Stimulus for small JavaScript behaviors: toggles, form validation, clipboard copy
- Use `turbo_stream.erb` response templates for multi-target updates

## Background Jobs & Testing

- Use Sidekiq with Redis for background processing; configure `config.active_job.queue_adapter = :sidekiq`
- Make every job idempotent; design for at-least-once execution
- Use separate queues: `default`, `mailers`, `critical`, `low_priority`
- Set `retry: 5` with exponential backoff; move to dead letter queue after exhaustion
- Use RSpec with `factory_bot` and `shoulda-matchers`
- Use `VCR` or `WebMock` for external HTTP mocking; never hit real APIs in tests
- Use `DatabaseCleaner` with transaction strategy for speed

## Performance & Security

- Use `includes` for eager-loading; use `bullet` gem to detect N+1 queries
- Cache view fragments: `cache [user, user.updated_at]` with `touch: true`
- Use `Rails.cache.fetch` for expensive computations
- Profile with `rack-mini-profiler` and `memory_profiler` gems
- Run `bundle exec brakeman` for security vulnerability scanning

## Before Completing

- Run `bundle exec rspec` to verify specs pass
- Run `bundle exec rubocop` for code style compliance
- Run `bin/rails db:migrate:status` to verify migration state
- Run `bundle exec brakeman` for security scanning