Rails Implementation

Overview

This skill provides comprehensive support for Rails development, including:

• Feature implementation with Rails best practices
• Test creation (RSpec/Minitest) with meaningful coverage
• Code quality maintenance to prevent bloated classes and methods
• Common pattern implementation (CRUD, authentication, APIs, etc.)

Development Workflow

Follow this workflow when implementing Rails features:

1. Understand the Request

• Clarify requirements if ambiguous
• Identify which models, controllers, and views are affected
• Determine if new migrations are needed

2. Detect Project Configuration

Before implementation, identify:

Test Framework:

# Check for RSpec
ls spec/

# Check for Minitest
ls test/

Rails Version:

cat Gemfile | grep "rails"

Database:

cat config/database.yml

3. Plan the Implementation

Consider:

• Scope: Keep methods under 15 lines, classes focused
• Patterns: Use service objects, query objects, form objects when appropriate
• Testing: Plan meaningful tests (avoid testing constants, simple accessors)
• References: Check rails-patterns.md for common patterns

4. Implement

Code Quality Standards:

• ✅ Methods: 5-10 lines (max 15)
• ✅ Controllers: Max 7 RESTful actions
• ✅ Models: Max 20 public methods
• ✅ Nesting: Max 2-3 levels (use early returns)
• ✅ Single Responsibility: One purpose per class/method

When to Extract:

• Service Objects: Complex business logic, multi-step processes
• Query Objects: Complex database queries
• Form Objects: Multi-model forms
• Decorators: Presentation logic

For detailed patterns and examples, see code-quality.md.

After Model Changes (if annotate gem exists):

When creating or modifying models:

1. Run migrations: rails db:migrate
2. Check for annotate gem: bundle list | grep annotate
3. If annotate exists, run: bundle exec annotate
4. Add meaningful descriptions to columns in the generated annotations

See rails-patterns.md → Model Annotations for details.

5. Write Tests

Test Strategy:

Tests are mandatory but should be meaningful.

✅ DO Test:

• Custom business logic and methods
• Complex validations with custom logic
• Controller actions (request specs preferred)
• Service objects and POROs
• Scopes with complex logic
• Callbacks with side effects

❌ DON'T Test:

• Constant values
• Simple attribute accessors
• Framework features (Rails validations/associations without custom logic)
• Private methods directly
• Database schema

Test Framework Patterns:

See testing-guide.md for detailed examples covering:

• RSpec model, controller, and request specs
• Minitest model, controller, and system tests
• What to test and what to avoid

6. Update Documentation (If Needed)

Update documentation only when:

• Adding new API endpoints
• Changing public interfaces
• Adding complex features requiring explanation
• Modifying setup/deployment procedures

Common Implementation Patterns

For quick reference, common patterns include:

Model Annotations - Adding schema information with meaningful column descriptions using annotate gem

CRUD Operations - Basic resource implementation with model, controller, views

Authentication - Devise integration or custom authentication

API Endpoints - JSON API with proper status codes and error handling

Background Jobs - Active Job for asynchronous processing

File Uploads - Active Storage for attachments

Search & Filtering - Scopes and query objects for data retrieval

Associations - has_many, belongs_to, has_many :through, polymorphic

For detailed implementation examples, see rails-patterns.md.

Testing Strategy

Test-Driven Development (TDD)

TDD is recommended but not mandatory. The workflow is:

1. Red: Write failing test
2. Green: Minimal implementation to pass
3. Refactor: Improve code while keeping tests green

Whether writing tests first or after implementation, tests are mandatory for all custom logic.

Test Coverage Priorities

High Priority:

1. Business logic and custom methods
2. Service objects
3. Controller actions (happy path + error cases)
4. Complex validations

Low Priority:

• Simple CRUD without custom logic
• Framework features

Never Test:

• Constants, accessors, schema, framework validations (see testing-guide.md)

Code Quality Checkpoints

Before considering implementation complete, verify:

• [ ] No methods exceed 15 lines
• [ ] No deep nesting (max 2-3 levels)
• [ ] Controllers have max 7 actions
• [ ] Models have max 20 public methods
• [ ] Complex logic extracted to service/query/form objects
• [ ] All custom logic has meaningful tests
• [ ] No useless tests (constants, simple accessors)

If any checkpoint fails, refactor before proceeding.

References

This skill includes detailed reference documentation:

rails-patterns.md

Common Rails implementation patterns with code examples:

• CRUD operations
• Authentication & Authorization
• API endpoints
• Background jobs
• File uploads
• Search & filtering
• Associations

When to read: When implementing a feature and need a pattern reference.

testing-guide.md

Comprehensive testing guide with RSpec and Minitest examples:

• What to test vs. what NOT to test
• Model, controller, and request test examples
• System tests
• Avoiding meaningless tests

When to read: When writing tests or unsure if a test is meaningful.

code-quality.md

Code quality guidelines and refactoring patterns:

• Method and class size limits
• Service objects, query objects, form objects, decorators
• Refactoring patterns
• Early returns and extract method

When to read: When code feels bloated or before committing large changes.

Quick Start Examples

Example 1: Add "Like" Feature to Articles

Request: "Add a like feature to articles"

Workflow:

1. Create Like model with migration
2. Run rails db:migrate
3. If annotate gem exists: Run bundle exec annotate and add column descriptions
4. Add associations (Article has_many :likes, User has_many :likes)
5. Create LikesController with create and destroy actions
6. Add routes (resources :articles { resources :likes, only: [:create, :destroy] })
7. Write tests for model associations and controller actions
8. Add UI button in article view

Check: Methods stay under 15 lines, tests cover like/unlike behavior, annotations updated.

Example 2: Create API Endpoint for Articles

Request: "Create API endpoint to list articles"

Workflow:

1. Create Api::V1::ArticlesController
2. Implement index action returning JSON
3. Add serializer if response needs custom formatting
4. Add routes under namespace :api { namespace :v1 { resources :articles } }
5. Write request specs testing JSON response and status codes

Reference: See rails-patterns.md → API Endpoints section

Example 3: Add Tests to Existing File

Request: "Add tests to app/models/article.rb"

Workflow:

1. Read app/models/article.rb to understand custom logic
2. Identify meaningful test cases (custom methods, validations, scopes)
3. Skip testing constants, accessors, basic associations
4. Write tests in spec/models/article_spec.rb (RSpec) or test/models/article_test.rb (Minitest)
5. Run tests to verify

Reference: See testing-guide.md → What to Test

Notes

• Language: Always respond in Japanese (日本語) per user's global settings
• TDD: Recommended but not mandatory; tests are always mandatory
• Git Operations: Only commit/push when explicitly requested
• Code Style: Follow existing project patterns and conventions