effigenix/.claude/skills/ddd-implement/README.md

DDD Implementation Skill

A Claude Code skill that acts as a Senior DDD Developer, implementing domain-driven code following Clean Architecture principles.

What This Skill Does

This skill helps you implement DDD code that follows established patterns and rules:

✅ Aggregates - With proper invariant enforcement and Result types ✅ Entities - Child entities within aggregates ✅ Value Objects - Immutable, self-validating ✅ Use Cases - In application layer with proper error handling ✅ Repositories - Interfaces in domain, implementations in infrastructure ✅ Domain Events - For cross-aggregate communication

When to Use This Skill

Use /ddd-implement when:

• You have a domain model designed (from /ddd-model)
• You need to implement specific aggregates, entities, or value objects
• You want code that follows DDD rules automatically
• You need proper error handling (Result types for Java, errors for Go)
• You want layer boundaries respected

Don't use this skill for:

• Domain modeling and design (use /ddd-model instead)
• Generic coding tasks (use default Claude Code)
• Non-DDD projects

Usage Examples

Implement an Aggregate

/ddd-implement --lang=java "Implement Order aggregate with addLineItem, removeLineItem, and cancel methods"

The skill will:

1. Create the aggregate in domain/order/
2. Add proper invariants (e.g., "Cannot modify cancelled order")
3. Use Result types for error handling
4. Implement sealed interfaces for errors
5. Add domain events (OrderCreated, OrderCancelled, etc.)

Implement a Use Case

/ddd-implement --lang=go "Implement PlaceOrder use case that creates an order and reserves inventory"

The skill will:

1. Create use case in application/order/
2. Use repository interfaces (not implementations)
3. Handle errors properly
4. Return DTOs (not domain objects)
5. Add transaction boundaries if needed

Implement a Repository

/ddd-implement --lang=java "Implement PostgreSQL repository for Order aggregate"

The skill will:

1. Create implementation in infrastructure/order/persistence/
2. Implement the domain interface
3. Add exception boundary (catch SQL exceptions → return domain errors)
4. Map between domain model and database schema

Implement from Existing File

/ddd-implement internal/domain/account/account.go

The skill will:

1. Detect language from file extension
2. Read existing code
3. Suggest improvements or complete partial implementations
4. Follow established patterns in the file

What Makes This Skill Different

Enforces DDD Rules Automatically

The skill knows and enforces:

• Aggregate boundaries (no direct aggregate-to-aggregate references)
• Invariant documentation and enforcement
• Entity equality (ID-based only)
• Value Object immutability
• Repository patterns (interface in domain, impl in infrastructure)
• Layer dependencies (domain has no external deps)

Language-Aware

For Java:

• Uses Result<E, T> types (no exceptions from domain/application)
• Uses sealed interfaces for errors
• Uses pattern matching with switch expressions
• Uses static imports for Failure/Success
• Follows Java 21+ conventions

For Go:

• Uses error return values
• Uses pointer receivers for aggregates/entities
• Uses value receivers for value objects
• Uses sentinel errors and custom error types
• Follows Uber Go Style Guide

Error Handling Built-In

The skill automatically:

• Returns Result types (Java) or errors (Go)
• Creates layer-specific error types
• Adds exception boundaries at infrastructure layer
• Logs errors appropriately (ERROR/WARN/INFO levels)
• Prevents silent failures

How It Works

1. Analyzes your request - Determines what to implement (aggregate, use case, etc.)
2. Detects language - From flags, file extensions, or project structure
3. Loads rules - DDD rules, error handling, style guides for your language
4. Generates code - Following templates and patterns
5. Validates - Checks against DDD rules before completion

Architecture

/ddd-implement
├── SKILL.md              # Skill manifest (loaded by Claude Code)
├── system-prompt.md      # Core instructions for the implementation agent
├── README.md             # This file
└── examples/
    ├── go-example.md     # Example session in Go
    └── java-example.md   # Example session in Java

The system-prompt.md references rules from the ddd-model skill:

• ddd-model/rules/ddd-rules.md - Core DDD patterns
• ddd-model/rules/error-handling.md - Error handling strategy
• ddd-model/languages/{lang}/style-guide.md - Language conventions
• ddd-model/languages/{lang}/templates/ - Code templates

Workflow: Modeling → Implementation

1. Design with /ddd-model
   ↓ (identifies aggregates, entities, invariants)

2. Implement with /ddd-implement
   ↓ (generates code following rules)

3. Review with /review (or code review)
   ↓ (validates DDD principles)

4. Iterate

Examples

See detailed examples in:

• Java Example Session
• Go Example Session

Rules Reference

This skill enforces rules from:

• DDD Rules: ddd-model/rules/ddd-rules.md
• Clean Architecture: ddd-model/rules/clean-arch.md
• Error Handling: ddd-model/rules/error-handling.md
• Java Style: ddd-model/languages/java/style-guide.md
• Go Style: ddd-model/languages/go/style-guide.md

Contributing

To improve this skill:

1. Add examples - Real-world implementation sessions in examples/
2. Refine rules - Update system-prompt.md based on experience
3. Add templates - Language-specific templates in ddd-model/languages/{lang}/templates/
4. Document patterns - Special patterns in ddd-model/rules/

Related Skills

• ddd-model - For domain modeling and design
• review - For code review with DDD principles (if available)