effigenix/bin/.claude/skills/ddd-model/rules/error-handling.md

Error Handling in DDD

This document defines error handling principles that apply across all layers and languages.

Core Principles

1. No Silent Failures - All errors must be explicitly handled or propagated
2. Layer-Specific Errors - Each layer defines its own error types
3. Error Transformation - Errors are transformed at layer boundaries
4. Proper Logging - Original errors logged before transformation
5. Result Types Over Exceptions - Prefer Result types (where supported) over exceptions

Language-Specific Implementation

• Java: See languages/java/error-handling.md
• Go: Use error returns and custom error types

Error Hierarchy

Domain Errors (business rule violations)
  ↓ transformed at boundary
Application Errors (use case failures)
  ↓ transformed at boundary  
Infrastructure Errors (technical failures)

Logging Strategy

• ERROR: Infrastructure failures (database down, network error)
• WARN: Business rule violations (insufficient funds, invalid state)
• INFO: Normal operations (order placed, account created)
• DEBUG: Detailed flow information
• TRACE: Original errors when transforming between layers

Exception Boundary

Infrastructure Layer is the exception boundary:

• Infrastructure catches external exceptions (SQL, HTTP, etc.)
• Transforms to domain error types
• Logs original exception at ERROR level
• Returns domain error type

Domain and Application layers:

• Never throw exceptions (use Result types or errors)
• Only work with domain/application error types
• No try/catch blocks needed