model patterns

SKILL.md

Expert decision frameworks for model design choices. Claude knows Codable syntax — this skill provides judgment calls for when to separate DTOs, validation strategies, and immutability trade-offs.

The trap: DTO for everything. If your API matches your domain and is stable, a single Codable struct is simpler. Add DTO layer when it solves a real problem.

| API matches domain exactly | No | | API likely to change | Yes | | Need transformation (flatten, combine) | Yes | | Multiple APIs for same concept | Yes | | Single stable internal API | No |

Expert model design decisions for iOS/tvOS: when DTO separation adds value vs overkill, validation strategy selection, immutability trade-offs, and custom Codable decoder design. Use when designing data models, implementing API contracts, or debugging decoding failures. Trigger keywords: Codable, DTO, domain model, CodingKeys, custom decoder, validation, immutable, struct, mapping, JSON decoding Source: kaakati/rails-enterprise-dev.

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