DDD Rails Modeling

Use this skill when the domain concepts are clear enough that the next question is how to model them in Rails.

Core principle: Model real domain pressure, not textbook DDD vocabulary.

Quick Reference

Concept	Rails-first default
Entity	ActiveRecord model when persisted identity matters
Value object	Plain Ruby object near the domain it supports
Aggregate root	The main entry point that guards invariants
Domain service	PORO for business behavior that does not belong to one entity
Application service	Orchestrator in `app/services` coordinating a use case
Repository	Use only for a real boundary beyond normal ActiveRecord usage
Domain event	Explicit object only when multiple downstream consumers justify it

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