Methasit-Pun Simplify — TypeScript DDD
Three similar lines is better than a premature abstraction. Abstract only when a pattern has appeared in at least three real cases.
What to look for
Domain over-engineering
- VO wrapping a single
stringwith no validation or behavior — remove it (keep if it enforces format likeEmail,Money) - Aggregate that only delegates to a domain service for every operation — collapse the service into the aggregate
- Deeply nested event hierarchy (
DomainEvent → OrderEvent → OrderCancelledEvent) — flatten unless used for polymorphic handling
Application over-engineering
- Handler with one line
return this.repo.findById(id)— skip the use case, call the repo from the query handler directly - Command DTO with fields identical to the domain constructor params — collapse into one
- Interface with a single implementation that is never mocked in tests — inject the concrete class; add the interface when a second impl is needed
Infrastructure over-engineering
- Mapper that copies fields one-for-one with no type conversion — consider if domain and ORM models are actually the same thing at this stage
- Repository wrapping ORM with one-liner methods and no mapping or error handling — the layer adds no value yet
Premature patterns
| Pattern | Worth it when | Premature when |
|---|---|---|
| CQRS with separate read models | Queries are complex joins or aggregations | Simple CRUD reads |
| Event sourcing | Full audit trail or temporal queries required | Standard transactional state |
| Outbox pattern | Distributed at-least-once delivery needed | Single service, no message broker |
| Sagas / Process Managers | Multi-step multi-service long-running workflows | Single aggregate transitions |
What NOT to simplify
- Invariant-enforcing VOs even if they look like "just a string wrapper"
- Repository interface when it enables test doubles
- Domain events even if only one subscriber currently listens
- Mapper even if trivial — it protects the domain from ORM schema changes
Output format
Numbered list. Each finding: [REMOVE] / [COLLAPSE] / [DEFER] + file path + why it's safe to remove + what to do instead.