ca-kotlin

name

ca-kotlin

description

Clean Architecture rules and patterns for Kotlin + Spring Boot + Arrow-kt projects. Use when implementing or reviewing any CA layer: domain modeling, use case design, repository patterns, infrastructure implementation, or controller/DataFetcher wiring. Triggers on: domain entity design, value object creation, repository interface definition, use case implementation, jOOQ repository, REST controller, DGS DataFetcher, DI wiring.

Clean Architecture — Kotlin

Layer Dependency Direction

framework → presentation → application → domain ← infrastructure

CQRS Pattern

The application layer is split into command/ (writes) and query/ (reads):

• Command side: application/command/ → uses domain repository (in domain/) → returns domain entities
• Query side: application/query/ → uses query repository (in application/query/repository/) → returns flat DTOs

Key Patterns

Concept	Pattern
Entity	data class Entity(val id: EntityId, ...) — val only, .copy() for updates
Value Object	@JvmInline value class VO private constructor(val value: T) with of() returning Either
Domain Error	sealed interface XxxError : DomainError
Domain Repo Interface	In domain/, write methods only (save, delete), returns Either<XxxError, T>
Command Use Case	interface XxxSaveUseCase in application/command/ — uses domain repository
Query Repo Interface	In application/query/repository/, read methods, returns Either<QueryError, QueryDto>
Query Use Case	interface XxxListQueryUseCase in application/query/ — uses query repository
Query DTO	data class XxxQueryDto(val id: Long, ...) — flat primitives, no domain types
Infra Domain Repo	@Repository class XxxRepositoryImpl(dsl: DSLContext) in infrastructure/command/repository/
Infra Query Repo	@Repository class XxxQueryRepositoryImpl(dsl: DSLContext) in infrastructure/query/repository/
REST Controller	@RestController injecting both command and query use cases
GraphQL DataFetcher	@DgsComponent injecting both command and query use cases
DI Wiring	@Bean for both command use cases (domain repo) and query use cases (query repo)

Forbidden Imports by Layer

Layer	Forbidden
domain	org.springframework.*, jakarta.*, *.application.*, *.infrastructure.*, jOOQ
application	Same as domain + no infra/presentation imports
presentation	*.infrastructure.* only (may import *.domain.* for DTO mapping)

Strict Rules

• NO throw in domain/application/infrastructure — use Either
• NO @Component/@Service on use case classes — wire manually via @Bean
• NO new library deps in domain or application build.gradle.kts

This project uses jOOQ + R2DBC (NOT JPA). See references/layer-rules.md for detailed layer implementation examples. For Arrow-kt API patterns (either{}, .bind(), mapLeft, Either.catch, .fold()): see the arrow-kt skill.