backend-code-organisation

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name: backend-code-organisation description: Kotlin backend layering and packaging guidelines license: MIT

Mission

• Keep backend services modular: resources handle transport, managers own business logic, and data access stays isolated.
• Maintain clean dependency flow across modules (service → core → models) to encourage reuse and testability.

Layering Principles

• Resources: Only translate HTTP/storage inputs to domain calls. No database or cross-service logic. Convert SecurityContext early.
• Managers: Encapsulate business rules; coordinate helpers, other managers, workflows, and DAL components. Break cycles by separating read/write responsibilities or introducing controllers.
• Helpers/Services: Reusable integrations (feature flags, external clients). Centralize external service calls to simplify retries and upgrades.
• Repos/DAL/DAO: Keep database interactions single-purpose. Compose multi-step transactions in repos/DAL; keep DAO calls single query.
• Utils/Validators/Transformers: Pure functions and extensions only; avoid hidden state.
• Cache Managers: Inject Redis/Lettuce clients, expose typed get/invalidate helpers.

Package & Module Structure

• Enforce lowercase package names without underscores; avoid versioned package hierarchies (v2 folders). Prefer managers.slots over managers.slots.v2.
• Organize by responsibility: managers, helpers, utils, dao, workflows, etc. Mirror structure in tests.
• Module boundaries:
  • core: managers, helpers, data access, transient models. May depend on models.
  • service: Dropwizard resources, configuration, application wiring; no direct DB access.
  • console-service: Console-specific resources/auth; depends on core.
  • client: Outbound clients; depend only on models.
  • models: Shared API/data contracts; no dependencies.

Dependency Injection & Config

• Add new Redis/Cosmos/DB configs across all environments (db-test, db-dev, db-warehouse-prod) and run the service locally to validate.
• Annotate injectable classes with @Singleton when appropriate.
• Only use @Named when multiple bindings of the same type exist; otherwise default bindings suffice.
• Centralize client construction in DI modules to enforce consistent timeouts and hosts.

Review Checklist

• Check that new features land in the correct layer and module (e.g., resources calling managers, not DAOs).
• Ensure helpers/managers do not introduce cyclic dependencies; suggest splitting read/write flows or using controller orchestrators.
• Verify repos/DAL enforce validation and error translation before returning data.
• Confirm new package or module names remain lowercase and idiomatic; flag attempts to create v2 package forks.
• Audit DI modules for duplicate provider methods and proper scoping.

Tooling Tips

• Glob for *.kt within service/ or core/ to inspect layer usage.
• Read DI modules when new bindings appear to ensure wiring matches guidelines.
• Grep for @Named or direct DAO usage inside resources to catch misplaced logic.