service

Define the contract as an abstract class so tsyringe can use it as a DI token, then create an @injectable() concrete implementation extending it. Bind both mock and real implementations through the INSTANCE_REGISTRY in the owning context's registry.ts file.

Use a service when logic spans multiple aggregates, calls external APIs, or coordinates infrastructure like storage or email. Keep logic on the entity when it only involves that entity's own data and invariants.

No. An interface is only justified when multiple implementations exist or are planned, such as a stub for development and a real implementation for production. With a single permanent implementation, provide the concrete struct directly.

Register context-local services in the context's module.go using fx.Provide, and use fx.As(new(FooService)) when consumers depend on the interface. Cross-context infrastructure services are wired at the application root in cmd/api/main.go.

When concrete implementations are injected into a factory by their concrete type rather than an abstract token, tsyringe auto-resolves them with only @injectable(). No INSTANCE_REGISTRY entries are needed for the factory or its implementations.

Services must hold no database driver and run no queries; persistence belongs to repositories. A service composes repository ports and threads an optional transaction parameter through repository calls while the use case owns the transaction boundary.