DDD Types, State, And Mocks

Apply this pattern when one API resource maps to one entity slice. Use ddd-data-layer-advanced when one response hydrates several entities.

Source: Types, Initial State & Mocks

Place Files

domain/entity/<entity>/src/
├── schema.ts
├── schema.mock.ts
├── schema.test.ts
├── selectors.ts
├── selectors.test.ts
├── slice.ts
└── slice.test.ts

domain/api/<entity>/src/
├── api.ts
└── api.test.ts

Export only the contracts consumers need from each package index.ts.

Keep Ownership Clear

File	Responsibility
schema.ts	Define the runtime schema, infer the TypeScript type, and declare a complete initial state
schema.mock.ts	Build valid entity data with sensible defaults and optional overrides
slice.ts	Own focused entity reducers and actions
selectors.ts	Read or derive entity state without importing an app store type
api.ts	Own transport contracts, network calls, and transformations

Follow the package's runtime-schema precedent (Zod or Typia). Do not maintain a separate handwritten type that can drift from the schema.

Validate The Contract

• Give every entity property an explicit initial value.
• Make every mock pass the runtime schema.
• Keep mock-only helpers out of production behavior.
• Give reducers one clear state transition each.
• Parse untrusted API data before storing it when the API layer does not already guarantee the contract.
• Register reducers and API middleware in each app composition root; never import an app store from a domain package.

Test

• Schema: accept a mock, reject an invalid payload, and cover initial defaults.
• Mock: return valid data and honor supported overrides.
• Slice: cover initial state, replacement/reset, and focused updates.
• Selectors: cover direct and derived values with a minimal local state shape.
• API: cover success, relevant failures, and transformations with a local test store or existing domain test harness.