DDD Aggregate Design

An aggregate is a consistency boundary. Design it around true invariants, not object graphs, database tables, or UI screens.

Workflow

1. Name the command and business invariant under discussion.

2. Decide what must be strongly consistent immediately. Put only that inside one aggregate.

3. Choose one aggregate root as the only external entry point.

4. Reference other aggregates by ID and coordinate them with events, policies, sagas, or process managers.

5. Prefer immutable updates unless the language or framework strongly pushes otherwise.

6. Review constructors/factories for complete initialization and invariant protection.

Core Rules