DDD Cross-Aggregate Constraints

A cross-aggregate constraint is usually a requirements question before it is a technical question.

Workflow

1. Restate the rule in business language and ask whether it must be immediately true.

2. If it is a true invariant, consider merging the aggregate boundary or changing the command owner.

3. If it is a policy, use events, reservations, or compensating actions; use a saga only for multi-step orchestration and compensation, not for synchronous existence checks.

4. In CQRS/ES, avoid command decisions based on stale read models unless the business accepts that staleness.

5. Document the inconsistency window and repair mechanism.

Decision Options

• Same aggregate: use when the rule is a true invariant.