Implementing Domain-Driven Design

Making Aggregates Work Together through Identity References

Prefer references to external Aggregates only by their globally unique identity, not by holding a direct object reference (or “pointer”). This is exemplified in Figure 10.6.

Figure 10.6. The BacklogItem Aggregate, inferring associations outside its boundary with identities

We would refactor the source to

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public class BacklogItem extends ConcurrencySafeEntity  {     ...     private ProductId productId;     ... }

Aggregates with inferred object references are thus automatically smaller because references are never eagerly loaded. The model can perform better ...