Chapter 10. Aggregates

The universe is built up into an aggregate of permanent objects connected by causal relations that are independent of the subject and are placed in objective space and time.

—Jean Piaget

Clustering Entities (5) and Value Objects (6) into an Aggregate with a carefully crafted consistency boundary may at first seem like quick work, but among all DDD tactical guidance, this pattern is one of the least well understood.

Road Map to This Chapter

• Along with SaaSOvation, experience the negative consequences of improperly modeling Aggregates.

• Learn to design by the Aggregate Rules of Thumb as a set of best-practice guidelines.

• Grasp how to model true invariants in consistency boundaries according to real business rules.

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