Aggregate
An aggregate is a cluster of related domain objects treated as a single consistency and modification boundary.
Collaborative Software Design: How to facilitate domain modeling decisions
A consistency boundary is a boundary within which related state must satisfy business invariants as a single consistent unit.
- How it is used
- Uses aggregates to turn collaborative modeling constraints into implementable boundaries that preserve business invariants.
- How deep it goes
- Explains boundaries, transactions, aggregate roots, and invariant enforcement, then stops short of a complete implementation.
- Examples
- Uses seat allocation, scheduled movies, tickets, rows, and a simplified ScheduledMovie aggregate to illustrate invariant enforcement.
- What you can do after
- Builds aggregate boundaries and methods from modeled constraints while keeping related domain objects internally consistent.
Simple Object-Oriented Design: Create clean, maintainable applications
An aggregate is a cluster of related domain objects treated as a consistency boundary and accessed through a designated root.
- How it is used
- Defines a consistency boundary for clusters of domain objects and their persistence.
- How deep it goes
- Explains root-only access, repository boundaries, and a worked Offering–Enrollment design; defers deeper aggregate-root design.
- Examples
- Uses Basket–Item–Product and Offering–Enrollment relationships, including enrollment cancellation and available spots.
- What you can do after
- Apply it by routing related changes and persistence through an aggregate root while evaluating exceptions pragmatically.
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Spring in Action, Sixth Edition
An aggregate is a domain-driven design cluster of related objects treated as a unit for consistency and lifecycle management.
- How it is used
- Organizes domain objects and directs repository operations around an aggregate root.
- How deep it goes
- Defines membership and demonstrates multi-table saving, but defers broader domain-driven design beyond aggregates and roots.
- Examples
- Uses TacoOrder, Taco, Ingredient, IngredientRef, SQL tables, and a JdbcOrderRepository save operation.
- What you can do after
- Build it from scratch by defining an aggregate root, repository, schema relationships, and coordinated JDBC persistence.
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Related concepts
- domain eventproduces · A domain event is a record of a significant occurrence or state change in a business domain that may be relevant to subsequent behavior or decisions.
- business invariantaddresses · A business invariant is a condition that must remain true for a domain model to represent a valid business state.
- eventproduced by · An event is an occurrence, change, or associated record or notification recognized as significant within a system or context.
- domain layerpart of · A domain layer is an architectural part of an application that contains its domain concepts, rules, and behavior.
- domain-driven designpart of · Domain-driven design is a software design approach that centers models, structure, and terminology on the concepts, behavior, and boundaries of a problem domain.
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