13: Factories

Chapter Roadmap

• Learn why the use of Factories can produce expressive models that adhere to Ubiquitous Language

• See how factory methods can be used as Aggregate Behaviors

• Consider how to use Factory Methods to create Aggregate instances of their types

• Learn how Domain Services can be designed as Factories while interacting with other Bounded Contexts and translating foreign objects to local types.

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Factories in the Domain Model

• Shift the responsibility of creating instances of complex objects and Aggregates to a separate object.

• Even if these objects have no responsibility in the domain model, they are still part of the domain model.

• Factories provide an interface that encapsulates complex assembly without requiring the client to reference concrete classes of objects instantiated.

• Factories can create an entire Aggregates as a piece while enforcing their invariants.

• An aggregate root that provides a Factory for another Aggregate type will have the primary responsibility of providing main aggregate behavior, the Factory being just one of those.

• Factory Methods on aggregates allow you to express the Ubiquitous Language in way not possible through constructors.

• When the behavioral name is expressive with respect to the Ubiquitous Language, we have a powerful case for using a Factory Method.