Value Objects

Value objects are immutable domain elements that are distinguished by their properties rather than their identity. They are used to represent concepts in the domain that have no unique identity but are defined by their attributes.

Value objects help to create a rich domain model by encapsulating concepts that are often represented as simple types.

Facts

Value Objects are immutable.

Once created, the state of a value object cannot be changed. This immutability ensures that value objects preserve their integrity and consistency.

Value Objects are defined by their attributes.

The identity of a value object is based entirely on its attributes. Two value objects with the same attribute values are considered equal, regardless of their instance.

Value Objects are often used for descriptive purposes.

Value objects are ideal for representing descriptive aspects of the domain, such as measurements, monetary values, or other concepts that are defined by their values.

Value Objects enforce business rules.

Value objects can encapsulate business rules and constraints related to their attributes. They ensure that the values they hold are always valid and consistent.

Value Objects are nested within entities.

Value objects are enclosed within aggregates and entities to represent complex attributes.

Value Objects are persisted with entities.

Value objects are typically persisted as part of the entities or aggregates they belong to. Their persistence is managed implicitly through the enclosing entity or aggregate.

When an entity is persisted, any value objects it contains are also persisted. This ensures that the complete state of the entity, including its descriptive attributes, is stored.

Value Objects can be composed of Value Objects.

Value objects can be composed to form complex types, but they do not have independent identity and are always part of entities or aggregates.

Value Objects do not reference entities.

Value objects should not hold references to entities. They are self-contained and defined solely by their attributes.