Implementing Domain-Driven Design

Construction

When we newly instantiate an Entity, we want to use a constructor that captures enough state to fully identify it and enable clients to find it. When early identity generation is used, a correctly designed constructor takes as a parameter at least the unique identity. If the Entity is queried by other means, such as with a name or description, we would also include all such as constructor parameters.

Sometimes an Entity maintains one or more invariants. An invariant is a state that must stay transactionally consistent throughout the Entity life cycle. Invariants are a concern of Aggregates, but since the Aggregate Root is always an Entity, it is mentioned here. If an Entity has an invariant that is satisfied by the non-null state ...