Implementing Domain-Driven Design

Reject Undue Influence of Data Model Leakage

Probably most times that a Value Object is persisted to a data store (for example, using an ORM tool along with a relational database) it is stored in a denormalized fashion; that is, its attributes are stored in the same database table row as its parent Entity object. This makes the storage and retrieval of Values clean and optimized and prevents any persistence store leakage into the model. It’s both a pleasure and a relief when Values can be persisted this way.

There are times, however, when a Value Object in the model will of necessity be stored as an Entity with respect to a relational persistence store. In other words, when persisted, an instance of a specific Value Object type will occupy its ...