Java Persistence with Hibernate

6.1. Sets, bags, lists, and maps of value types

An object of value type has no database identity; it belongs to an entity instance, and its persistent state is embedded in the table row of the owning entity—at least, if an entity has a reference to a single instance of a valuetype. If an entity class has a collection of value types (or a collection of references to value-typed instances), you need an additional table, the so-called collection table.

Before you map collections of value types to collection tables, remember that value-typed classes don't have identifiers or identifier properties. The lifespan of a value-type instance is bounded by the lifespan of the owning entity instance. A value type doesn't support shared references.

Java has ...