Hibernate - Value Types

Greetings!

When we design our domain models we can have more important classes and less important classes like Address, String, etc. In other word we have fine-grained object model which means more classes than tables.
For an example User can have an Address. We can create separate class for Address fields and add it as a property in User using composition.

public class User {
    private Long id;
    private String name;
    private Integer age;
    private Address address;
}

Here User is an entity. Name, Age, Address are value types.

• Entity classes need an identifier.
• Value type doesn't have an identifier because instances are identified through owning entity.

What is an Entity?

• Has a database identity.
• Has it's own life cycle.
• Object reference is persisted in the database.

What is a Value Type?

• Doesn't have own identity.
• Embedded into owning entity.
• Represent table columns.

How to map?

• Basic types can be directly mapped using @Column. (String, Integer, etc)
• Collection value types using collection mapping.
• Composite value types can be mapped using @Embedable annotation.