Single-valued entity associations
We assume you won t have any difficulty creating the same mapping with annotations or changing the Java class to an entity, with an identifier property this is the only change you have to make. Now let s create the association mappings from other entities to that class. There are several choices, the first being a primary key one-to-one association. Figure 7.1 Address as an entity with two associations referencing the same instance 7.1.1 Shared primary key associations Rows in two tables related by a primary key association share the same primary key values. The main difficulty with this approach is ensuring that associated instances are assigned the same primary key value when the objects are saved. Before we try to solve this problem, let s see how you map the primary key association. Mapping a primary key association with XML The XML mapping element that maps an entity association to a shared primary key entity is . First you need a new property in the User class: public class User { … private Address shippingAddress; // Getters and setters } Next, map the association in User.hbm.xml: You add a cascading option that is natural for this model: If a User instance is made persistent, you usually also want its shippingAddress to become persistent. Hence, the following code is all that is needed to save both objects:
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