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Figure 8.2 An entity can be mapped to more than one table; for example, the User entity spans more than one table: USERS and USER_PICTURES. The primary table is mapped using @Table and the secondary table is mapped using @SecondaryTable. The primary and secondary tables must have the same primary key.

3. Click the Add state icon, as I am doing in Figure 16-26.

@Target({TYPE}) @Retention(RUNTIME) public @interface SecondaryTable { String name(); String catalog() default ""; String schema() default ""; PrimaryKeyJoinColumn[] pkJoinColumns() default {}; UniqueConstraint[] uniqueConstraints() default {}; }

Notice that other than the pkJoinColumns element, the definition of the annotation is identical to the definition of the @Table annotation. This element is the key to how annotation works. To see what we mean, examine the following code implementing the User entity mapped to two tables:

panel and check the IsHitTestVisible property in the Common Properties bucket. This will allow the DialogBox to be clicked once again.

The Zenophile module (http://drupal.org/project/zenophile) automates the process of creating Zen subthemes, removing all manual tasks required when creating subthemes. It includes two submodules:

@Entity @Table(name="USERS") @SecondaryTable(name="USER_PICTURES", pkJoinColumns=@PrimaryKeyJoinColumn(name="USER_ID")) public class User implements Serializable { ..}

Obviously, the two tables in @Table and @SecondaryTable are related somehow and are joined to create the entity. This kind of relationship is implemented by creating a foreign key in the secondary table referencing the primary key in the first table. In this case, the foreign key also happens to be the primary key of the secondary table. To be precise, USER_ID is the primary key of the USER_PICTURES table and it references the primary key of the USERS table. The pkJoinColumns=@PrimaryKeyJoinColumn(name="USER_ID") specification assumes this relationship. The name element points to the USER_ID foreign key in the USER_PICTURES secondary table. The persistence provider is left to figure out what the primary key of the USERS table is, which also happens to be named USER_ID. The provider performs a join using the detected primary key in order to fetch the data for the User entity. In the extremely unlikely case that an entity consists of columns from more than two tables, we may use the @SecondaryTables annotation more than once for the same entity. We won t cover this case here, but encourage you to explore it if needed. Before we conclude the section on mapping entities, let s discuss a vital feature of JPA: primary key generation.

in Figure 16-27.

You may want to work around this by having your servlets implement SingleThreadModel. Although doing so may seem harmless, keep in mind that this is a deprecated feature (since servlet 2.4) and we don t recommend using it because of the many limitations it imposes on applications. This topic is beyond the scope of this book (see www.esus.com/ javaindex/j2ee/servlets/servletdiffthread.html).

Zenophile Midnight, which adds CSS and graphics for creating a light-on-dark subtheme Zenophile Sidebars, which allows you to adjust the width and placement of sidebars without manually changing code

The right way to use a container-managed EntityManager is by avoiding dependency injection and instead performing a JNDI lookup. Bear in mind that the JNDI lookup mechanism can be used in any nonmanaged or managed class. To use a container-managed EntityManager, you must first establish the references to the persistence unit using either the @PersistenceContext annotation at the class level or the persistence-context-ref element in web.xml. If you re using a managed class such as a servlet or JSF managed bean, then you can establish the reference as follows:

Now we have the Visual States we need to actually hook them up to do something. Specifically, we want the Buy Now buttons to activate the ShowDialog state so that the DialogBox will appear and be able to be clicked.

@PersistenceContext(name = "actionBazaar/EntityManager", unitName = "actionBazaar") public class ActionBazaarBidControllerServlet extends HttpServlet { private EntityManager entityManager; ... }

ShowDialog, as I am doing in Figure 16-28.

If you are using a web framework like Struts where the action classes are not managed, then you can t use annotations to establish references to the persistence context. In this case you will have to use the persistence-context-ref element in the web.xml as follows: