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Figure 8.10 Modeling inheritance using joined tables. Each entity in the OO hierarchy corresponds to a separate table and parent-child relationships are modeled using one-to-one mapping.

In the preceding example, I had you drag the Behavior right onto the object in the Objects and Timeline panel, but you should know that you can also drag Behaviors right onto objects in the artboard as well.

@Entity @Table(name="USERS") @Inheritance(strategy=InheritanceType.JOINED) @DiscriminatorColumn(name="USER_TYPE", discriminatorType=STRING, length=1) public abstract class User ... @Entity @Table(name="SELLERS") @DiscriminatorValue(value="S") @PrimaryKeyJoinColumn(name="USER_ID") public class Seller extends User ... @Entity @Table(name="BIDDERS") @DiscriminatorValue(value="B") @PrimaryKeyJoinColumn(name="USER_ID") public class Seller extends User ...

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Listing 8.13 uses the @DiscriminatorColumn and @DiscriminatorValue annotations in exactly the same way as the single-table strategy. The @Inheritance annotation s strategy element is specified as JOINED, however. In addition, the one-toone relationships between parent and child tables are implemented through the @PrimaryKeyJoinColumn annotations in both the Seller and Bidder entities. In both cases, the name element specifies the USER_ID foreign key. The joined-tables strategy is probably the best mapping choice from a design perspective. From a performance perspective, it is worse than the single-table strategy because it requires the joining of multiple tables for polymorphic queries.

Figure 7-10. The MouseDragElementBehavior Behavior is now under the [Ellipse] in the Objects and Timeline panel. Press F5 to run the application again and notice that you have an Ellipse on the page now. Use your mouse to click and drag the Ellipse. Notice how it drags just that quickly we were able to make this object one that can be dragged about the page. If you ever made an object drag prior to the addition of Behaviors, you know it was a time-consuming, difficult task. The MouseDragElementBehavior Behavior allows us to accomplish this in less than a minute! Now let s look at one more Behavior called the ControlStoryboardAction Behavior. To do this we need to create a simple Storyboard. Let s make a Storyboard now.

Table-per-class is probably the simplest inheritance strategy for a layperson to understand. However, this inheritance strategy is the worst from both a relational and OO standpoint. In this strategy, both the superclass (concrete class) and subclasses are stored in their own table and no relationship exists between any of the tables. To see how this works, take a look at the tables in figure 8.11. As figure 8.11 shows, entity data are stored in their own tables even if they are inherited from the superclass. This is true even for the USER_ID primary key. As a

Figure 8.11 The table-per-class inheritance strategy. Super- and subclasses are stored in their own, entirely unrelated tables.

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The Animation workspace has more vertical space to allow for easier viewing of your Objects and Timeline panel to create and view Storyboards.

result, primary keys in all tables must be mutually exclusive for this scheme to work. In addition, inherited columns are duplicated across tables, such as the USERNAME column. Using this inheritance strategy, we define the strategy in the superclass and map tables for all the classes. Listing 8.14 shows how the code might look.

2. Click the New Storyboard icon, as shown in Figure 7-11.

package ejb3inaction.example.buslogic; ... import javax.persistence.PersistenceContext; import javax.persistence.EntityManager; ... @Stateless