Step 3. Create and Manage Entities

Time to complete this step: 30 minutes

The JPA ORM Generation wizard allows modification of existing O/R mappings and the creation of new entity associations.

The tasks you will complete in this step are:

• To Create a New One-to-One Association between CUSTOMER and CUSTOMERID
• To Review Generated Classes with Annotations
• To Add Annotations to an Existing Java Class
• To Run EJBQL to Verify that the New Mappings are Correct and Function Properly

To Create a New One-to-One Association between CUSTOMER and CUSTOMERID

Workshop also supports the creation of new entity associations in case your database lacks foreign key definitions (such as for performance reasons). It can create Simple Associations (one to one, one to many, many to one) between two tables and Many to Many Associations through an intermediate table.

1. In the DbXplorer view, right-click SalesDBConnection and select Generate JPA Mapping.
2. In the Web Application dialog, select workshop-jpa-tutorial and click OK.
3. In the JPA ORM Generation dialog, select all the database tables except CONTACT and click Next.

   

4. In the JPA ORM Generation dialog, click the Create New Association link.

   

5. In the Create New Association dialog, using the Table 1 drop down menu, select CUSTOMER.
   Using the Table 2 drop down menu, select CUSTOMERID.
   Click Next.
   
   This creates a simple one-to-one association between the CUSTOMER and CUSTOMERID tables.

   

6. Next we specify the join columns between the tables.
   
   Using the CUSTOMER table drop down menu, select the CUSTOMERID column.
   Using the CUSTOMERID table drop down menu, select the CUSTOMERID column.
   Click Next.



7. Select One-to-One to specify one customer per customerid.
   Click Finish.
   

   

Since the new associations (shown in brown) are not observed in the database schema, they will be annotated programmatically in the respective entity beans.

8. Click Next.
9. If necessary, on the Default Table Generation page, next to the Java Package field, click Browse. In the Choose Java Package dialog, select com.bea.beans and click OK.
10. On the Default Table Generation page, click Finish.

To Review Generated Classes with Annotations

Review the following annotations in the class Customer and CustomerId.

• One-to-One Properties - A one-to-one property designates a relationship in which an entity A references a single entity B, and no other As can reference the same B. This is a one-to-one relationship between A and B.

The following shows the one-to-one mapping association between Customer and CustomerId in the Customer class.

@OneToOne(fetch=FetchType.EAGER) @JoinColumn(name="CUSTOMERID", referencedColumnName="CUSTOMERID", nullable=false, insertable=false, updatable=false) public Customerid getCustomeridBean() { return this.customeridBean; } public void setCustomeridBean(Customerid customeridBean) { this.customeridBean = customeridBean; }

• The following shows the one-to-one mapping association between CustomerId and Customer in the CustomerId class.

@OneToOne(mappedBy="customeridBean", fetch=FetchType.EAGER) public Customer getCustomer() { return this.customer; } public void setCustomer(Customer customer) { this.customer = customer; }

Note: The annotation attributes for one-to-one mappings are similar to one-to-many and many-to-one annotation attributes as explained before in Step 2 of this tutorial: Review Generated Classes with Annotations.

To Add Annotations to an Existing Java Class

In this step, you will create a Java class Contact and use Workshop to annotate existing Java classes (POJOs) to make them into JPA entity beans. This way, we will follow a "top-down" development scenario.

1. Select File > New > Class.
2. In the Package field, enter com.bea.beans.
   In the Name field, enter Contact.
   In the Interfaces field, enter java.io.Serializable. (Click the Add button to fill in this field.)
   Select Constructors from superclass to add a no argument constructor.
   Click Finish.
   
   

   

3. Add the following set of private variables of type String to the Contact class. Note: We are defining properties that map to columns in the CONTACT database table.

   private String contactId; private String address; private String city; private String phone;

4. Add getter and setter methods for each property by right-clicking within the source view and selecting Source > Generate Getters and Setters. In the Generate Getters and Setters dialog, click Select All and click OK.
5. Add the following property.

   private static final long serialVersionUID = 1L;

6. Override the equals( ) and hashCode( ) methods as we are going to use Contact instances in Set.

   public boolean equals(Object other) {   if ( (this == other ) ) return true;   if ( !(other instanceof Contact) ) return false;   Contact castOther = (Contact) other;   if( this.getContactId( ).equals(castOther.getContactId( )) ) {     return true;   } else {     return false;   } } public int hashCode() {    return this.getContactId( ).hashCode( ); }

7. Save the Contact class. Now, we have the object representation for CONTACT persistence data. Next, we will annotate the Contact object.
8. In the AppXplorer view, right-click on the project workshop-jpa-tutorial. Choose New > Other. Expand JPA and select Annotate Java Class, then click Next.

   

9. Click Browse to select a Java Class. Type contact to view and select the com.bea.beans.Contact object to be mapped.
   Click OK.

   

10. In the Entity Access drop-down list, choose property and click Next. (Note by choosing property, you are instructing Workshop to annotate your class's accessors; if you choose field, Workshop annotates your class's fields.)

    

11. In the Class Mapping Properties dialog, confirm that the Database Table field has the value CONTACT and the Primary Key Property field has the value contactId.
    Click Next.

    

12. In the Bean Properties Mapping dialog, you can verify the mappings between fields and database columns that are being annotated in the Contact java class. Note that you can select a property mapping and click Edit to modify a selected property mapping. In this tutorial, we do not need to change any mapping information.
    
    Click Finish.
    
    

13. Edit the annotated class Contact to add a bi-directional many-to-one mapping association with Customer.
    • Import the following javax.persistence classes for adding a new many-to-one column join.

      import javax.persistence.JoinColumn; import javax.persistence.ManyToOne;

    • Add a property customer of type Customer.

      private Customer customer;

    • Add the following annotation to the Contact entity for adding a many-to-one association with Customer. The @JoinColumn annotation defines the attributes Column Name which is the name of the column to which the property is bound and the Referenced column which is the name of the primary key column being joined to.

      @ManyToOne() @JoinColumn(name="CUSTOMERID", referencedColumnName="CUSTOMERID") public Customer getCustomer() { return this.customer; } public void setCustomer(Customer customer) { this.customer = customer; }

    • Save the class Contact.
    
    
14. For the above many-to-one customer property in the Contact entity there should be a one-to-many contact property in the Customer entity.
• Open the class Customer.
• Add a property contacts of type java.util.Set

  private java.util.Set<Contact> contacts;

• Add the following annotation to the Customer entity for adding a one-to-many association with Contact. The @OnetoMany annotation defines the attribute MappedBy which is the name of the many-to-one field in the Contact entity that maps this bidirectional relation.

  @OneToMany(mappedBy="customer") public java.util.Set<Contact> getContacts() { return this.contacts; } public void setContacts(java.util.Set<Contact> contacts) { this.contacts = contacts; }

• Save the class Customer.

To Run EJBQL to Verify that the New Mappings are Correct and Function Properly

In this step we have created a new association between Customer and CustomerId Entities using the JPA ORM Mapping tool. Also we have annotated an existing Java class Contact to make it into a JPA entity bean. Use the EJBQL editor to test the runtime behaviors.

1. Test the bi-directional one-to-one mapping between Customer and CustomerId. Execute the following query in the EJBQL Editor:
   
   select c from Customer c where c.customeridBean.customerid = 101
   



1. Test the bi-directional one-to-one mapping between CustomerId and Customer. Execute the following query in the EJBQL Editor:
   
   select c from Customerid c where c.customer.customerid = 101
   
   



2. Test bi-directional many-to-one mapping between Contact and Customer. Execute the following query in the EJBQL Editor:
   
   select c from Contact c where c.customer.customerid = 101