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

OEPE 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 Project Explorer, right-click the project oepe-jpa-tutorial and select JPA > Generate Entities from Tables... ick Next.

  2. Select the database tables from the Select Tables dialog as shown below. Select all the database tables except CONTACT and click Next.

  3. In the Table Associations dialog, click the Create New Association button.

  4. In the Create New Association dialog, select the CUSTOMER table for Table 1 and the CUSTOMERID table for Table 2 (as shown below) and click Next. This creates a simple one-to-one association between the CUSTOMER and CUSTOMERID tables.

  5. In the Join Columns dialog, specify the join columns between tables. Select the CUSTOMERID column for the CUSTOMER table and the CUSTOMERID column for the CUSTOMERID table.

    6. Click Next.

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

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


  7. Click Finish.
     

To Review Generated Classes with Annotations

Review the following annotations in the class Customer and CustomerId.

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;
}

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 within 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. Under the package com.bea.beans, create a Java class Contact which implements the java.io.Serializable interface. Select Constructors from superclass to add a no argument constructor.

  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 with source view and selecting Source > Generate Getters and Setters. In the Generate Getters and Setters dialog, select all properties 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 Project Explorer view, right-click on the project oepe-jpa-tutorial. Choose JPA > Generate Entity from 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. When choosing Property, OEPE will annotate your class's accessor methods; if you choose field, OEPE annotate your class's fields. Set the Entity Access to Property and click Next.

  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. If not, select it.
    Then 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.
  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.

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