Object-Relational Mappings: Generating JPA Entities

This document describes the following:

  1. Generating JPA Entities
  2. Related Information
    1. Connecting to a Database
    2. Creating JPA Projects

1. Generating JPA Entities

OEPE allows you to generate JPA entities using the entity generation tool called OEPE JPA Entity Generation Wizard.

Note that prior to using this tool, you should set up and configure the database connection, as well as add JPA support to your Eclipse project.

To generate JPA entities using the JPA Entity Generation Wizard, follow this procedure:

  1. Right-click your project in the Project Explorer and select JPA > Generate Custom JPA Entities from the drop-down menu, as Figure 1 shows. This will open the Generate Custom Entities dialog.



    Figure 1.     Generating Custom JPA Entities


  2. In the Generate Custom Entities > Select Tables dialog, specify the database connection and the schema. This will populate the Tables list, as Figure 2 shows.
  3. From the Tables list, select database tables for which you want to generate entities, as Figure 2 shows.



    Figure 2.     Generate Custom Entites Dialog


  4. Ensure that Synchronize Classes listed in persistence.xml is selected.
  5. Specify whether or not JDBC driver JARs should be added to the project classpath. Use this setting if your JPA project is running as a stand-alone Java application.
  6. Click Next.
  7. On the next screen, define properties of table associations. If you want to define new associations, click Create New Association. This will open the Create New Association dialog, as Figure 3 shows.



    Figure 3.     Create New Association Dialog


  8. On the Create New Association > Association Tables dialog, specify the association tables, as well as the type of association you want to create by selecting either Simple Association or Many to many Association, and then click Next.
  9. On the Create New Association > Join Columns screen, specify the join columns between the tables by clicking Add, as Figure 4 shows.



    Figure 4.     Create New Association Dialog - Join Columns


  10. On the Create New Association > Association Cardinality screen, specify the association cardinality of the relationship by selecting either Many to One, One to Many, or One to One, as Figure 5 shows, and then click Finish.



    Figure 5.     Create New Association Dialog - Association Cardinality


    The Generate Custom Entities dialog will display the table association that you have created. You can edit the association by clicking on it and modifying the field values on the bottom panel, as Figure 6 shows, and then click Next.



    Figure 6.     Table Association


  11. Skip entering values in the Generate Entities > Default Table Generation screen, as you are discouraged from using the default table generation, and click Next.
  12. In the Generate Custom Entities > Customize Individual Entities screen, specify generation properties for each indiviudual table and columns, as Figure 7 shows, and then click Finish.



    Figure 7.     Table Association


Upon the completion of the OEPE JPA Entity Generation Wizard, the generated JPA entity classes are automatically added to your project's persistence.xml file, as Figure 8 and Figure 9 show.



Figure 8. persistence.xml File





Figure 9. Generated Persistent Class




2. Related Information

Getting Started With the Oracle Database Plugin for Eclipse

Configuring a Persistence Provider for JPA Projects

2.1 Connecting to a Database

To set up a database connection using Eclipse IDE, follow this procedure:
  • Collect the information necessary to connect to your target database. This may include preparing the database schema.
    The following example shows a DDL script that you can use to create a database schema that Figure 4 demonstrates:
    DROP TABLE LINEITEM;
DROP TABLE ORDER_DATA;
DROP TABLE PRODUCT;
DROP TABLE CUSTOMERID;
DROP TABLE CUSTOMER;

CREATE TABLE CUSTOMER (
  CUSTOMERID INTEGER  NOT NULL,
  NAME CHAR(60) DEFAULT NULL NOT NULL
);
ALTER TABLE CUSTOMER ADD CONSTRAINT PK_CUSTOMERID PRIMARY KEY (CUSTOMERID);
 

CREATE TABLE CUSTOMERID (
  CUSTOMERID INTEGER  NOT NULL,
  DRV_LIC_NO INTEGER DEFAULT NULL NOT NULL
);
ALTER TABLE CUSTOMERID  ADD CONSTRAINT FK_CUSTOMERID FOREIGN KEY (CUSTOMERID) REFERENCES CUSTOMER (CUSTOMERID);
ALTER TABLE CUSTOMERID  ADD CONSTRAINT PK_CUSTOMER_DRV_LIC_ID PRIMARY KEY (CUSTOMERID, DRV_LIC_NO);

 
CREATE TABLE ORDER_DATA (
  ORDERID INTEGER  NOT NULL,
  AMOUNT DECIMAL(6 , 0) DEFAULT NULL NOT NULL,
  CUSTOMERID INTEGER DEFAULT NULL NOT NULL,
  ORDERDATE VARCHAR(64) DEFAULT NULL
);
ALTER TABLE ORDER_DATA ADD CONSTRAINT PK_ORDERID PRIMARY KEY (ORDERID);
ALTER TABLE ORDER_DATA ADD CONSTRAINT FK_ORDER_CUSTOMERID FOREIGN KEY (CUSTOMERID)
 REFERENCES CUSTOMER (CUSTOMERID);

 
CREATE TABLE PRODUCT (
  PRODUCTID INTEGER  NOT NULL,
  CODE VARCHAR(5) DEFAULT NULL,
  NAME VARCHAR(64) DEFAULT NULL,
  UNITPRICE DECIMAL(38 , 0) DEFAULT NULL NOT NULL
);
ALTER TABLE PRODUCT ADD CONSTRAINT PK_PRODUCTID PRIMARY KEY (PRODUCTID);


CREATE TABLE LINEITEM (
  ORDERLINE INTEGER  NOT NULL,
  ORDERID INTEGER DEFAULT NULL NOT NULL,
  PRODUCTID INTEGER DEFAULT NULL NOT NULL,
  QUANTITY DECIMAL(4 , 0) DEFAULT NULL NOT NULL
);
ALTER TABLE LINEITEM ADD CONSTRAINT PK_ORDERLINE PRIMARY KEY (ORDERLINE);
ALTER TABLE LINEITEM ADD CONSTRAINT FK_LINEITEM_PRODUCTID FOREIGN KEY (PRODUCTID)
 REFERENCES PRODUCT (PRODUCTID);
ALTER TABLE LINEITEM ADD CONSTRAINT FK_LINEITEM_ORDERID FOREIGN KEY (ORDERID)
 REFERENCES ORDER_DATA (ORDERID);



    Figure 10.     Sample Database Schema


  • Define a database connection using the Eclipse IDE's New Connection Profile Wizard, as follows:
    • Select the database connection type. This could be Oracle or Generic JDBC connection, for example.
    • Select JDBC driver.
    • Specify connection properties.
    • Test the database to ensure the connection properties are set correctly.
  • Connect to the database and examine the database schema using the Data Source Exploerer. For more information, see Connecting to an Oracle Database.



2.2 Creating JPA Projects

In order to use JPA, you need to be working within either a Web, EJB or utility project that supports JPA facet (includes the required libraries).

To create a new Eclipse JPA project, follow this procedure:

  1. Right-click the Project Explorer and select New > Project from the drop-down menu. This will open the New Project dialog.
  2. Select JPA > JPA Project from the list, as Figure 11 shows, and then click Next.



    Figure 11.     New Project Dialog


    3. This will open the New JPA Project dialog, as Figure 12 shows.



    Figure 12.     New JPA Project Dialog


  3. On the New JPA Project dialog, specify the following:
    • provide a name for your project;
    • select Oracle WebLogic Server v.N as your target runtime;
    • enter the appropriate value in Configuration field. To specify either EclipseLink or Oracle Kodo as your persistence provider, click Modify, and select either Java Persistence Library (EclipseLink), or a combination of Java Persistence Library (Oracle Kodo) and WebLogic Utility Module Extensions on the Project Facets dialog, as Figure 13 shows. For more information, see Configuring a Persistence Provider for JPA Projects.



      Figure 13.       Project Facets Dialog - JPA Configuration


    • optionally, select Add project to an EAR;
    • click Next.
  4. Optionally, make modifications on the New JPA Project > JPA Facet screen, making sure you specify the database connection in the Connection field, and then click Finish.


You can also add JPA support to an existing Eclipse project as follows:

  • Right-click your project in Project Explorer and select Properties from the drop-down menu. This will open the Properties dialog.
  • Select Project Facets from the tree control on the left, and then select Java Persistence, as well as one of Java Persitence Library (EclipseLink) or Java Persitence Library (Oracle Kodo) from the Project Facet list. For more information, see Configuring a Persistence Provider for JPA Projects
  • Click Further configuration available.... This will open the Modify Faceted Project dialog.
  • On the Modify Faceted Project dialog, make appropriate modifications, ensuring that you specify the database connection in the Connection field, and then click Next.
  • On the next screen, configure the JPA persistence provider libraries, and then click Finish.
  • Click Apply, and then OK on the Properties dialog.