Defining a Basic Entity Bean

The following figure shows the design view of a basic entity bean called ProductBean:

This bean was developed by defining it from scratch, adding the two CMP fields, labeling one of these as the primary key, and creating an ejbCreate method (for more details, see How Do I: Add a Create Method to an Entity Bean?). These steps were accomplished in design view. This entity bean allows you to add a new product, find a product using its primary key, and getting and setting its CMP field values. The source code of this bean is given below:

package myBeans;

import javax.ejb.*;
import weblogic.ejb.*;

/**
 * @ejbgen:entity prim-key-class="java.lang.String"
 *   ejb-name = "Product"
 *   data-source-name="cgSampleDataSource"
 *   table-name = "product"
 *   abstract-schema-name = "Product"
 *
 * @ejbgen:jndi-name
 *   local  = "ejb.ProductLocalHome"
 *
 * @ejbgen:file-generation local-class = "True" local-class-name = "Product" local-home = "True" 
 *    local-home-name = "ProductHome" remote-class = "False" remote-home = "False" 
 remote-home-name = "ProductRemoteHome" 
 *    remote-class-name = "ProductRemote" value-class = "False" value-class-name = "ProductValue" 
 pk-class = "True"
 *
 */
abstract public class ProductBean extends GenericEntityBean implements EntityBean
{

    /**
     * @ejbgen:cmp-field primkey-field="true" column="Name"
     * @ejbgen:local-method
     */
    public abstract String getName();

    /**
     * @ejbgen:local-method
     */
    public abstract void setName(String arg);

    /**
     * @ejbgen:cmp-field column="Price"
     * @ejbgen:local-method
     */
    public abstract double getPrice();

    /**
     * @ejbgen:local-method
     */
    public abstract void setPrice(double arg);

    public java.lang.String ejbCreate(java.lang.String Name, double Price)
    {
      setName(Name);
      setPrice(Price);

      return null; // FIXME return PK value 
    }

    public void ejbPostCreate(java.lang.String Name, double Price)
    {
    }
}

In WebLogic, all the information needed to make an entity bean is stored in a single file, instead of separate JAVA files for the bean class, the local business interface, the local home interface, its primary key class, and so forth. When you build an EJB, these other classes are auto-generated. Various ejbgen annotations are used to hold the information required to make this generation possible. For example, the @ejbgen:file-generation annotation specifies the names of the local home and business interface for the ProductBean. The @ejbgen:local-method annotations on the accessor methods specify that these methods are defined in the local business interface. To verify that these JAVA and corresponding CLASS files are generated, expand the JAR file created during a build (located in the Modules folder in the Application pane), and locate and open the generated files in the folder reflecting the package name. For the ProductBean, the ProductBean.java (bean definition), Product.java (local interface definition), and ProductHome.java (local home interface definition) files are auto-generated.

If the ProductBean were to use multiple primary keys, the ProductBeanPK.java file containing the definition of the compound primary key class would also be auto-generated. For instance, the following figure shows a redefined ProductBean with an additional primary key manufacturer:

Notice in the above figure that the compound primary key is the return value of the ejbCreate method. Also, the auto-generated method findByPrimaryKey(myBeans.ProductBeanPK primaryKey) uses the compound primary key to obtain a bean instance reference.

Finally a value object class can also be auto-generated. For more information, see the Value Object Sample

• The local interface extends javax.ejb.EJBLocalObject
• The local home interface extends javax.ejb.EJBLocalHome
• The remote interface extends javax.ejb.EJBObject
• The remote home interface extends javax.ejb.EJBHome

Complete details about these interfaces and the methods they define can be found in your favorite J2EE documentation and the API reference at http://java.sun.com. One of the more frequently used methods provided by these 'extended' interfaces is a remove method, used to remove an entity bean instance. In other words, when you invoke the remove method on an entity bean, you remove the bean and the underlying record in the database. Remove methods are defined in all the interfaces. For instance, to remove a bean instance via the local home interface, you can invoke a remove method that takes instance's primary key as the parameter. To remove a bean instance via the local interface, you can invoked the remove method for the instance you want to remove. Both approaches are shown below; the session bean's method deleteViaHome deletes an instance of the Product bean via its local home interface, while deleteViaBusiness delete a Product bean instance via the local interface:

/**
 * ...
 *
 * @ejbgen:ejb-local-ref link="Product"
 */
public class SomeSession extends GenericSessionBean implements SessionBean
{
   ...

    /**
     * @ejbgen:local-method
     */
    public void deleteViaHome(myBeans.ProductBeanPK thePk)
    {
       try {        
          javax.naming.Context ic = new InitialContext();
          ProductHome productHome = (ProductHome)ic.lookup("java:comp/env/ejb/Product");
          productHome.remove(thePk);
       }
       catch(NamingException ne) {
          ...
       }
       catch(RemoveException re) {
          ...
       }
    }

   /**
     * @ejbgen:local-method
     */
    public void deleteViaBusiness(myBeans.ProductBeanPK thePk)
    {
       try {        
          javax.naming.Context ic = new InitialContext();
          ProductHome productHome = (ProductHome)ic.lookup("java:comp/env/ejb/Product");
          Product theProduct = productHome.findByPrimaryKey(thePk);
          theProduct.remove();
       }
       catch(NamingException ne) {
          ...
       }
       catch(FinderException ne) {
          ...
       }       
       catch(RemoveException re) {
          ...
       }
    }

   ...
}

create sequence myOracleSequence
start with 1 
nomaxvalue; 

@ejbgen:automatic-key-generation type="Oracle" name="myOracleSequence" cache-size="3" 

CREATE TABLE Customer (Customer_ID int IDENTITY(1,1), FirstName varchar(30) LastName varchar(30))

@ejbgen:automatic-key-generation type="SQLServer"

CREATE Table MyNamedSequence (SEQUENCE number);

INSERT into MyNamedSequence VALUES (0);

@ejbgen:automatic-key-generation name="MySequence" type="MyNamedSequenceTable" cache-size="100" 

 /**
 * @ejbgen:automatic-key-generation name="MyNamedSequence" type="NamedSequenceTable"
 cache-size="100"
 * 
 * @ejbgen:entity prim-key-class="java.lang.Integer"
 *   ejb-name = "Customer"
 *   data-source-name = "MyCustomerDataSource"
 *   table-name = "customer"
 *   abstract-schema-name = "Customer"
 *
 * ...
 */
abstract public class Customer extends GenericEntityBean implements EntityBean
{
    ...

    /**
     * @ejbgen:cmp-field primkey-field="true" column="Customer_ID"
     * @ejbgen:local-method
     */
    public abstract Integer getCustomer_ID();

    /**
     * @ejbgen:local-method
     */
    public abstract void setCustomer_ID(Integer arg);

    public java.lang.Integer ejbCreate(java.lang.String LastName, java.lang.String FirstName)
    {
      setLastName(LastName);
      setFirstName(FirstName);

      return null; // FIXME return PK value 
    }
}

   public void setAddress(String street, String apt, String city, String state, String zip) throws CreateException
   {
       Address currentAddress = this.getAddress( );
       if (currentAddress == null) {
           // Customer's current address not known.	
           newAddress = addressHome.create(street, apt, city, state, zip);
           setAddress(newAddress);
       } 
       else {
           // Update customer's current address. 
           currentAddress.setStreet(street);
           currentAddress.setApt(apt);
           currentAddress.setCity(city);
           currentAddress.setState(state);
           currentAddress.setZip(zip);
       }
   }

   public void addRecording(String recording) throws CreateException
   {
      Recording album = recordingHome.create(getBandName(), recording);
      Collection recordings = getRecordings();
      if(album != null) {
         recordings.add(album);
      }
    }

abstract public class ConcertBean extends GenericEntityBean implements EntityBean
{
   ...

   public Integer ejbCreate(String bandName, Venue theVenue) {
       setBandName(bandName);
       return null;
   }
	
   public void ejbPostCreate(String bandName, Venue theVenue) {
       setVenue(theVenue);
   }

   ...