eclipse + JBoss 5 + EJB3开发指南（11）：实体Bean的连接策略（JOINED Strategy）

     package  entity;

import  javax.persistence.Column;
import  javax.persistence.DiscriminatorColumn;
import  javax.persistence.Entity;
import  javax.persistence.GeneratedValue;
import  javax.persistence.GenerationType;
import  javax.persistence.Id;
import  javax.persistence.Inheritance;
import  javax.persistence.InheritanceType;
import  javax.persistence.Table;

@Entity
@Table(name = " t_myaccounts " )
@Inheritance(strategy = InheritanceType.JOINED)
public   class  Account
{
     protected  String id; 
     protected   float  balance;
     protected  String type;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = " account_id " )
     public  String getId()
    {
         return  id;
    }
     public   void  setId(String id)
    {
         this .id  =  id;
    }
     public   float  getBalance()
    {
         return  balance;
    }
     public   void  setBalance( float  balance)
    {
         this .balance  =  balance;
    }
    @Column(name = " account_type " )
     public  String getType()
    {
         return  type;
    }
     public   void  setType(String type)
    {
         this .type  =  type;
    }
}

  从上面的代码可以看出，只使用了@Inheritance 对实体Bean 进行注释。
     下面编写MyCheckingAccount 和MySavingsAccount 类的代码：

MyCheckingAccount 类的代码：

package  entity;

import  javax.persistence.Column;
import  javax.persistence.DiscriminatorValue;
import  javax.persistence.Entity;
import  javax.persistence.Id;
import  javax.persistence.PrimaryKeyJoinColumn;
import  javax.persistence.Table;

@Entity
@Table(name = " t_checkingaccount " )
//   指定与Account类共享的主键名
@PrimaryKeyJoinColumn(name = " account_id " ) 
public   class  MyCheckingAccount  extends  Account
{
     private   double  overdraftLimit;
     public  MyCheckingAccount()
    {
       //   为account_type字段赋默认值
        setType( " C " );
    }
    @Column(name = " overdraft_limit " )
     public   double  getOverdraftLimit()
    {
         return  overdraftLimit;
    }

     public   void  setOverdraftLimit( double  overdraftLimit)
    {
         this .overdraftLimit  =  overdraftLimit;
    }
}

MySavingsAccount类的代码：

package  entity;

import  javax.persistence.Column;
import  javax.persistence.DiscriminatorValue;
import  javax.persistence.Entity;
import  javax.persistence.Id;
import  javax.persistence.PrimaryKeyJoinColumn;
import  javax.persistence.Table;

@Entity
@Table(name = " t_savingsaccount " )
@PrimaryKeyJoinColumn(name = " account_id " ) 
public   class  MySavingsAccount  extends  Account
{
    
     private   double  interestRate;
     public  MySavingsAccount()
    {
       //   为account_type字段赋默认值
        setType( " S " );
    }
  @Column(name = " interest_rate " )
     public   double  getInterestRate()
    {
         return  interestRate;
    }
     public   void  setInterestRate( double  interestRate)
    {
         this .interestRate  =  interestRate;
    }    
}

    在上面的代码中使用构造方法来初始化了t_myaccounts 表的account_type 字段的值。  
    可以使用下面的代码进行测试：

System.out.println(((MyCheckingAccount)em.createQuery( " from MyCheckingAccount where id=12 " )
    .getSingleResult()).getBalance());
MyCheckingAccount ca  =   new  MyCheckingAccount();
ca.setBalance( 342 );
ca.setOverdraftLimit( 120 );
em.persist(ca);
MySavingsAccount sa  =   new  MySavingsAccount();
sa.setBalance( 200 );
sa.setInterestRate( 321 );

em.persist(sa);

 本文转自 androidguy 51CTO博客，原文链接： http://blog.51cto.com/androidguy/214425 ，如需转载请自行联系原作者