Hibernate复合主键

HIbernate有两种方法来处理复合主键，第一种是基于实体类属性的复合主键，另一种是基于主键类的复合主键。在这里使用基于主键类的复合主键。
通常将复合主键相关属性，单独抽取出来，建立一个独立的类，这个类就是主键类，要求：
  * 必须实现序列化(Serializable)接口
  * 必须重写equals和hashcode方法
 
  复合主键的值是一个主键类，而不是一个普通的常见数值，因此，复合主键在映射文件中采用<composite-id>标签进行标识，其它属性采用<property>正常映射。

 

 建立一个主键类Timestamp,代码如下:

public class Timestamp implements Serializable{

   private String date;
   private String time;

   public String getDate() {
      return date;
   }

   public void setDate(String date) {
      this.date = date;
   }

   public String getTime() {
      return time;
   }

   public void setTime(String time) {
      this.time = time
   }

   //重写equals方法
   public boolean equals(Object other) {
      if(this == other) {
         return true;
      }
      if(other == null) {
         return false;
      }
      if(!(other instanceof Timestamp)) {
         return false;
      }
      
      Timestamp castOther = (Timestamp)other;

      //根据业务需要,设定比较条件
    return ((this.getDate() == castOther.getDate()) 
                  ||  (this.getDate() != null && castOther.getDate() != null
                  && this.getDate().equals(castOther.getDate())))
                   
                  && ((this.getTime() == castOther.getTime())
                  || (this.getTime() != null && castOther.getTime() !=null
                  && this.getTime().equals(castOther.getTime())));
  }

   //重写hashCode()方法
   public int hashCode() {
      int result = 17;

      result = 37 * result + 
                     (getDate() == null ? 0 : this.getDate().hashCode());
       
      result = 37 * result + 
                     (getTime() == null ? 0 : this.getTime().hashCode());

      return result;
   }
}

 

建立以主键类Timestamp为其中一个属性的bean类,代码如下:

public class Message implements Serializable {
   private Timestamp timestamp;
   private String messageId;
   private String messageContent;

   public Timestamp getTimestamp() {
      return timestamp;
   }

   public void setTimestamp(Timestamp timestamp) {
      this.timestamp = timestamp;
   }

   public String getMessageId() {
      return messageId;
   }

   public void setMessageId(String messageId) {
      this.messageId = messageId;
   }

   public String getMessageContent() {
       return messageContent;
   }

   public void setMessageContent(String messageContent) {
       this.messageContent = messageContent;
   } 
}

 

建立映射文件Message.hbm.xml,并在hibernate.cfg.xml文件中加入该映射文件,Message.hbm.xml文件内容如下:

<?xml version="1.0"?>   
<!DOCTYPE hibernate-mapping PUBLIC    
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">   
<hibernate-mapping>   
    <class name="com.iprai.hibernate.Message" table="message">   
        <composite-id name="timestamp">   
            <key-property name="date" column="idate"/>   
            <key-property name="time" column="itime"/>   
        </composite-id>   
        <property name="messageId" column="message_id"/>   
        <property name="messageContent" column="message_content"/>  
    </class>   
</hibernate-mapping> 

 

编写JUnit测试代码如下：

import java.util.Date;   
  
import org.hibernate.Session;   
  
import junit.framework.TestCase;   
  
public class MessageTest extends TestCase {   
       
    public void testSave() {   
        Session session = null;   
        try {   
            session = HibernateUtils.getSession();   
            session.beginTransaction();   
               
            //复合主键   
        Timestamp timestamp = new Timestamp();   
            timestamp.setDate("2009-12-05");   
            timestamp.setTime("17:01:23");   
               
            Message message = new Message();
            //和主键建立关联
        message.setTimestamp(message);   
            message.setMessageId("01");   
            message.setMessageContent("JavaEye");
               
            session.save(message);
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();   
        }finally {
            HibernateUtils.closeSession(session);   
        }   
    }   
       
    public void testLoad() {   
        Session session = null;   
        try {   
            session = HibernateUtils.getSession();  
        //复合主键   
        Timestamp timestamp = new Timestamp();   
            timestamp.setDate("2009-12-05");   
            timestamp.setTime("17:01:23");   

            Message message = (Message)session.load(Message.class, timestamp);   
            System.out.println("MessageId=" + message.getMessageId());   
            System.out.println("MessageContent=" + message.getMessageContent());   
        }catch(Exception e) {
            e.printStackTrace();
        }finally {
            HibernateUtils.closeSession(session);   
        }   
    }
}