Koska's BLOG

/*
* Created on 2004-10-20
*
*/
package com.javaeye;

import java.util.Calendar;
import java.util.HashSet;
import java.util.Set;

/**
* @author robbin
* 
*/
publicclass User {

    privateLong id;

    privateString name;

    privateSet usingRecords = newHashSet();

    /**
     * @return Returns the id.
     */
    publicLong getId(){
        return id;
    }

    /**
     * @param id
     *            The id to set.
     */
    publicvoid setId(Long id){
        this.id = id;
    }

    /**
     * @return Returns the name.
     */
    publicString getName(){
        return name;
    }

    /**
     * @param name
     *            The name to set.
     */
    publicvoid setName(String name){
        this.name = name;
    }

    /**
     * @return Returns the usingRecords.
     */
    publicSet getUsingRecords(){
        return usingRecords;
    }

    /**
     * @param usingRecords
     *            The usingRecords to set.
     */
    publicvoid setUsingRecords(Set usingRecords){
        this.usingRecords = usingRecords;
    }

    publicvoid useGoods(Goods goods){
        RecordId id = new RecordId();
        id.setUser(this);
        id.setGoods(goods);
        Record record = new Record();
        record.setRecordId(id);
        record.setRecordTime(Calendar.getInstance());
        usingRecords.add(record);
    }

    publicvoid removeRecord(Record record){
        usingRecords.remove(record);
    }
}

/*
* Created on 2004-10-20
*
*/
package com.javaeye;

import java.util.HashSet;
import java.util.Set;

/**
* @author robbin
* 
*/
publicclass Goods {

    privateLong id;

    privateString name;

    privateSet usedRecords = newHashSet();

    /**
     * @return Returns the id.
     */
    publicLong getId(){
        return id;
    }

    /**
     * @param id
     *            The id to set.
     */
    publicvoid setId(Long id){
        this.id = id;
    }

    /**
     * @return Returns the name.
     */
    publicString getName(){
        return name;
    }

    /**
     * @param name
     *            The name to set.
     */
    publicvoid setName(String name){
        this.name = name;
    }

    /**
     * @return Returns the usedRecords.
     */
    publicSet getUsedRecords(){
        return usedRecords;
    }

    /**
     * @param usedRecords
     *            The usedRecords to set.
     */
    publicvoid setUsedRecords(Set usedRecords){
        this.usedRecords = usedRecords;
    }

}

/*
* Created on 2004-10-20
*
*/
package com.javaeye;

import java.io.Serializable;

/**
* @author robbin
* 
*/
publicclass RecordId implementsSerializable{

    private User user;

    private Goods goods;

    /**
     * @return Returns the goods.
     */
    public Goods getGoods(){
        return goods;
    }

    /**
     * @param goods
     *            The goods to set.
     */
    publicvoid setGoods(Goods goods){
        this.goods = goods;
    }

    /**
     * @return Returns the user.
     */
    public User getUser(){
        return user;
    }

    /**
     * @param user
     *            The user to set.
     */
    publicvoid setUser(User user){
        this.user = user;
    }

    publicboolean equals(Object obj){
        return(obj instanceof RecordId)
                && (this.getUser().equals(((RecordId) obj).getUser()))
                && (this.getGoods().equals(((RecordId) obj).getGoods()));
    }

    publicint hashCode(){
        return this.getUser().hashCode() ^ this.getGoods().hashCode();
    }
}

/*
* Created on 2004-10-20
*
*/
package com.javaeye;

import java.util.Calendar;

/**
* @author robbin
* 
*/
publicclass Record {

    private RecordId recordId;

    privateCalendar recordTime;

    /**
     * @return Returns the recordId.
     */
    public RecordId getRecordId(){
        return recordId;
    }

    /**
     * @param recordId
     *            The recordId to set.
     */
    publicvoid setRecordId(RecordId recordId){
        this.recordId = recordId;
    }

    /**
     * @return Returns the recordTime.
     */
    publicCalendar getRecordTime(){
        return recordTime;
    }

    /**
     * @param recordTime
     *            The recordTime to set.
     */
    publicvoid setRecordTime(Calendar recordTime){
        this.recordTime = recordTime;
    }
}
映射文件配置如下：

xml代码:

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC         "-//Hibernate/Hibernate Mapping DTD 2.0//EN"         "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"> <hibernate-mapping>         <class name="com.javaeye.User">                 <id name="id" unsaved-value="null">                         <generator class="native"/>                 </id>                                 <property name="name"/>                                 <set name="usingRecords" inverse="true" lazy="true" cascade="all-delete-orphan">                         <key column="user_id" />                         <one-to-many class="com.javaeye.Record"/>                 </set>         </class>         </hibernate-mapping>

xml代码:

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC         "-//Hibernate/Hibernate Mapping DTD 2.0//EN"         "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"> <hibernate-mapping>         <class name="com.javaeye.Goods">                 <id name="id" unsaved-value="null">                         <generator class="native"/>                 </id>                                 <property name="name"/>                                 <set name="usedRecords" inverse="false" lazy="true" cascade="all-delete-orphan">                         <key column="goods_id" />                         <one-to-many class="com.javaeye.Record"/>                 </set>         </class>         </hibernate-mapping>

xml代码:

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC         "-//Hibernate/Hibernate Mapping DTD 2.0//EN"         "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"> <hibernate-mapping>         <class name="com.javaeye.Record">                 <composite-id name="recordId" class="com.javaeye.RecordId" unsaved-value="any" >                         <key-many-to-one name="user" column="user_id" class="com.javaeye.User" />                         <key-many-to-one name="goods" column="goods_id" class="com.javaeye.Goods" />                 </composite-id>                                 <property name="recordTime" type="calendar"/>         </class>         </hibernate-mapping>

记录物品使用情况的代码书写如下：

java代码:

Goods goods = new Goods(); goods.setName("book"); s.save(goods); User user = new User(); user.setName("robbin"); s.save(user); // 用户使用物品 user.useGoods(goods);

当用户重复使用物品的时候，调用userGoods方法，Hibernate会抛出主键重复的错误。

判断用户是否使用某物品的办法如下：

java代码:

RecordId id = new RecordId(); id.setUser(user); id.setGoods(goods); Record record = (Record) session.get(Record.class, id); if(record == null){     user.usGoods(goods); }else{     throw new UsedGoodsException("..."); }

然而需要指出的是，Gavin King并不提倡使用composite-id，如果你不是基于已有的数据库编程，而是重新设计数据库结构，那么建议使用UserType。你可以自定义 一个UserType，包括User和Goods，并且在hbm中定义该UserType为unique的，同样可以达到目的。而这种方式的好处则是不需 要你来手工维护id，而由Hibernate自动维护。UserType的使用方法参考手册5.2.4节和Hibernate自带的示例中的 net.sf.hibernate.test.DoubleStringType。