一个简单的复合主键的做关联类的例子

用户类User，物品类Goods，每次记录用户使用物品的情况，情况包括谁在什么时间借了什么物品。其中有一个约束条件就是用户只能对同一物品使用一次。使用记录类为Record类。我们可以看出User对Record是1:n多的关系，Record对Goods是n:1的关系，而User和Goods之间没有之间的关系。

RecordId类是复合主键类，分别以n:1关联User类，n:1关联Goods类。RecordId类需要实现equals方法，需要实现Serializable。而Record类用RecordId来做主键。

类定义如下：

User.java

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

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

/**
 * @author robbin
 *
 */
public class User {

    private Long id;

    private String name;

    private Set usingRecords = new HashSet();

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

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

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

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

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

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

    public void 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);
    }

    public void removeRecord(Record record) {
        usingRecords.remove(record);
    }
}

 User .java

/*

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

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

/**
 * @author robbin
 *  
 */
public class User {

    private Long id;

    private String name;

    private Set usingRecords = new HashSet();

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

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

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

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

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

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

    public void 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);
    }

    public void removeRecord(Record record) {
        usingRecords.remove(record);
    }
}

Good.java

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

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

/**
 * @author robbin
 *
 */
public class Goods {

    private Long id;

    private String name;

    private Set usedRecords = new HashSet();

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

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

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

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

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

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

}

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

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

/**
 * @author robbin
 *  
 */
public class Goods {

    private Long id;

    private String name;

    private Set usedRecords = new HashSet();

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

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

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

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

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

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

}

RecordId .java

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

import java.io.Serializable;

/**
 * @author robbin
 *
 */
public class RecordId implements Serializable {

    private User user;

    private Goods goods;

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

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

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

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

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

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

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

import java.io.Serializable;

/**
 * @author robbin
 *  
 */
public class RecordId implements Serializable {

    private User user;

    private Goods goods;

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

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

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

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

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

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

Record .java

Java代码

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

import java.util.Calendar;

/**
 * @author robbin
 *
 */
public class Record {

    private RecordId recordId;

    private Calendar recordTime;

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

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

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

    /**
     * @param recordTime
     *            The recordTime to set.
     */
    public void setRecordTime(Calendar recordTime) {
        this.recordTime = recordTime;
    }
}

射文件配置如下：

<?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 version="1.0"?&gt;
<!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 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 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 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：  
     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); 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：  
     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("...");
} 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。