一个简单的复合主键的做关联类的例子(转自JavaEye)

robbin 论坛管理员 性别: 年龄:30 十二宫图: 加入时间: 2003/09/07 文章: 2028 来自: 上海	时间: 2004-10-20 16:12:30    标题: 一个简单的复合主键的做关联类的例子 我写这个例子的来由是因为haha1903提了一个这种类型的问题 http://forum.javaeye.com/viewtopic.php?t=8285 场景是这样的： 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： java代码:  /* * 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 );     } } java代码:  /* * 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;     } } java代码:  /* * 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 ( );     } } 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;     } }
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robbin 论坛管理员 性别: 年龄:30 十二宫图: 加入时间: 2003/09/07 文章: 2028 来自: 上海	时间: 2004-10-20 16:17:43    标题: 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>
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robbin 论坛管理员 性别: 年龄:30 十二宫图: 加入时间: 2003/09/07 文章: 2028 来自: 上海	时间: 2004-10-20 16:26:43    标题: 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。