hibernate详解(三)----->>组件映射(二)之复合主键

 

   3、组件类作为持久化类的对象标识符属性

     这种情况主要是针对已经数据库表建模时，由于数据库表中采用联合自然主键(复合自然主键)，为了完成这种映射需求，Hibernate使用组件类把它映射成持久化类的对象标识符。

     Hibernate要求，作为复合对象标识符类的UserOid类必须实现Java.io.Serializable，且要用作为复合标识符的属性重写hashCode()方法和equlas()方法。

 

    User.java

 

package com.zxf.domain;


 /** 用户持久化类(实体类) */
 public class User {
     private UserOid id;                 //对象标识符(OID)
     private String description;      //描述

     public User(){}                 //无参数的构造方法

     //以下省略所有属性的getters和setters方法...

}

package com.zxf.domain;


/** 用户持久化类(实体类) */
public class User {
    private UserOid id;                 //对象标识符(OID)
    private String description;      //描述
   
    public User(){}                 //无参数的构造方法
   
    //以下省略所有属性的getters和setters方法...

}

 

   UserOid .java

 

 

package com.zxf.domain;


 /** 用户类的对象标识符类
 *  必须实现Serializable和重写hashCode()和equals()方法
 */
 public class UserOid implements java.io.Serializable {
     private static final long serialVersionUID = -9079299317576122433L;
     private String firstName;     //名
     private String lastName;      //姓

     public UserOid(){}            //无参数的构造方法

     //用fristName、lastName重写hashCode方法
     public int hashCode() {
         final int prime = 31;
         int result = 1;
         result = prime * result + ((firstName == null) ? 0 :

firstName.hashCode());
         result = prime * result + ((lastName == null) ? 0 :

lastName.hashCode());
         return result;
    }

     //用fristName、lastName重写equals方法
     public boolean equals(Object obj) {
         if (this == obj)    return true;
         if (obj == null)    return false;
         if (getClass() != obj.getClass())   return false;
        UserOid other = (UserOid) obj;
         if (firstName == null) {
             if (other.firstName != null)    return false;
         } else if (!firstName.equals(other.firstName))      return false;
         if (lastName == null) {
             if (other.lastName != null)     return false;
         } else if (!lastName.equals(other.lastName))    return false;
         return true;
    }

     //以下省略所有属性的getters和setters方法...
}

package com.zxf.domain;


/** 用户类的对象标识符类
 *  必须实现Serializable和重写hashCode()和equals()方法
 */
public class UserOid implements java.io.Serializable {
	private static final long serialVersionUID = -9079299317576122433L;
	private String firstName;     //名
	private String lastName;      //姓
	
	public UserOid(){}            //无参数的构造方法

	//用fristName、lastName重写hashCode方法
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result	+ ((firstName == null) ? 0 : 

firstName.hashCode());
		result = prime * result	+ ((lastName == null) ? 0 : 

lastName.hashCode());
		return result;
	}

	//用fristName、lastName重写equals方法
	public boolean equals(Object obj) {
		if (this == obj)	return true;
		if (obj == null)	return false;
		if (getClass() != obj.getClass())	return false;
		UserOid other = (UserOid) obj;
		if (firstName == null) {
			if (other.firstName != null)	return false;
		} else if (!firstName.equals(other.firstName))		return false;
		if (lastName == null) {
			if (other.lastName != null)		return false;
		} else if (!lastName.equals(other.lastName))	return false;
		return true;
	}

	//以下省略所有属性的getters和setters方法...
}

 

  User.hbm.xml

 

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
         "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
   <!-- 映射持久化类 -->
     <class name="com.zxf.domain.User" table="user">
        <!--
          composite-id元素映射复合对象标识符
          name属性：指定属性名
          class属性：指定对应的此属性的类类型
          -->
         <composite-id name="id" class="com.zxf.domain.UserOid">
             <!-- key-property元素映射组件类的的每个属性 -->
             <key-property name="firstName" column="first_name"/>
             <key-property name="lastName" column="last_name"/>
         </composite-id>
         <!-- 用property映射每个普通属性 -->
         <property name="description"/>
     </class>
 </hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
  <!-- 映射持久化类 -->
	<class name="com.zxf.domain.User" table="user">
		<!-- 
		  composite-id元素映射复合对象标识符
		  name属性：指定属性名
		  class属性：指定对应的此属性的类类型
		 -->
		<composite-id name="id" class="com.zxf.domain.UserOid">
			<!-- key-property元素映射组件类的的每个属性 -->
			<key-property name="firstName" column="first_name"/>
			<key-property name="lastName" column="last_name"/>
		</composite-id>
		<!-- 用property映射每个普通属性 -->
		<property name="description"/>		
	</class>
</hibernate-mapping>

 

   hibernate.cfg.xml

 

 

<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
     "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

 <hibernate-configuration>
     <session-factory>

         <!-- 数据库方言设置 -->
         <property name="hibernate.dialect">
            org.hibernate.dialect.MySQLInnoDBDialect
         </property>

         <!-- 数据库连接参数设置 -->
         <property name="hibernate.connection.driver_class">
            com.mysql.jdbc.Driver
         </property>
         <property

 name="hibernate.connection.url">jdbc:mysql:///hibernate</property>
         <property name="hibernate.connection.username">root</property>
         <property name="hibernate.connection.password">123</property>

         <!--实际操作数据库时是否显示SQL -->
         <!--
        <property name="hibernate.show_sql">true</property>-->
         <property name="hibernate.format_sql">true</property>


         <!--将数据库schema的DDL导出到数据库 -->
         <property name="hibernate.hbm2ddl.auto">update</property>

         <!-- 以下定义实体类与数据库表的映像文件 -->
         <mapping resource="com/zxf/domain/User.hbm.xml" />
     </session-factory>
 </hibernate-configuration>