hibernate学习之七(hibernate映射map详解)

原来我们无论是学习一对多还是多对多,只有有集合的地方我们都是用的set来完成的,如果我们需要用map集合的时候,项目中该怎么实现那;

简单了解篇

下面我先来写一个简单的.从数据库看是2个表,但是从实体类看就一个实体类,和一个映射文件:

实体类

public class Customers implements java.io.Serializable {

    private Long id;
    private String name;
    private Map orders;

映射文件

<hibernate-mapping>
    <class name="com.wfg.map1.Customers" table="customers" >
        <id name="id" type="java.lang.Long">
            <column name="ID" />
            <generator class="native" />
        id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="15" />
        property>
        <map name="orders"  table="orders">
             <key column="CUSTOMER_ID">key>
             
            <index column="orderNumber" type="java.lang.String">index>   
            
            <element column="oderdesc" type="java.lang.String">element>
        map>
    class>
hibernate-mapping>

测试代码

Customers customers = new Customers();
            customers.setId(new Long(1));
            customers.setName("customers1");
            customers.setOrders(new HashMap());

            customers.getOrders().put("zhangsan", "hello ");
            customers.getOrders().put("lisi", "word");
            customers.getOrders().put("wangwu", "welcom");


            session.save(customers);

map升级了解

从上面的例子中我们可以看到orders表中再有其他的信息就不能实现了.我们下面来实现
实体类

public class Team {

    private int id;
    private String name;
    private Map students;

public class Student {

    private int id;
    private String name;
    private String card_id;
    private String studendesc;
    private Team team;

映射文件
Student映射文件不再介绍和原来说的一对多 多的一方一样有many-to-one标签
team映射文件

<hibernate-mapping>
    <class name="com.wfg.map2.Team" table="team" >
        <id name="id" type="integer">
            <column name="ID" />
            <generator class="native" />
        id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="15" />
        property>
       <map name="students" table="student" cascade="all">
             <key column="team_id">key>
            <index column="card_id" type="string">index> 
            <one-to-many class="com.wfg.map2.Student"/>
       map>
    class>
hibernate-mapping>

测试代码

Team team = new Team();
            team.setName("team1");
            team.setStudents(new HashMap());

            Student stu = new Student();
            stu.setName("张三");
            stu.setStudendesc("hello");

            Student stu2 = new Student();
            stu2.setName("李四");
            stu2.setStudendesc("word");

            team.getStudents().put("100", stu);
            team.getStudents().put("101", stu2);
            session.save(team);

不解释下面在map标签中加inverse=”true”
此时是:

但是我去数据库发现

这次解释下为什么,维护inverse=true 也就是说这种关联关系让Student维护,但是Student并不知道card_id,和team_id的值
我将测试代码修改了下

Team team = new Team();
            team.setName("team1");
            team.setStudents(new HashMap());

            Student stu = new Student();
            stu.setName("张三");
            stu.setStudendesc("hello");
            stu.setTeam(team);
            stu.setCard_id("200");

            Student stu2 = new Student();
            stu2.setName("李四");
            stu2.setCard_id("201");
            stu2.setStudendesc("word");
            stu2.setTeam(team);

            team.getStudents().put("100", stu);
            team.getStudents().put("101", stu2);
            session.save(team);

源码下载
链接：http://pan.baidu.com/s/1minxw7m 密码：1oil