Hibernate关联映射

集合映射 开发流程： 需求分析/数据库设计、项目设计/ 编码/测试/实施部署上线/验收需求: 用户购买， 填写地址！ // javabean设计 public class User { private int userId; private String userName; // 一个用户，对应的多个地址 private Set String addre

集合映射

<code>开发流程：
    需求分析/数据库设计、项目设计/ 编码/测试/实施部署上线/验收

需求:
    用户购买， 填写地址！
</code>

<code class=" hljs lasso"><span class="hljs-comment">// javabean设计</span>
<span class="hljs-keyword">public</span> class User {

    <span class="hljs-keyword">private</span> int userId;
    <span class="hljs-keyword">private</span> <span class="hljs-built_in">String</span> userName;
    <span class="hljs-comment">// 一个用户，对应的多个地址</span>
    <span class="hljs-keyword">private</span> <span class="hljs-built_in">Set</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> address;
    <span class="hljs-keyword">private</span> <span class="hljs-built_in">List</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> addressList <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> ArrayList<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>(); 
    <span class="hljs-comment">//private String[] addressArray; // 映射方式和list一样     <array name=""></array></span>
    <span class="hljs-keyword">private</span> <span class="hljs-built_in">Map</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span>,<span class="hljs-built_in">String</span><span class="hljs-subst">></span> addressMap <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> HashMap<span class="hljs-subst"><</span><span class="hljs-built_in">String</span>, <span class="hljs-built_in">String</span><span class="hljs-subst">></span>();

}
</code>

<code class=" hljs xml"><span class="hljs-comment"><!-- 映射文件 --></span>
<span class="hljs-pi"><?xml version="1.0"?></span>
<span class="hljs-doctype"><!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"></span>

<span class="hljs-tag"><<span class="hljs-title">hibernate-mapping</span> <span class="hljs-attribute">package</span>=<span class="hljs-value">"cn.itcast.a_collection"</span>></span>

    <span class="hljs-tag"><<span class="hljs-title">class</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"User"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_user"</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">id</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"userId"</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"id"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">generator</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"native"</span>></span><span class="hljs-tag"></<span class="hljs-title">generator</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">id</span>></span>   
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"userName"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>

        <span class="hljs-comment"><!-- 
            set集合属性的映射
                name 指定要映射的set集合的属性
                table 集合属性要映射到的表
                key  指定集合表(t_address)的外键字段
                element 指定集合表的其他字段
                    type 元素类型，一定要指定
         --></span>
         <span class="hljs-tag"><<span class="hljs-title">set</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"address"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_address"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"uid"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">element</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"address"</span> <span class="hljs-attribute">type</span>=<span class="hljs-value">"string"</span>></span><span class="hljs-tag"></<span class="hljs-title">element</span>></span>
         <span class="hljs-tag"></<span class="hljs-title">set</span>></span>

         <span class="hljs-comment"><!-- 
            list集合映射
                list-index  指定的是排序列的名称 (因为要保证list集合的有序)
          --></span>
          <span class="hljs-tag"><<span class="hljs-title">list</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"addressList"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_addressList"</span>></span>
              <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"uid"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
              <span class="hljs-tag"><<span class="hljs-title">list-index</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"idx"</span>></span><span class="hljs-tag"></<span class="hljs-title">list-index</span>></span>
              <span class="hljs-tag"><<span class="hljs-title">element</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"address"</span> <span class="hljs-attribute">type</span>=<span class="hljs-value">"string"</span>></span><span class="hljs-tag"></<span class="hljs-title">element</span>></span>
          <span class="hljs-tag"></<span class="hljs-title">list</span>></span>

          <span class="hljs-comment"><!-- 
            map集合的映射
                key  指定外键字段
                map-key 指定map的key 
                element  指定map的value
           --></span>
          <span class="hljs-tag"><<span class="hljs-title">map</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"addressMap"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_addressMap"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"uid"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">map-key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"shortName"</span> <span class="hljs-attribute">type</span>=<span class="hljs-value">"string"</span> ></span><span class="hljs-tag"></<span class="hljs-title">map-key</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">element</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"address"</span> <span class="hljs-attribute">type</span>=<span class="hljs-value">"string"</span> ></span><span class="hljs-tag"></<span class="hljs-title">element</span>></span>
          <span class="hljs-tag"></<span class="hljs-title">map</span>></span>         
    <span class="hljs-tag"></<span class="hljs-title">class</span>></span>
<span class="hljs-tag"></<span class="hljs-title">hibernate-mapping</span>></span></code>

<code class="language-java hljs ">    <span class="hljs-comment">// 测试程序</span>
    <span class="hljs-comment">// 保存set</span>
    <span class="hljs-annotation">@Test</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">testSaveSet</span>() <span class="hljs-keyword">throws</span> Exception {
        Session session = sf.openSession();
        session.beginTransaction();

        <span class="hljs-comment">//-- 保存</span>
        Set<String> addressSet = <span class="hljs-keyword">new</span> HashSet<String>();
        addressSet.add(<span class="hljs-string">"广州"</span>);
        addressSet.add(<span class="hljs-string">"深圳"</span>);
        <span class="hljs-comment">// 用户对象</span>
        User user = <span class="hljs-keyword">new</span> User();
        user.setUserName(<span class="hljs-string">"Jack"</span>);
        user.setAddress(addressSet);

        <span class="hljs-comment">// 保存</span>
        session.save(user);

        session.getTransaction().commit();
        session.close();
    }

    <span class="hljs-comment">// 保存list/map</span>
    <span class="hljs-annotation">@Test</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">testSaveList</span>() <span class="hljs-keyword">throws</span> Exception {
        Session session = sf.openSession();
        session.beginTransaction();
        User user = <span class="hljs-keyword">new</span> User();
        user.setUserName(<span class="hljs-string">"Tom"</span>);
<span class="hljs-comment">//      // 用户对象  --  list</span>
<span class="hljs-comment">//      user.getAddressList().add("广州");</span>
<span class="hljs-comment">//      user.getAddressList().add("深圳");</span>
<span class="hljs-comment">//      // 保存</span>
<span class="hljs-comment">//      session.save(user);</span>

        <span class="hljs-comment">// 用户对象  --  Map</span>
        user.getAddressMap().put(<span class="hljs-string">"A0001"</span>, <span class="hljs-string">"广州"</span>);
        user.getAddressMap().put(<span class="hljs-string">"A0002"</span>, <span class="hljs-string">"深圳"</span>);

        <span class="hljs-comment">// 保存</span>
        session.save(user);

        session.getTransaction().commit();
        session.close();
    }
</code>

<code>问题：
    集合映射，映射的集合元素，都是普通的类型， 能否为对象类型？
</code>

关联映射

<code>需求1：
    部门与员工
          一个部门有多个员工;       【一对多】
          多个员工，属于一个部门    【多对一】
需求2：
    项目与开发员工
        一个项目，有多个开发人员！
        一个开发人员，参与多个项目！   【多对多】
</code>

多对一映射与一对多

<code>1. 需求：员工与部门
2. 数据库：
3. 设计javabean封装：
4. 映射：
</code>

JavaBean

<code class=" hljs cs"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> Dept {

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> deptId;
    <span class="hljs-keyword">private</span> String deptName;
    <span class="hljs-comment">// 【一对多】 部门对应的多个员工</span>
    <span class="hljs-keyword">private</span> Set<Employee> emps = <span class="hljs-keyword">new</span> HashSet<Employee>();
}   
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> Employee {

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> empId;
    <span class="hljs-keyword">private</span> String empName;
    <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> salary;
    <span class="hljs-comment">// 【多对一】员工与部门</span>
    <span class="hljs-keyword">private</span> Dept dept;
}</code>

Dept.hbm.xml

<code class=" hljs xml"><span class="hljs-pi"><?xml version="1.0"?></span>
<span class="hljs-doctype"><!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"></span>

<span class="hljs-tag"><<span class="hljs-title">hibernate-mapping</span> <span class="hljs-attribute">package</span>=<span class="hljs-value">"cn.itcast.b_one2Many"</span>></span>

    <span class="hljs-tag"><<span class="hljs-title">class</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"Dept"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_dept"</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">id</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"deptId"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">generator</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"native"</span>></span><span class="hljs-tag"></<span class="hljs-title">generator</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">id</span>></span>   
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"deptName"</span> <span class="hljs-attribute">length</span>=<span class="hljs-value">"20"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>

        <span class="hljs-comment"><!-- 
            一对多关联映射配置  （通过部门管理到员工）
            Dept 映射关键点：
            1.  指定 映射的集合属性： "emps"
            2.  集合属性对应的集合表： "t_employee"
            3.  集合表的外键字段   "t_employee. dept_id"
            4.  集合元素的类型

         --></span>
         <span class="hljs-tag"><<span class="hljs-title">set</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"emps"</span>></span>   <span class="hljs-comment"><!-- table="t_employee" --></span>
             <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"dept_id"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
             <span class="hljs-tag"><<span class="hljs-title">one-to-many</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"Employee"</span>/></span>
         <span class="hljs-tag"></<span class="hljs-title">set</span>></span>      
    <span class="hljs-tag"></<span class="hljs-title">class</span>></span>
<span class="hljs-tag"></<span class="hljs-title">hibernate-mapping</span>></span></code>

Employee.hbm.xml

<code class=" hljs xml"><span class="hljs-pi"><?xml version="1.0"?></span>
<span class="hljs-doctype"><!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"></span>

<span class="hljs-tag"><<span class="hljs-title">hibernate-mapping</span> <span class="hljs-attribute">package</span>=<span class="hljs-value">"cn.itcast.b_one2Many"</span>></span>

    <span class="hljs-tag"><<span class="hljs-title">class</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"Employee"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_employee"</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">id</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"empId"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">generator</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"native"</span>></span><span class="hljs-tag"></<span class="hljs-title">generator</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">id</span>></span>   
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"empName"</span> <span class="hljs-attribute">length</span>=<span class="hljs-value">"20"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"salary"</span> <span class="hljs-attribute">type</span>=<span class="hljs-value">"double"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>

        <span class="hljs-comment"><!-- 
            多对一映射配置
            Employee 映射关键点：
            1.  映射的部门属性  ：  dept
            2.  映射的部门属性，对应的外键字段: dept_id
            3.  部门的类型
         --></span>
         <span class="hljs-tag"><<span class="hljs-title">many-to-one</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"dept"</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"dept_id"</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"Dept"</span>></span><span class="hljs-tag"></<span class="hljs-title">many-to-one</span>></span>       
    <span class="hljs-tag"></<span class="hljs-title">class</span>></span>
<span class="hljs-tag"></<span class="hljs-title">hibernate-mapping</span>></span></code>

测试

<code class=" hljs java">
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">App</span> {</span>

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> SessionFactory sf;
    <span class="hljs-keyword">static</span> {
        sf = <span class="hljs-keyword">new</span> Configuration()
            .configure()
            .addClass(Dept.class)   
            .addClass(Employee.class)   <span class="hljs-comment">// 测试时候使用</span>
            .buildSessionFactory();
    }

    <span class="hljs-comment">// 保存， 部门方 【一的一方法操作】</span>
    <span class="hljs-annotation">@Test</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">save</span>() {

        Session session = sf.openSession();
        session.beginTransaction();

        <span class="hljs-comment">// 部门对象</span>
        Dept dept = <span class="hljs-keyword">new</span> Dept();
        dept.setDeptName(<span class="hljs-string">"应用开发部"</span>);
        <span class="hljs-comment">// 员工对象</span>
        Employee emp_zs = <span class="hljs-keyword">new</span> Employee();
        emp_zs.setEmpName(<span class="hljs-string">"张三"</span>);
        Employee emp_ls = <span class="hljs-keyword">new</span> Employee();
        emp_ls.setEmpName(<span class="hljs-string">"李四"</span>);
        <span class="hljs-comment">// 关系</span>
        dept.getEmps().add(emp_zs);
        dept.getEmps().add(emp_ls);

        <span class="hljs-comment">// 保存</span>
        session.save(emp_zs);
        session.save(emp_ls);
        session.save(dept); <span class="hljs-comment">// 保存部门，部门下所有的员工  </span>

        session.getTransaction().commit();
        session.close();
        <span class="hljs-comment">/*
         *  结果
         *  Hibernate: insert into t_employee (empName, salary, dept_id) values (?, ?, ?)
            Hibernate: insert into t_employee (empName, salary, dept_id) values (?, ?, ?)
            Hibernate: insert into t_dept (deptName) values (?)
            Hibernate: update t_employee set deptId=? where empId=?    维护员工引用的部门的id
            Hibernate: update t_employee set deptId=? where empId=?
         */</span>
    }
    <span class="hljs-comment">// 【推荐】 保存， 部员方 【多的一方法操作】</span>
    <span class="hljs-annotation">@Test</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">save2</span>() {

        Session session = sf.openSession();
        session.beginTransaction();

        <span class="hljs-comment">// 部门对象</span>
        Dept dept = <span class="hljs-keyword">new</span> Dept();
        dept.setDeptName(<span class="hljs-string">"综合部"</span>);
        <span class="hljs-comment">// 员工对象</span>
        Employee emp_zs = <span class="hljs-keyword">new</span> Employee();
        emp_zs.setEmpName(<span class="hljs-string">"张三"</span>);
        Employee emp_ls = <span class="hljs-keyword">new</span> Employee();
        emp_ls.setEmpName(<span class="hljs-string">"李四"</span>);
        <span class="hljs-comment">// 关系</span>
        emp_zs.setDept(dept);
        emp_ls.setDept(dept);


        <span class="hljs-comment">// 保存</span>
        session.save(dept); <span class="hljs-comment">// 先保存一的方法</span>
        session.save(emp_zs);
        session.save(emp_ls);<span class="hljs-comment">// 再保存多的一方，关系回自动维护(映射配置完)</span>

        session.getTransaction().commit();
        session.close();
        <span class="hljs-comment">/*
         *  结果
         *  Hibernate: insert into t_dept (deptName) values (?)
            Hibernate: insert into t_employee (empName, salary, dept_id) values (?, ?, ?)
            Hibernate: insert into t_employee (empName, salary, dept_id) values (?, ?, ?)
            少生成2条update  sql
         */</span>
    }
}</code>

总结

<code>  在一对多与多对一的关联关系中，保存数据最好的通过多的一方来维护关系，这样可以减少update语句的生成，从而提高hibernate的执行效率！

配置一对多与多对一，这种叫“双向关联”
只配置一对多，           叫“单项一对多”
只配置多对一，           叫“单项多对一”

注意：
    配置了哪一方，哪一方才有维护关联关系的权限！
</code>

Inverse属性

<code>Inverse属性，是在维护关联关系的时候起作用的。
       表示控制权是否转移。(在一的一方起作用)

Inverse , 控制反转。
Inverse = false  不反转；   当前方有控制权
        True  控制反转； 当前方没有控制权

维护关联关系中，是否设置inverse属性：

    1. 保存数据 
        有影响。
       如果设置控制反转,即inverse=true, 然后通过部门方维护关联关系。在保存部门的时候，同时保存员工， 数据会保存，但关联关系不会维护。即外键字段为NULL
</code>

<code>    2. 获取数据
        无。
    3. 解除关联关系？
        有影响。
        inverse=false，  可以解除关联
        inverse=true，  当前方(部门)没有控制权，不能解除关联关系
        (不会生成update语句,也不会报错)
    4. 删除数据对关联关系的影响？
        有影响。
        inverse=false, 有控制权， 可以删除。先清空外键引用，再删除数据。
        inverse=true,  没有控制权: 如果删除的记录有被外键引用，会报错，违反主外键引用约束！  如果删除的记录没有被引用，可以直接删除。
</code>

cascade 属性

<code>cascade  表示级联操作  【可以设置到一的一方或多的一方】
    none                  不级联操作， 默认值
    save-update           级联保存或更新
    delete                级联删除
    save-update,delete    级联保存、更新、删除
    all                   同上。级联保存、更新、删除
</code>

多对多映射

<code>需求：项目与开发人员
      Project   Developer
      电商系统
           曹吉
           王春
       OA系统
            王春
            老张
</code>

JavaBean

<code class=" hljs cs"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> Developer {
    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> d_id;
    <span class="hljs-keyword">private</span> String d_name;
    <span class="hljs-comment">// 开发人员，参数的多个项目</span>
    <span class="hljs-keyword">private</span> Set<Project> projects = <span class="hljs-keyword">new</span> HashSet<Project>();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> Project {
    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> prj_id;
    <span class="hljs-keyword">private</span> String prj_name;
    <span class="hljs-comment">// 项目下的多个员工</span>
    <span class="hljs-keyword">private</span> Set<Developer> developers = <span class="hljs-keyword">new</span> HashSet<Developer>();
}</code>

Project.hbm.xml

<code class=" hljs xml"><span class="hljs-pi"><?xml version="1.0"?></span>
<span class="hljs-doctype"><!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"></span>

<span class="hljs-tag"><<span class="hljs-title">hibernate-mapping</span> <span class="hljs-attribute">package</span>=<span class="hljs-value">"cn.itcast.c_many2many"</span>></span>

    <span class="hljs-tag"><<span class="hljs-title">class</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"Project"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_project"</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">id</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"prj_id"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">generator</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"native"</span>></span><span class="hljs-tag"></<span class="hljs-title">generator</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">id</span>></span>   
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"prj_name"</span> <span class="hljs-attribute">length</span>=<span class="hljs-value">"20"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>
        <span class="hljs-comment"><!-- 
            多对多映射:
            1.  映射的集合属性： “developers”
            2.  集合属性，对应的中间表： “t_relation”
            3. 外键字段:  prjId
            4. 外键字段，对应的中间表字段:  did
            5.   集合属性元素的类型
         --></span>
         <span class="hljs-tag"><<span class="hljs-title">set</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"developers"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_relation"</span> <span class="hljs-attribute">cascade</span>=<span class="hljs-value">"save-update"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"prjId"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">many-to-many</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"did"</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"Developer"</span>></span><span class="hljs-tag"></<span class="hljs-title">many-to-many</span>></span>
         <span class="hljs-tag"></<span class="hljs-title">set</span>></span>      
    <span class="hljs-tag"></<span class="hljs-title">class</span>></span>
<span class="hljs-tag"></<span class="hljs-title">hibernate-mapping</span>></span></code>

Developer.hbm.xml

<code class=" hljs xml"><span class="hljs-pi"><?xml version="1.0"?></span>
<span class="hljs-doctype"><!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"></span>

<span class="hljs-tag"><<span class="hljs-title">hibernate-mapping</span> <span class="hljs-attribute">package</span>=<span class="hljs-value">"cn.itcast.c_many2many"</span>></span>

    <span class="hljs-tag"><<span class="hljs-title">class</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"Developer"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_developer"</span>></span>
        <span class="hljs-tag"><<span class="hljs-title">id</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"d_id"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">generator</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"native"</span>></span><span class="hljs-tag"></<span class="hljs-title">generator</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">id</span>></span>   
        <span class="hljs-tag"><<span class="hljs-title">property</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"d_name"</span> <span class="hljs-attribute">length</span>=<span class="hljs-value">"20"</span>></span><span class="hljs-tag"></<span class="hljs-title">property</span>></span>

        <span class="hljs-comment"><!-- 
            多对多映射配置： 员工方
                name  指定映射的集合属性
                table 集合属性对应的中间表
                key   指定中间表的外键字段(引用当前表t_developer主键的外键字段)
                many-to-many
                    column 指定外键字段对应的项目字段
                    class  集合元素的类型
         --></span>
        <span class="hljs-tag"><<span class="hljs-title">set</span> <span class="hljs-attribute">name</span>=<span class="hljs-value">"projects"</span> <span class="hljs-attribute">table</span>=<span class="hljs-value">"t_relation"</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">key</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"did"</span>></span><span class="hljs-tag"></<span class="hljs-title">key</span>></span>
            <span class="hljs-tag"><<span class="hljs-title">many-to-many</span> <span class="hljs-attribute">column</span>=<span class="hljs-value">"prjId"</span> <span class="hljs-attribute">class</span>=<span class="hljs-value">"Project"</span>></span><span class="hljs-tag"></<span class="hljs-title">many-to-many</span>></span>
        <span class="hljs-tag"></<span class="hljs-title">set</span>></span>       
    <span class="hljs-tag"></<span class="hljs-title">class</span>></span>
<span class="hljs-tag"></<span class="hljs-title">hibernate-mapping</span>></span></code>

维护关联关系

<code>设置inverse属性，在多对多种维护关联关系的影响？

1） 保存数据
    有影响。
    inverse=false ，有控制权，可以维护关联关系； 保存数据的时候会把对象关系插入中间表；
    inverse=true,  没有控制权， 不会往中间表插入数据。

2） 获取数据
    无。

3） 解除关系
    有影响。
    inverse=false ,有控制权， 解除关系就是删除中间表的数据。
    inverse=true, 没有控制权，不能解除关系。

4） 删除数据
    有影响。
    inverse=false, 有控制权。 先删除中间表数据，再删除自身。
    inverse=true, 没有控制权。 如果删除的数据有被引用，会报错！ 否则，才可以删除
</code>