집 >데이터 베이스 >MySQL 튜토리얼 >Hibernate关联映射
Hibernate关联映射
- WBOY원래의
- 2016-06-07 14:49:391273검색
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>
성명：
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