本篇介紹多對多的雙向關聯,多對多的處理方式是,有一張中間表,中間表保存兩個多方之間的關係。首先來看實際應用場景:一個用戶可能存在多種角色,一種角色也可能有多個用戶,所以用戶和角色之間是一個多對多的關係。實體:用戶(User),具有如下屬性:Id,名稱(name),角色列表(roles);實體:角色(Role),具有如下屬性:Id,名稱(name);
tb_user表的創建如圖所示:
tb_role表的創建如圖:
關聯表tb_usermappingrole:
三張表建立完成,下面介紹User類和Role類以及相關配置文件
Role類:
package com.hiberbate.manytomany;
import java.util.HashSet;
import java.util.Set;
public class Role {
private int id;
private String name;
private Set<User> users = new HashSet<User>();
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public Set<User> getUsers() {
return users;
}
public void setUsers(Set<User> uses) {
this.users = uses;
}
}
User類:
package com.hiberbate.manytomany;
import java.util.HashSet;
import java.util.Set;
public class User {
private int id;
private String name;
private Set<Role> roles = new HashSet<Role>();
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public Set<Role> getRoles() {
return roles;
}
public void setRoles(Set<Role> roles) {
this.roles = roles;
}
}
tb_user.hbm.xml配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hiberbate.manytomany">
<class name="User" table="tb_user">
<id name="id" column="id" type="int" >
<generator class="assigned" /> <!--generator這個坑,如果指定class爲native會導致外部程序設置的主鍵id無效,且根據數據庫自行判斷採用自增長式 -->
</id>
<property name="name" type="string">
<column name="name"/>
</property>
<set name="roles" table="tb_usermappingrole" cascade="all">
<!-- key標籤配置當前映射文件在第三張表外鍵名稱 -->
<key column="userid"></key>
<!--
class:角色實體類全路徑
column:角色在第三張表的外鍵名稱
-->
<many-to-many class="com.hiberbate.manytomany.Role" column="roleid"></many-to-many>
</set>
</class>
</hibernate-mapping>
tb_role.hbm.xml配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hiberbate.manytomany">
<class name="Role" table="tb_role">
<id name="id" column="id" type="int" >
<generator class="assigned" /> <!--generator這個坑,如果指定class爲native會導致外部程序設置的主鍵id無效,且根據數據庫自行判斷採用自增長式 -->
</id>
<property name="name" type="string">
<column name="name"/>
</property>
<set name="users" table="tb_usermappingrole" >
<!-- key標籤配置當前映射文件在第三張表外鍵名稱 -->
<key column="roleid"></key>
<!--
class:角色實體類全路徑
column:角色在第三張表的外鍵名稱
-->
<many-to-many class="com.hiberbate.manytomany.User" column="userid"></many-to-many>
</set>
</class>
</hibernate-mapping>
保存數據測試用例:
private static void manytomany() {
Session session = null;
User u1 = new User();
u1.setId(100);
u1.setName("admin");
User u2 = new User();
u2.setId(200);
u2.setName("張三");
Role r1 = new Role();
r1.setId(9);
r1.setName("超級管理員");
Role r2 = new Role();
r2.setId(8);
r2.setName("普通用戶");
Set<Role> roleSet1 = new HashSet<Role>();
roleSet1.add(r1);
roleSet1.add(r2);
u1.setRoles(roleSet1);
Set<Role> roleSet2 = new HashSet<Role>();
roleSet2.add(r2);
u2.setRoles(roleSet2);
try {
session = HibernateUtil.getSession();
//添加數據
session.beginTransaction();
session.save(u1);
session.save(u2);
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
System.out.print("數據庫添加失敗");
e.printStackTrace();
}finally{
HibernateUtil.closeSession();
}
}
測試結果如圖: