在前文hibernate之5.many2one单向提到多对多关系，表结构设计是基于中间表来实现,
以下以用户与角色（多对多）为例,在Hibernate是怎样操作的
表结构设计:
类图:
CRUD;
Student
package com.demo.model; import java.io.UnsupportedEncodingException;
import java.util.Set; /**学生信息
* @author wobendiankun
*2014-10-19 下午08:54:29
*/
public class Student {
private int studentId ;
private String studentName ;
private int age;
private Set<Certificate> certificates ;
private User user;
public int getStudentId() {
return studentId;
}
public void setStudentId(int studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
String str="";
if(studentName!=null){
try {
str=new String(studentName.getBytes("UTF-8"));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
return "Student [studentId=" + studentId + ", studentName="
+ str + ", age=" + age + "]";
}
public Set<Certificate> getCertificates() {
return certificates;
}
public void setCertificates(Set<Certificate> certificates) {
this.certificates = certificates;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
} }Role
package com.demo.model; import java.util.Set; /**角色信息
* @author wobendiankun
*2014-11-2 下午08:29:54
*/
public class Role {
/**
* 角色id
*/
private int roleId;
/**
* 角色名称
*/
private String roleName; public Role() {
} public Role(int roleId) {
this.roleId = roleId;
} public Role(String roleName) {
this.roleName = roleName;
} private Set<User> users;
public int getRoleId() {
return roleId;
}
public void setRoleId(int roleId) {
this.roleId = roleId;
}
public String getRoleName() {
return roleName;
}
public void setRoleName(String roleName) {
this.roleName = roleName;
}
public Set<User> getUsers() {
return users;
}
public void setUsers(Set<User> users) {
this.users = users;
} }配置:
Role.hbm.xml
<? xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping > <class name="com.demo.model.Role" table="t_role">
<id name="roleId" column="role_id">
<generator class="sequence">
<param name="sequence">SEQ_T_ROLE</param>
</generator>
</id>
<property name="roleName" column="role_name" />
<set name="users" table="t_user_role" lazy="extra">
<key column="role_id"></key>
<many-to-many class="com.demo.model.User" column="user_id"></many-to-many>
</set>
</class>
</hibernate-mapping>
<set name="users" table="t_user_role" lazy="extra">
<key column="role_id"></key>
<many-to-many class="com.demo.model.User" column="user_id"></many-to-many>
</set>set元素的table属性::指中间表名
key元素的column属性:指表t_role在中间表中的关联字段
many-to-many元素的class属性:指set中的元素类型 ,column:User实体映射表t_user在中间表的关联字段
add:
</pre><pre name="code" class="java">@Test
<span style="white-space:pre"> </span>public void addTest() {
<span style="white-space:pre"> </span>User user1=new User("李三","111");
<span style="white-space:pre"> </span>User user2=new User("李四","111");
<span style="white-space:pre"> </span>Set<User> users=new HashSet<User>();
<span style="white-space:pre"> </span>users.add(user1);
<span style="white-space:pre"> </span>users.add(user2);
<span style="white-space:pre"> </span>
<span style="white-space:pre"> </span>Role role=new Role("开发组");
<span style="white-space:pre"> </span>role.setUsers(users);
<span style="white-space:pre"> </span>Session session = null;
<span style="white-space:pre"> </span>try {
<span style="white-space:pre"> </span>session = HibernateUtil.openSession();
<span style="white-space:pre"> </span>session.beginTransaction();
<span style="white-space:pre"> </span>session.save(user1);
<span style="white-space:pre"> </span>session.save(user2);
<span style="white-space:pre"> </span>session.save(role);
<span style="white-space:pre"> </span>session.getTransaction().commit();
<span style="white-space:pre"> </span>} catch (Exception e) {
<span style="white-space:pre"> </span>session.getTransaction().rollback();
<span style="white-space:pre"> </span>e.printStackTrace();
<span style="white-space:pre"> </span>} finally {
<span style="white-space:pre"> </span>HibernateUtil.closeSession(session);
<span style="white-space:pre"> </span>}
<span style="white-space:pre"> </span>}发出sql:
Hibernate: insert into t_user (user_name, password, student_id, user_id) values (?, ? , ?, ?)
Hibernate: insert into t_user (user_name, password, student_id, user_id) values (?, ?, ? , ? )
Hibernate: insert into t_role (role_name, role_id) values (?, ?)
Hibernate: insert into t_user_role (role_id, user_id) values (?, ? )
Hibernate: insert into t_user_role (role_id, user_id) values (?, ?)load
@Test
public void loadTest(){
Session session = null;
try {
session = HibernateUtil.openSession();
session.beginTransaction();
Role role=(Role)session.load(Role.class,2);
System.out.println("角色名称"+role.getRoleName());
System.out.println("users:"+role.getUsers());
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
} finally {
HibernateUtil.closeSession(session);
}
}发出sql:
Hibernate: select role0_.role_id as role1_3_0_, role0_.role_name as role2_3_0_ from t_role role0_ where role0_.role_id=?
角色名称开发组
Hibernate: select users0_.role_id as role1_3_1_, users0_.user_id as user2_1_, user1_.user_id as user1_2_0_, user1_.user_name as user2_2_0_, user1_.password as password2_0_, user1_.student_id as student4_2_0_ from t_user_role users0_ inner join t_user user1_ on users0_.user_id=user1_.user_id where users0_.role_id=?
users:[com.demo.model.User@b4be3d, com.demo.model.User@35bb0f]