Hibernate关联关系映射—多对多详解编程语言

多对多
实例：学生–课程
实例分析：

代码实现：

Student.java

package com.my.bean; 

import java.util.HashSet; 

import java.util.Set; 

public class Student { 

 private Integer id; //native 

 private String name; 

 //不同的学生可以学习不同课程 (多对多) 

 // 当前学生可以学习【多个课程】 

 private Set Course courseSet = new HashSet Course 

 public Integer getId() { 

 return id; 

 public void setId(Integer id) { 

 this.id = id; 

 public String getName() { 

 return name; 

 public void setName(String name) { 

 this.name = name; 

 public Set Course getCourseSet() { 

 return courseSet; 

 public void setCourseSet(Set Course courseSet) { 

 this.courseSet = courseSet; 

Student.hbm.xml

 ?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 

 class name="com.my.bean.Student" table="t_student" 

 id name="id" 

 generator /generator 

 /id 

 property name="name" /property 

 !-- 

 不同的学生可以学习不同课程 (多对多),当前学生可以学习 

 1 使用集合 ## 从表表名 

 2 从表对应的外键名称 

 3 关联关系(多对多):类型，另一个外键名称 

 set name="courseSet" table="t_student_course" !-- cascade="save-update,delete" -- 

 key column="student_id" /key 

 many-to-many column="course_id" /many-to-many 

 /set 

 /class 

 /hibernate-mapping 

Course.java

package com.my.bean; 

import java.util.HashSet; 

import java.util.Set; 

public class Course { 

 private Integer id; 

 private String content; 

 //不同课程可以被不同的学生学习(多对多) 

 //当前课程可以被【多个学生】学习 

 private Set Student studentSet = new HashSet Student 

 public Integer getId() { 

 return id; 

 public void setId(Integer id) { 

 this.id = id; 

 public String getContent() { 

 return content; 

 public void setContent(String content) { 

 this.content = content; 

 public Set Student getStudentSet() { 

 return studentSet; 

 public void setStudentSet(Set Student studentSet) { 

 this.studentSet = studentSet; 

Course.hbm.xml

 ?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 

 class name="com.my.bean.Course" table="t_course" 

 id name="id" 

 generator /generator 

 /id 

 property name="content" /property 

 !-- 不同课程可以被不同的学生学习(多对多), 当前课程可以被【多个学生】学习 

 * 1 集合 # 中间表表名 

 * 2 中间表中外键名称 

 * 3 类型：另一个外键名称 

 set name="studentSet" table="t_student_course" !-- cascade="delete" -- 

 key column="course_id" /key 

 many-to-many column="student_id" /many-to-many 

 /set 

 /class 

 /hibernate-mapping 

测试类：

package com.my.bean; 

import org.hibernate.Session; 

import org.hibernate.SessionFactory; 

import org.hibernate.Transaction; 

import org.hibernate.cfg.Configuration; 

import org.junit.Test; 

public class TestManyToMany { 

 private SessionFactory factory = new Configuration() 

 .configure() 

 .addClass(Student.class) 

 .addClass(Course.class) 

 .buildSessionFactory(); 

 @Test 

 public void demo01(){ 

 Session session = factory.openSession(); 

 session.close(); 

 @Test 

 public void demo02(){ 

 // 保存 学生 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = new Student(); 

 student.setName("jack"); 

 session.save(student); 

 transaction.commit(); 

 session.close(); 

 @Test 

 public void demo03(){ 

 // 保存 课程 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Course course = new Course(); 

 course.setContent("java web"); 

 session.save(course); 

 transaction.commit(); 

 session.close(); 

 @Test 

 public void demo04(){ 

 // 保存学生 ，学生关联课程 -- 抛异常 (需要保存课程) 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = new Student(); 

 student.setName("rose"); 

 Course course = new Course(); 

 course.setContent("java 基础"); 

 //关系 

 student.getCourseSet().add(course); 

 session.save(course); 

 session.save(student); 

 transaction.commit(); 

 session.close(); 

 @Test 

 public void demo05(){ 

 /* 保存学生 ，学生关联课程 

 * 自动保存：学生在保存时，课程一并保存，需要在Student.hbm.xml配置 cascade="save-update" 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = new Student(); 

 student.setName("tom"); 

 Course course = new Course(); 

 course.setContent("java ssh"); 

 //关系 

 student.getCourseSet().add(course); 

 session.save(course); 

 session.save(student); 

 transaction.commit(); 

 session.close(); 


 /* 默认情况：当删除学生时，先将中间表的数据删除 

 * 级联删除：在删除学生时，先删除中间表的数据，级联删除课程内容 

 * Student.htm.xml 配置 , cascade="save-update,delete" 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = (Student) session.get(Student.class, 5); 

 session.delete(student); 

 transaction.commit(); 

 session.close(); 

 @Test 

 public void demo07(){ 

 //准备数据 demo08 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = new Student(); 

 student.setName("jack"); 

 Student student2 = new Student(); 

 student2.setName("tom"); 

 Student student3 = new Student(); 

 student3.setName("rose"); 


 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = (Student) session.get(Student.class, 4); 

 session.delete(student); 

 transaction.commit(); 

 session.close(); 

 @Test 

 public void demo09(){ 

 /* 前提：没有其他的配置 

 * 查询学生，查询课程，将当前课程从学生的选课中移除 

 * * 将中间表的数据进行删除 

 Session session = factory.openSession(); 

 Transaction transaction = session.beginTransaction(); 

 Student student = (Student) session.get(Student.class, 7); 

 Course course = (Course) session.get(Course. class, 4); 

 student.getCourseSet().remove(course); 

 transaction.commit(); 

 session.close(); 

注意
1 默认：当删除学生时，先将中间表的数据删除。（中间表的数据删除时，不会影响另一个多表的数据）
2 默认：取消关联关系时，将中间表的数据删除
student.getCourseSet().remove(course);
关联关系，cascade=”all|none|save-update|delete|all-delete-orphan|delete-orphan”
none ： 没有关系
save-update : 如果需要保存则进行保存，如果需要更新则进行更新，执行saveOrUpdate()
delete : 级联删除
delete-orphan ： 孤儿删除 （1对多）
all 除了孤儿删除其他都支持
all-delete-orphan 所有级联

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