多对多关系
创建实体类和对应映射文件
Student.java
1 package com.qf.entity; 2 ?3 import java.util.HashSet; 4 import java.util.Set; 5 ?6 public class Student { 7 ?8 ????private Long sid; 9 ????private String sname;10 ????//一个学生可以有很多个老师11 ????private Set<Teacher> teachs = new HashSet<>();12 13 ????public Long getSid() {14 ????????return sid;15 ????}16 ????public void setSid(Long sid) {17 ????????this.sid = sid;18 ????}19 ????20 ????public String getSname() {21 ????????return sname;22 ????}23 ????public void setSname(String sname) {24 ????????this.sname = sname;25 ????}26 ????27 ????public Set<Teacher> getTeachs() {28 ????????return teachs;29 ????}30 ????public void setTeachs(Set<Teacher> teachs) {31 ????????this.teachs = teachs;32 ????}33 ????@Override34 ????public String toString() {35 ????????return "Student [sid=" + sid + ", sname=" + sname + ", teachs=" + teachs + "]";36 ????}37 ????38 }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><!-- 配置表与实体的映射关系 --><class name="com.qf.entity.Student" table="student"><id name="sid" column="sid"><generator class="native"></generator></id><property name="sname" column="sname"/><set name="teachs" table="teach_stu" ><key column="sid"/><many-to-many class="com.qf.entity.Teacher" column="tid" /></set></class></hibernate-mapping>
Teacher.java
1 package com.qf.entity; 2 ?3 import java.util.HashSet; 4 import java.util.Set; 5 ?6 public class Teacher { 7 ????private long tid; 8 ????private String tname; 9 ????private String course;10 ????//一个教师可以有多个学生11 ????private Set<Student> stus = new HashSet<Student>();12 ????13 ????public Set<Student> getStus() {14 ????????return stus;15 ????}16 ????public void setStus(Set<Student> stus) {17 ????????this.stus = stus;18 ????}19 ????public long getTid() {20 ????????return tid;21 ????}22 ????public void setTid(long tid) {23 ????????this.tid = tid;24 ????}25 ????public String getTname() {26 ????????return tname;27 ????}28 ????public void setTname(String tname) {29 ????????this.tname = tname;30 ????}31 ????public String getCourse() {32 ????????return course;33 ????}34 ????public void setCourse(String course) {35 ????????this.course = course;36 ????}37 ????@Override38 ????public String toString() {39 ????????return "Teacher [tid=" + tid + ", tname=" + tname + ", course=" + course + "]";40 ????}41 ????42 ????43 }Teacher.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><!-- 配置表与实体的映射关系 --><class name="com.qf.entity.Teacher" table="teacher"><id name="tid" column="tid"><generator class="native"/></id><property name="tname" column="tname"/><property name="course" column="course"/><set name="stus" table="teach_stu"><key column="tid"></key><many-to-many class="com.qf.entity.Student" column="sid"/></set></class></hibernate-mapping>
测试
@Testpublic void test() {Session session = SessionFactoryUtil.getSession();Transaction tx = session.beginTransaction();//创建两个教师对象，三个学生对象//学生选择老师Teacher t1 = new Teacher();t1.setTname("张老师");Teacher t2 = new Teacher();t2.setTname("李老师");Student s1 = new Student();s1.setSname("张三");Student s2 = new Student();s2.setSname("李四");Student s3 = new Student();s3.setSname("王五");//学生和老师之间建立双向关系//多对多关系建立双向关系后，双方必须有一方放弃维护外键关系权（inverse），否则会因为中间表主键重复抛出异常s1.getTeachs().add(t1);s1.getTeachs().add(t2);s3.getTeachs().add(t1);s2.getTeachs().add(t2);t1.getStus().add(s1);t1.getStus().add(s3);t2.getStus().add(s2);t2.getStus().add(s1);session.save(s1);session.save(s2);session.save(s3);session.save(t1);session.save(t2);tx.commit();}-------------------------------------console-------------------------------------
Hibernate: alter table teach_stu drop foreign key FKsrw3nh8oe5xhmqqxm2qng952tHibernate: alter table teach_stu drop foreign key FKtc48sy6cweqkufd4c777i8vspHibernate: drop table if exists studentHibernate: drop table if exists teach_stuHibernate: drop table if exists teacherHibernate: create table student (sid bigint not null auto_increment, sname varchar(255), primary key (sid))Hibernate: create table teach_stu (tid bigint not null, sid bigint not null, primary key (sid, tid))Hibernate: create table teacher (tid bigint not null auto_increment, tname varchar(255), course varchar(255), primary key (tid))Hibernate: alter table teach_stu add constraint FKsrw3nh8oe5xhmqqxm2qng952t foreign key (sid) references student (sid)Hibernate: alter table teach_stu add constraint FKtc48sy6cweqkufd4c777i8vsp foreign key (tid) references teacher (tid)11:21:37,135 ?INFO SchemaExport:464 - HHH000230: Schema export completeHibernate: insert into student (sname) values (?)Hibernate: insert into student (sname) values (?)Hibernate: insert into student (sname) values (?)Hibernate: insert into teacher (tname, course) values (?, ?)Hibernate: insert into teacher (tname, course) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (tid, sid) values (?, ?)11:21:37,270 ?WARN SqlExceptionHelper:127 - SQL Error: 1062, SQLState: 2300011:21:37,271 ERROR SqlExceptionHelper:129 - Duplicate entry ‘1-1‘ for key ‘PRIMARY‘11:21:37,271 ?INFO AbstractBatchImpl:193 - HHH000010: On release of batch it still contained JDBC statements11:21:37,272 ERROR SessionImpl:2994 - HHH000346: Error during managed flush [could not execute statement]
原因
测试中因为建立了双向关系，所以teacher和student都会去维护外键，导致相同的（1，1）会两次插入中间关系表teach_stu中
解决办法
一方放弃维护外键关系权。一般被动主体放弃维护外键权，比如学生选择老师，老师放弃维护外键权；老师选择学生，学生放弃维护外键权
修改Teacher.hbm.xml：<set name="stus" table="teach_stu" inverse="true">
-------------------------------------console-------------------------------------
Hibernate: alter table teach_stu drop foreign key FKsrw3nh8oe5xhmqqxm2qng952tHibernate: alter table teach_stu drop foreign key FKtc48sy6cweqkufd4c777i8vspHibernate: drop table if exists studentHibernate: drop table if exists teach_stuHibernate: drop table if exists teacherHibernate: create table student (sid bigint not null auto_increment, sname varchar(255), primary key (sid))Hibernate: create table teach_stu (tid bigint not null, sid bigint not null, primary key (sid, tid))Hibernate: create table teacher (tid bigint not null auto_increment, tname varchar(255), course varchar(255), primary key (tid))Hibernate: alter table teach_stu add constraint FKsrw3nh8oe5xhmqqxm2qng952t foreign key (sid) references student (sid)Hibernate: alter table teach_stu add constraint FKtc48sy6cweqkufd4c777i8vsp foreign key (tid) references teacher (tid)11:30:43,077 ?INFO SchemaExport:464 - HHH000230: Schema export completeHibernate: insert into student (sname) values (?)Hibernate: insert into student (sname) values (?)Hibernate: insert into student (sname) values (?)Hibernate: insert into teacher (tname, course) values (?, ?)Hibernate: insert into teacher (tname, course) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?)
数据成功插入数据库
级联保存
保存学生级联保存教师
主体是学生，所以修改学生的映射文件Student.hbm.xml
<hibernate-mapping><!-- 配置表与实体的映射关系 --><class name="com.qf.entity.Student" table="student"><id name="sid" column="sid"><generator class="native"></generator></id><property name="sname" column="sname"/><set name="teachs" table="teach_stu" cascade="save-update" ><key column="sid"/><many-to-many class="com.qf.entity.Teacher" column="tid" /></set></class></hibernate-mapping>
测试方法
@Testpublic void test() {Session session = SessionFactoryUtil.getSession();Transaction tx = session.beginTransaction();//保存学生级联保存教师Teacher t1 = new Teacher();t1.setTname("张老师");Student s1 = new Student();s1.setSname("张三");t1.getStus().add(s1);s1.getTeachs().add(t1);session.save(s1);tx.commit();}-------------------------------------console-------------------------------------
Hibernate: create table student (sid bigint not null auto_increment, sname varchar(255), primary key (sid))Hibernate: create table teach_stu (tid bigint not null, sid bigint not null, primary key (sid, tid))Hibernate: create table teacher (tid bigint not null auto_increment, tname varchar(255), course varchar(255), primary key (tid))Hibernate: alter table teach_stu add constraint FKsrw3nh8oe5xhmqqxm2qng952t foreign key (sid) references student (sid)Hibernate: alter table teach_stu add constraint FKtc48sy6cweqkufd4c777i8vsp foreign key (tid) references teacher (tid)14:22:37,418 ?INFO SchemaExport:464 - HHH000230: Schema export completeHibernate: insert into student (sname) values (?)Hibernate: insert into teacher (tname, course) values (?, ?)Hibernate: insert into teach_stu (sid, tid) values (?, ?
级联删除（一般不使用）
想以哪一方为主体删除另一方，就在哪一方映射文件中配置cascade属性：
<set name="teachs" table="teach_stu" cascade="delete" >
六、hibernate表与表之间的关系（多对多关系）
原文地址：https://www.cnblogs.com/qf123/p/10173799.html