Hibernate一对多、多对一的关系表达
怀梦想，致远方 人气:1一、关系表达：
1、一对多、多对一表的关系：
学生表：
班级表：
在学生表中，学生的学号是主键。在班级表中，班级号是主键，因此，学生表的外键是classno。因此，班级对应学生是一对多，学生对应班级是多对一。因为，一个班级可以有多个学生，但是一个学生只能在一个班级。
2、对象的一对多、多对一关系：
（1）在Class类中，定义Set集合，表达一对多的关系：
package pers.zhb.domain;
import java.util.HashSet;
import java.util.Set;
public class Class {
private String classno;
private String department;
private String monitor;
private String classname;
private Set<Student> classes=new HashSet<Student>();//使用set集合表达一对多关系
public Class(){
}
public Set<Student> getClasses() {
return classes;
}
public void setClasses(Set<Student> classes) {
this.classes = classes;
}
public String getMonitor() {
return monitor;
}
public void setMonitor(String monitor) {
this.monitor = monitor;
}
public String getDepartment() {
return department;
}
public void setDepartment(String department) {
this.department = department;
}
public String getClassname() {
return classname;
}
public void setClassname(String classname) {
this.classname = classname;
}
public String getClassno() {
return classno;
}
public void setClassno(String classno) {
this.classno = classno;
}
@Override
public String toString() {
return "Class{" +
"classno='" + classno + '\'' +
", department='" + department + '\'' +
", monitor='" + monitor + '\'' +
", classname='" + classname + '\'' +
", classes=" + classes +
'}';
}
}
package pers.zhb.domain;
public class Student {
private Integer studentno;
private String sname;
private String sex;
private String birthday;
private String classno;
private Float point;
private String phone;
private String email;
private Clas aClas;
public Student(){//无参的构造方法
}
public Clas getaClas() {
return aClas;
}
public void setaClas(Clas aClas) {
this.aClas = aClas;
}
@Override
public String toString() {
return "Student{" +
"studentno='" + studentno + '\'' +
", sname='" + sname + '\'' +
", sex='" + sex + '\'' +
", birthday='" + birthday + '\'' +
", classno='" + classno + '\'' +
", point=" + point +
", phone='" + phone + '\'' +
", email='" + email + '\'' +
'}';
}
public int getStudentno() {
return studentno;
}
public void setStudentno(int studentno) {
this.studentno = studentno;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getBirthday() {
return birthday;
}
public void setBirthday(String birthday) {
this.birthday = birthday;
}
public String getClassno() {
return classno;
}
public void setClassno(String classno) {
this.classno = classno;
}
public float getPoint() {
return point;
}
public void setPoint(float point) {
this.point = point;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
（2）定义学生和班级的关系：
package pers.zhb.domain;
import java.util.HashSet;
import java.util.Set;
public class Clas {
private String classno;
private String department;
private String monitor;
private String classname;
private Set<Student> students=new HashSet<Student>();//使用set集合表达一对多关系
public Clas(){
}
public Set<Student> getStudents() {
return students;
}
public void setClasses(Set<Student> students) {
this.students = students;
}
public String getMonitor() {
return monitor;
}
public void setMonitor(String monitor) {
this.monitor = monitor;
}
public String getDepartment() {
return department;
}
public void setDepartment(String department) {
this.department = department;
}
public String getClassname() {
return classname;
}
public void setClassname(String classname) {
this.classname = classname;
}
public String getClassno() {
return classno;
}
public void setClassno(String classno) {
this.classno = classno;
}
@Override
public String toString() {
return "Class{" +
"classno='" + classno + '\'' +
", department='" + department + '\'' +
", monitor='" + monitor + '\'' +
", classname='" + classname + '\'' +
",students=" + students +
'}';
}
}
3、配置映射文件：
Class.hbm.xml：
（1）实现一对多的关系映射，即：一个班级对应多个学生：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.orghttps://img.qb5200.com/download-x/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Clas" table="class">
<id name="classno" column="classno">
<generator class="native"></generator>
</id><!--主键-->
<property name="department" column="department"></property>
<property name="monitor" column="monitor"></property>
<property name="classname" column="classname"></property>
<set name="students" table="student"><!--一对多关系配置-->
<key column="classno" update="false"></key><!--指定了集合表的外键-->
<one-to-many class="Student"></one-to-many>
</set>
</class>
</hibernate-mapping>
<set name="students">
指定映射的存储学生的集合的名字。
<key column="classesno"></key>
映射的class表的外键。
<one-to-many class="Student"></one-to-many>
指定学生的类型。
（2）实现多对一的关系映射，即：多个学生对应一个班级。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.orghttps://img.qb5200.com/download-x/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Student" table="student">
<id name="studentno" column="studentno" >
<generator class="native"></generator>
</id>
<property name="birthday" column="birthday"></property>
<property name="classno" column="classno" insert="false" update="false"></property>
<property name="email" column="email"></property>
<property name="phone" column="phone"></property>
<property name="sex" column="sex"></property>
<property name="sname" column="sname"></property>
<property name="point" column="point"></property>
<many-to-one name="aClas" column="classno" class="Clas"></many-to-one>
</class>
</hibernate-mapping>
name属性：映射的班级。
column属性：映射的班级对象对应的外键。
class属性：指定班级的类型。
4、主配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.orghttps://img.qb5200.com/download-x/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<!--配置数据库信息-必须的-->
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/stu_mangement</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<!--配置hibernate信息-可选的-->
<property name="hibernate.show_sql">true</property><!--输出底层sql语句-->
<property name="hibernate.format_sql">true</property><!--格式化输出sql语句-->
<property name="hibernate.hbm2ddl.auto">update</property><!--hibernate帮助创建表，如果已经有表更新表，如果没有则创建新表-->
<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
<property name="hibernate.connection.isolation">4</property>
<!--指定session与当前线程绑定-->
<property name="hibernate.current_session_context_class">thread</property>
<!--配置数据库的方言，让hibernate识别框架自己的特有语句-->
<!--把映射文件放到核心配置文件-->
<mapping resource="pers/zhbhttps://img.qb5200.com/download-x/domain/Student.hbm.xml"/><!--都在src目录下-->
<mapping resource="pers/zhbhttps://img.qb5200.com/download-x/domain/Class.hbm.xml"/><!--都在src目录下-->
</session-factory>
</hibernate-configuration>
二、具体运用：
1、增加：
（1）创建一个新班级并为新班级添加两名学生：
public class Test {
public static void testSel() {
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Clas clas=new Clas();
clas.setClassname("计科171");
clas.setClassno(4600);
clas.setDepartment("一号楼");
clas.setMonitor("zhai");
Student student=new Student();
student.setSname("翟");
student.setStudentno(2017151411);
student.setPoint(123f);
student.setSex("男");
student.setBirthday("2019-11-11");
student.setPhone("18739496522");
student.setClassno("221221");
student.setEmail("34288334@qq.com");
Student student1=new Student();
student1.setSname("翟hb");
student1.setStudentno(2017151419);
student1.setPoint(666f);
student1.setSex("女");
student1.setBirthday("2019-11-11");
student1.setPhone("18739496522");
student1.setClassno("221221");
student1.setEmail("34288334@qq.com");
clas.getStudents().add(student);//一对多，一个班级下有多个学生
clas.getStudents().add(student1);//获取Set集合对象并向其中添加元素
student.setaClas(clas);//多对一，学生属于哪一个班级
student1.setaClas(clas);
session.save(clas);
session.save(student);
session.save(student1);
transaction.commit();//提交事务
session.close();//关闭资源
}
（2）为一个已经存在的班级添加学生：
public static void testAdd(){
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Clas clas=session.get(Clas.class,80501);//获得一个已经存在的班级
Student student=new Student();//创建一个学生对象
student.setSname("翟zz");
student.setStudentno(20190000);
student.setPoint(133f);
student.setSex("男");
student.setBirthday("2019-11-16");
student.setPhone("18739496522");
student.setEmail("34288334@qq.com");
Student student1=new Student();//再创建一个学生对象
student1.setSname("翟zz");
student1.setStudentno(20190000);
student1.setPoint(133f);
student1.setSex("男");
student1.setBirthday("2019-11-16");
student1.setPhone("18739496522");
student1.setEmail("34288334@qq.com");
clas.getStudents().add(student);//学生添加到班级
student.setaClas(clas);//班级与学生对应
clas.getStudents().add(student1);
student1.setaClas(clas);
session.save(student);
session.save(student1);
transaction.commit();//提交事务
session.close();//关闭资源
}
2、删除：
删除80501班的一名学生信息：
public static void testDel() {
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Clas clas=session.get(Clas.class,80501);//获得要删除的学生属于那一个班级
Student student=session.get(Student.class,937221532);//获得要删除的学生
clas.getStudents().remove(student);
student.setaClas(null);
transaction.commit();//提交事务
session.close();//关闭资源
}
加载全部内容