Hibernate一對多、多對一的關係表達
阿新 • • 發佈：2019-11-13
一、關係表達：
1、一對多、多對一表的關係：
學生表：
班級表：
在學生表中，學生的學號是主鍵。在班級表中，班級號是主鍵，因此，學生表的外來鍵是classno。因此，班級對應學生是一對多，學生對應班級是多對一。因為，一個班級可以有多個學生，但是一個學生只能在一個班級。
2、物件的一對多、多對一關係：
（1）在Class類中，定義Set集合，表達一對多的關係：
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集合表達一對多關係
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(){//無參的構造方法
}
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）定義學生和班級的關係：
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集合表達一對多關係
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、配置對映檔案：
Class.hbm.xml：
（1）實現一對多的關係對映，即：一個班級對應多個學生：
<?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="pers.zhb.domain">
<class name="Clas" table="class">
<id name="classno" column="classno">
<generator class="native"></generator>
</id><!--主鍵-->
<property name="department" column="department"></property>
<property name="monitor" column="monitor"></property>
<property name="classname" column="classname"></property>
<set name="students" table="student"><!--一對多關係配置-->
<key column="classno" update="false"></key><!--指定了集合表的外來鍵-->
<one-to-many class="Student"></one-to-many>
</set>
</class>
</hibernate-mapping>
<set name="students">
指定對映的儲存學生的集合的名字。
<key column="classesno"></key>
對映的class表的外來鍵。
<one-to-many class="Student"></one-to-many>
指定學生的型別。
（2）實現多對一的關係對映，即：多個學生對應一個班級。
<?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="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屬性：對映的班級。
column屬性：對映的班級物件對應的外來鍵。
class屬性：指定班級的型別。
4、主配置檔案：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<!--配置資料庫資訊-必須的-->
<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資訊-可選的-->
<property name="hibernate.show_sql">true</property><!--輸出底層sql語句-->
<property name="hibernate.format_sql">true</property><!--格式化輸出sql語句-->
<property name="hibernate.hbm2ddl.auto">update</property><!--hibernate幫助建立表，如果已經有表更新表，如果沒有則建立新表-->
<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
<property name="hibernate.connection.isolation">4</property>
<!--指定session與當前執行緒繫結-->
<property name="hibernate.current_session_context_class">thread</property>
<!--配置資料庫的方言，讓hibernate識別框架自己的特有語句-->
<!--把對映檔案放到核心配置檔案-->
<mapping resource="pers/zhb/domain/Student.hbm.xml"/><!--都在src目錄下-->
<mapping resource="pers/zhb/domain/Class.hbm.xml"/><!--都在src目錄下-->
</session-factory>
</hibernate-configuration>
二、具體運用：
1、增加：
（1）建立一個新班級併為新班級新增兩名學生：
public class Test {
public static void testSel() {
Session session = HibernateUtils.openSession();//獲得session
Transaction transaction = session.beginTransaction();//開啟事務
Clas clas=new Clas();
clas.setClassname("計科171");
clas.setClassno(4600);
clas.setDepartment("一號樓");
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("[email protected]");
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("[email protected]");
clas.getStudents().add(student);//一對多，一個班級下有多個學生
clas.getStudents().add(student1);//獲取Set集合物件並向其中新增元素
student.setaClas(clas);//多對一，學生屬於哪一個班級
student1.setaClas(clas);
session.save(clas);
session.save(student);
session.save(student1);
transaction.commit();//提交事務
session.close();//關閉資源
}
（2）為一個已經存在的班級新增學生：
public static void testAdd(){
Session session = HibernateUtils.openSession();//獲得session
Transaction transaction = session.beginTransaction();//開啟事務
Clas clas=session.get(Clas.class,80501);//獲得一個已經存在的班級
Student student=new Student();//建立一個學生物件
student.setSname("翟zz");
student.setStudentno(20190000);
student.setPoint(133f);
student.setSex("男");
student.setBirthday("2019-11-16");
student.setPhone("18739496522");
student.setEmail("[email protected]");
Student student1=new Student();//再建立一個學生物件
student1.setSname("翟zz");
student1.setStudentno(20190000);
student1.setPoint(133f);
student1.setSex("男");
student1.setBirthday("2019-11-16");
student1.setPhone("18739496522");
student1.setEmail("[email protected]");
clas.getStudents().add(student);//學生新增到班級
student.setaClas(clas);//班級與學生對應
clas.getStudents().add(student1);
student1.setaClas(clas);
session.save(student);
session.save(student1);
transaction.commit();//提交事務
session.close();//關閉資源
}
2、刪除：
刪除80501班的一名學生資訊：
public static void testDel() {
Session session = HibernateUtils.openSession();//獲得session
Transaction transaction = session.beginTransaction();//開啟事務
Clas clas=session.get(Clas.class,80501);//獲得要刪除的學生屬於那一個班級
Student student=session.get(Student.class,937221532);//獲得要刪除的學生
clas.getStudents().remove(student);
student.setaClas(null);
transaction.commit();//提交事務
session.close();//關閉資源
}
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