Hibernate关系映射之多对多映射的两种方式

小鱼儿 2022-07-13 00:25 182阅读 0赞

## **多对多关系**\#\# ##

many-to-many  
应用场景：不建议使用，建议拆解成两个“一对多”连接  
关系定义（主控方）：

//xml映射方法
    <set name="propertyName" table="middle_table_name">
        <key column="columnName_master" />
        <many-to-many class="className" column="columnName_slave" />
    </set>
    
    //annotation注解映射方法
    @ManyToMany
    @JoinTable(name="middle_table_name"
        joinColumns=@JoinColumn(name="columnName_master",   
        inverseJoinColumns=@JoinColumn(name="columnName_slave"))
    )

关系定义（被控方）

//xml映射
    <set name="propertyName" table="middle_table_name">
        <key column="columnName_slave" />
        <many-to-many class="className" column="columnName_master" />
    </key>
    //annotation注解映射
    @ManyToMany(mappedBy="propertyName")

## **多对多映射代码**\#\# ##

说明：学生与学生之间的关系是多对多，一个学生可以对应多个教师，一个教师也可以对应多个学生。这里定义一个学生类Student和一个教师类Lecturer。  
一.xml映射  
1.新建Student.hbm.xml文件，在该文件里编写映射关系，Student为主控方。

<?xml version="1.0" encoding="UTF-8"?>
    <!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.ffy.studentmanage.Student" table="student">
            <id name="id" column="id">
                <generator class="assigned"></generator>
            </id>
            <property name="sid" column="sid"></property>
            <property name="firstName" column="firstname"></property>
            <property name="lastName" column="lastname"></property>
            <property name="gender" column="gender"></property>
            <property name="phone" column="phone"></property>
            <property name="email" column="email"></property>
            <property name="dateOfBirth" column="date_of_birth"></property>
            //一个学生可以有多个老师，所以需要用集合来放教师类。
            //name:在student类中有一个存放类型为Lecturer的集合，这里的name为该set。table:学生和教师关系的中间表名称
            <set name="lecturers" table="student_has_teacher">
            //column:中间表的用于与student（我方）关联的外键。
                <key column="student_id"></key>
            //column:中间表的用于与lecturer（对方）关联的外键。  class：表示对方的类
                <many-to-many column="lecturer_id" class="com.ffy.studentmanage.Lecture"></many-to-many>
            </set>
        </class>
    </hibernate-mapping>

2.新建Leturer.hbm.xml(对方)，填写映射关系

3.在hibernate.cfg.xml中注册上面两个xml文件。

二.annotation注解映射  
1.在hibernate.cfg.xml中注册Student.class类和Lecturer.class类。

2.在Student.class类里面添加注解。

package com.ffy.studentmanage;
    
    
    import java.util.Set;
    
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.JoinTable;
    import javax.persistence.ManyToMany;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="student")
    public class Student { 
        @Id
        @Column(name="id")
        private int id;
        @Column(name="sid")
        private int sid;
        @Column(name="firstname")
        private String firstName;
        @Column(name="lastname")
        private String lastName;
        @Column(name="gender")
        private String gender;
        @Column(name="phone")
        private String phone;
        @Column(name="email")
        private String email;
        @Column(name="date_of_birth")
        private String dateOfBirth;
        @Column(name="height")
        private double height；
    
        //声明多对多关系
        @ManyToMany
        @JoinTable(name="student_has_teacher",
            joinColumns=@JoinColumn(name="student_id"),
            inverseJoinColumns=@JoinColumn(name="lecturer_id"))
        private Set<Lecture> lecturers;
    
        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        public int getSid() {
            return sid;
        }
        public void setSid(int sid) {
            this.sid = sid;
        }
        public String getFirstName() {
            return firstName;
        }
        public void setFirstName(String firstName) {
            this.firstName = firstName;
        }
        public String getLastname() {
            return lastName;
        }
        public void setLastname(String lastName) {
            this.lastName = lastName;
        }
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
        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;
        }
        public String getDateOfBirth() {
            return dateOfBirth;
        }
        public void setDateOfBirth(String dateOfBirth) {
            this.dateOfBirth = dateOfBirth;
        }
        public double getHeight() {
            return height;
        }
        public void setHeight(double height) {
            this.height = height;
        }
        public String getLastName() {
            return lastName;
        }
        public void setLastName(String lastName) {
            this.lastName = lastName;
        }
        public Set<Lecture> getLecturers() {
            return lecturers;
        }
        public void setLecturers(Set<Lecture> lecturers) {
            this.lecturers = lecturers;
        }
    // public String toString(){ 
    // return this.id+":"+this.lastName+this.firstName+this.gender+":"+this.phone+":"+this.email+";username"+studentLogin.getUsername()+";password:"+studentLogin.getPassword();
    // }
    }

3.在Lecturer.class里面添加注解

package com.ffy.studentmanage;
    
    import java.util.Set;
    
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.ManyToMany;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="lecturer")
    public class Lecture { 
        @Id
        @Column(name="id")
        private int id;
        @Column(name="uid")
        private String uid;
        @Column(name="firstname")
        private String firstName;
        @Column(name="lastname")
        private String lastName;
        @Column(name="phone")
        private String phone;
        @Column(name="college_id")
        private int collegeId;
    
        //将权限交由对方，即Student.class。主控方与被控方通过主控方里的lecturers属性建立联系。
        @ManyToMany(mappedBy="lecturers")
        private Set<Student> students;
    
        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        public String getUid() {
            return uid;
        }
        public void setUid(String uid) {
            this.uid = uid;
        }
        public String getFirstName() {
            return firstName;
        }
        public void setFirstName(String firstName) {
            this.firstName = firstName;
        }
        public String getLastName() {
            return lastName;
        }
        public void setLastName(String lastName) {
            this.lastName = lastName;
        }
        public String getPhone() {
            return phone;
        }
        public void setPhone(String phone) {
            this.phone = phone;
        }
        public int getCollegeId() {
            return collegeId;
        }
        public void setCollegeId(int collegeId) {
            this.collegeId = collegeId;
        }
        public Set<Student> getStudents() {
            return students;
        }
        public void setStudents(Set<Student> students) {
            this.students = students;
        }
    
    }