Hibernate关系映射之多对多映射的两种方式-蒲公英云

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

<?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.Lecture" table="lecturer">
        <id name="id" column="id">
            <generator class="assigned"></generator>
        </id>
        <property name="uid" column="uid"></property>
        <property name="firstName" column="firstname"></property>
        <property name="lastName" column="lastname"></property>
        <property name="phone" column="phone"></property>
        <property name="collegeId" column="college_id"></property>
        //与上一步类似
        <set name="students" table="student_has_teacher">
            <key column="lecturer_id"></key>
            <many-to-many column="student_id" class="com.ffy.studentmanage.Student"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

3.在hibernate.cfg.xml中注册上面两个xml文件。

<mapping resource="Student.hbm.xml"/>
<mapping resource="Lecturer.hbm.xml"/>

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

<mapping class="com.ffy.studentmanage.Student"/> 
<mapping class="com.ffy.studentmanage.Lecture"/>

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;
    }
}