多對多關係##

many-to-many
應用場景：不建議使用，建議拆解成兩個“一對多”連線
關係定義（主控方）：

//xml對映方法
<set name="propertyName" table="middle_table_name">
    <key column="columnName_master" />
    <many-to-many class="className" column="columnName_slave" />
</set>

//annotation註解對映方法
@ManyToMany
@JoinTable(name="middle_table_name"
 

    joinColumns=@JoinColumn(name="columnName_master",   
    inverseJoinColumns=@JoinColumn(name="columnName_slave"))
)

關係定義（被控方）

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

多對多對映程式碼##

說明：學生與學生之間的關係是多對多，一個學生可以對應多個教師，一個教師也可以對應多個學生。這裡定義一個學生類Student和一個教師類Lecturer。
一.xml對映
1.新建Student.hbm.xml檔案，在該檔案裡編寫對映關係，Student為主控方。

<?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>
        //一個學生可以有多個老師，所以需要用集合來放教師類。
        //name:在student類中有一個存放型別為Lecturer的集合，這裡的name為該set。table:學生和教師關係的中間表名稱
        <set name="lecturers" table="student_has_teacher">
        //column:中間表的用於與student（我方）關聯的外來鍵。
            <key column="student_id"></key>
        //column:中間表的用於與lecturer（對方）關聯的外來鍵。  class：表示對方的類
            <many-to-many column="lecturer_id" class="com.ffy.studentmanage.Lecture"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

2.新建Leturer.hbm.xml(對方)，填寫對映關係

<?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>
        //與上一步類似
        <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中註冊上面兩個xml檔案。

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

二.annotation註解對映
1.在hibernate.cfg.xml中註冊Student.class類和Lecturer.class類。

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

2.在Student.class類裡面添加註解。

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；

    //宣告多對多關係
    @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裡面添加註解

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;

    //將許可權交由對方，即Student.class。主控方與被控方通過主控方里的lecturers屬性建立聯絡。
    @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;
    }

}