Hibernate(六)一对多映射(多对一)

一、Hinbernate中持久化类的关联关系

在数据库中，表表之间是通过外键关联的，在程序中是要转化为持久化类也就是(JAVA Bean)来实例的。

但在Hibernater中持久化的之间的映射关系，不是通外键建立关联，而是通过属性.主要有以下几种

• 一对一，
• 一对多(多对一)
• 多对多

关联方向：

• 单向关联
• 双向关联

二、一对多单向关联关系

2.1、建立数据库表

班级表，和学生表，学生生通过班级表中的，班级编号为外键

--班级表
create table grade
(
       gid       number           primary key,  --班级ID
       gname     varchar2(50),                  --班级名称
       gdesc     varchar2(50)                   --班级介绍
);
--学生表
create table student
(
       sid       number           primary key,  --主键ID学生ID
       sname     varchar2(20),            --学生姓名
       sex       varchar2(20),            --学生性别
       gid       number           references grade(gid) ---外键班级ID
);

2.2、建立持久化类和映射配置文件

班级和学生类

package entity;


import java.util.HashSet;
import java.util.Set;


/*
 * 班级类
 */
public class Grade implements java.io.Serializable {

    // Fields
    private static final long serialVersionUID = 1L;
    private int gid;
    private String gname;
    private String gdesc;
    private Set<Student> students = new HashSet<Student> ();

    // Constructors

    /** default constructor */
    public Grade() {
    }

    /** minimal constructor */
    public Grade(int gid) {
        this.gid = gid;
    }

    /** full constructor */
    public Grade(int gid, String gname, String gdesc, Set<Student> students) {
        this.gid = gid;
        this.gname = gname;
        this.gdesc = gdesc;
        this.students = students;
    }

    // Property accessors

    public int getGid() {
        return this.gid;
    }

    public void setGid(int gid) {
        this.gid = gid;
    }

    public String getGname() {
        return this.gname;
    }

    public void setGname(String gname) {
        this.gname = gname;
    }

    public String getGdesc() {
        return this.gdesc;
    }

    public void setGdesc(String gdesc) {
        this.gdesc = gdesc;
    }

    public Set<Student> getStudents() {
        return this.students;
    }

    public void setStudents(Set<Student> students) {
        this.students = students;
    }

}

 

学生类

package entity;

/*
 * 学生类
 */
public class Student implements java.io.Serializable {

    // Fields

    private static final long serialVersionUID = 1L;
    private int sid;
    
    private String sname;
    private String sex;

    // Constructors

    /** default constructor */
    public Student() {
    }

    /** minimal constructor */
    public Student(int sid) {
        this.sid = sid;
    }

    /** full constructor */
    public Student(int sid, String sname, String sex ) {
    
        this.sid = sid;

        this.sname = sname;
        this.sex = sex;
    }

    // Property accessors

    public int getSid() {
        return this.sid;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    

    public String getSname() {
        return this.sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public String getSex() {
        return this.sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

}

 

 

hibernate.cf.xml和班级、学生的配置文件

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>
    <property name="dialect">
        org.hibernate.dialect.Oracle9Dialect
    </property>
    <property name="connection.url">
        jdbc:oracle:thin:@localhost:1521:orcl
    </property>
    <property name="connection.username">root</property>
    <property name="connection.password">root</property>
    <property name="connection.driver_class">
        oracle.jdbc.OracleDriver
    </property>
    <property name="show_sql">true</property>
    <property name="format_sql">true</property>

    <mapping resource="entity/Grade.hbm.xml" />
    <mapping resource="entity/Student.hbm.xml" />

</session-factory>

</hibernate-configuration>

持久类配置先来学生类

<?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="entity.Student" table="STUDENT" schema="ROOT">
        <id name="sid" type="java.lang.Integer">
            <column name="SID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="sname" type="java.lang.String">
            <column name="SNAME" length="20" />
        </property>
        <property name="sex" type="java.lang.String">
            <column name="SEX" length="20" />
        </property>
    </class>
</hibernate-mapping>

班级类配置

<?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="entity.Grade" table="GRADE" schema="ROOT">
        <id name="gid" type="java.lang.Integer">
            <column name="GID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="gname" type="java.lang.String">
            <column name="GNAME" length="50" />
        </property>
        <property name="gdesc" type="java.lang.String">
            <column name="GDESC" length="50" />
        </property>
        <!--建立set属性，也可以建立list和持久化类中一致就行  -->
        <set name="students">
            <key>
            <!--这里的列是指学生表中的班级编号  -->
                <column name="GID" precision="22" scale="0" />
            </key>
            <!-- 通过class属性指定set的属性 -->
            <one-to-many class="entity.Student" />
        </set>
    </class>
</hibernate-mapping>

测试类

package Test;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

public class Demo1 {

    /**
     * 测试类
     */
    public static void main(String[] args) {
        save();
         find();
        update();

    }

    public static void save() {
        // 声明班级对象，并赋值
        Grade grade = new Grade();
        grade.setGid(201504);
        grade.setGname("Java一班");
        grade.setGdesc("刚开始学习JAVA");
        // 声明2个学生对象
        Student stu1 = new Student();
        stu1.setSid(201504012);
        stu1.setSname("张三");
        stu1.setSex("男");

        Student stu2 = new Student();
        stu2.setSid(201504013);
        stu2.setSname("李四");
        stu2.setSex("女");

        // 将学生添加到班级
        grade.getStudents().add(stu1);
        grade.getStudents().add(stu2);
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
        // 保存班级
        session.save(grade);
        // 保存学生
        session.save(stu1);
        session.save(stu2);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }

    /*
     * 将基中一个学生更改为别一个班级
     */
    public static void update() {
        // 声明班级对象，并赋值
        Grade grade = new Grade();
        grade.setGid(201506);
        grade.setGname("Java二班");
        grade.setGdesc("学习JAVA二年级");
        // 获取一个学生的信息
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
        Student stu1=(Student) session.get(Student.class, 201504013);
        //将学生添加到这个新的班级
        grade.getStudents().add(stu1);
        // 保存班级
        session.save(grade);
        // 保存学生
        session.save(stu1);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }

    // 查询班级
    public static void find() {

        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        Grade g = (Grade) session.get(Grade.class, 201504);
        System.out.println("班级信息：" + g.getGid() + "\t" + g.getGname()
                + g.getGdesc());
        // 通过班级获取这个班级的学生信息
        System.out.println("201504班的学生信息如下:");
        Set<Student> set = g.getStudents();
        for (Student stu : set) {
            System.out.println(stu.getSid() + "\t" + stu.getSname() + "\t"
                    + stu.getSex());
        }
    }

}

以上只上单向关联，一般都会有双向关联

同样要在学生类中添加Grade 属性

在学生类的配置文件中配置关联字段

 二、建立双向关联

2.1、更改学生类和配置文件

package entity;

/*
 * 学生类
 */
public class Student implements java.io.Serializable {

    // Fields

    private static final long serialVersionUID = 1L;
    private int sid;
    private String sname;
    private String sex;
    //增加班级属性
    private Grade grade;

    // Constructors

    /** default constructor */
    public Student() {
    }

    /** minimal constructor */
    public Student(int sid) {
        this.sid = sid;
    }

    /** full constructor */
    public Student(int sid, String sname, String sex ) {
    
        this.sid = sid;

        this.sname = sname;
        this.sex = sex;
    }

    // Property accessors

    public int getSid() {
        return this.sid;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    

    public String getSname() {
        return this.sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public String getSex() {
        return this.sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Grade getGrade() {
        return grade;
    }

    public void setGrade(Grade grade) {
        this.grade = grade;
    }
    

}

配置文件 

<?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="entity.Student" table="STUDENT" schema="ROOT">
        <id name="sid" type="java.lang.Integer">
            <column name="SID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="sname" type="java.lang.String">
            <column name="SNAME" length="20" />
        </property>
        <property name="sex" type="java.lang.String">
            <column name="SEX" length="20" />
        </property>
        <!--配置grade属性  -->
        <many-to-one name="grade" class="entity.Grade">
        <!--指定学生表中的外键  -->
        <column name="GID" />
        </many-to-one>
    </class>
</hibernate-mapping>

2.2、测试类

建立双向关联后，就可以通过学生来获取班级信息

清空数据表中的数据

package Test;

import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

import entity.Student;

public class Demo2 {

    /**
     * 测试类
     */
    public static void main(String[] args) {
　save();
findByStu();
    }
    
    public static void findByStu(){
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        //获取一个学生的信息 get方法为通过主键查询
        Student stu=(Student) session.get(Student.class, 201504013);
        System.out.println("学生信息:\t"+stu.getSid()+"\t"+stu.getSname()+"\t"+stu.getSex());
        //通过学生信息得到班级信息
        System.out.println("这个学生的班级信息："+stu.getGrade().getGid()+"\t"+stu.getGrade().getGname()+"\t"+stu.getGrade().getGdesc());
    }
}
public static void save() {
// 声明班级对象，并赋值
Grade grade = new Grade();
grade.setGid(201504);
grade.setGname("Java一班");
grade.setGdesc("刚开始学习JAVA");
// 声明2个学生对象
Student stu1 = new Student();
stu1.setSid(201504012);
stu1.setSname("张三");
stu1.setSex("男");
stu1.setGrade(grade);


Student stu2 = new Student();
stu2.setSid(201504013);
stu2.setSname("李四");
stu2.setSex("女");
stu2.setGrade(grade);
// 将学生添加到班级
/*grade.getStudents().add(stu1);
grade.getStudents().add(stu2);*/
// 建立session
Session session = new Configuration().configure().buildSessionFactory()
.openSession();
// 开始事务
Transaction transaction = session.beginTransaction();
// 保存班级
session.save(grade);
// 保存学生
session.save(stu1);
session.save(stu2);
// 提交事务
transaction.commit();
// 关闭session
session.close();
}

三、级联保存和删除

能不能只保存学生时，同时保存班级呢，或者保存班级时，同时保存学生呢

3.1、cascade属性

 

保存班级时，同时保存学生信息

修改班级配置，在set标签中添加cascade属性,设置为save-update

<?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="entity.Grade" table="GRADE" schema="ROOT">
        <id name="gid" type="java.lang.Integer">
            <column name="GID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="gname" type="java.lang.String">
            <column name="GNAME" length="50" />
        </property>
        <property name="gdesc" type="java.lang.String">
            <column name="GDESC" length="50" />
        </property>
        <!--建立set属性，也可以建立list和持久化类中一致就行  -->
        <set name="students" cascade="save-update">
            <key>
            <!--这里的列是指学生表中的班级编号  -->
                <column name="GID" precision="22" scale="0" />
            </key>
            <!-- 通过class属性指定set的属性 -->
            <one-to-many class="entity.Student" />
        </set>
    </class>
</hibernate-mapping>

测试类

package Test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

public class Demo3 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        save();

    }
    public static void save() {
        // 声明班级对象，并赋值
        Grade grade = new Grade();
        grade.setGid(201504);
        grade.setGname("Java一班");
        grade.setGdesc("刚开始学习JAVA");
        // 声明2个学生对象
        Student stu1 = new Student();
        stu1.setSid(201504012);
        stu1.setSname("张三");
        stu1.setSex("男");
        stu1.setGrade(grade);
        
        
        Student stu2 = new Student();
        stu2.setSid(201504013);
        stu2.setSname("李四");
        stu2.setSex("女");
        stu2.setGrade(grade);
        // 将学生添加到班级
        grade.getStudents().add(stu1);
        grade.getStudents().add(stu2);
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
        // 保存班级
        session.save(grade);
        // 保存学生
        //session.save(stu1);
        //session.save(stu2);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }
}

反之，在学生类的配置文件one-many中添加cascade属性设置为save-update

<?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="entity.Student" table="STUDENT" schema="ROOT">
        <id name="sid" type="java.lang.Integer">
            <column name="SID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="sname" type="java.lang.String">
            <column name="SNAME" length="20" />
        </property>
        <property name="sex" type="java.lang.String">
            <column name="SEX" length="20" />
        </property>
        <!--配置grade属性  -->
        <many-to-one name="grade" class="entity.Grade" cascade="save-update">
        <!--指定学生表中的外键  -->
        <column name="GID" />
        </many-to-one>
    </class>
</hibernate-mapping>

package Test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

public class Demo3 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        save();

    }
    public static void save() {
        // 声明班级对象，并赋值
        Grade grade = new Grade();
        grade.setGid(201504);
        grade.setGname("Java一班");
        grade.setGdesc("刚开始学习JAVA");
        // 声明2个学生对象
        Student stu1 = new Student();
        stu1.setSid(201504012);
        stu1.setSname("张三");
        stu1.setSex("男");
        stu1.setGrade(grade);
        
        
        Student stu2 = new Student();
        stu2.setSid(201504013);
        stu2.setSname("李四");
        stu2.setSex("女");
        stu2.setGrade(grade);
        // 将学生添加到班级
        grade.getStudents().add(stu1);
        grade.getStudents().add(stu2);
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
        // 保存班级
        //session.save(grade);
        // 保存学生
        session.save(stu1);
        session.save(stu2);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }
}

 

3.2、inverse属性

 

首先在班级类中设置invers属性为false时，删除班级

<?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="entity.Grade" table="GRADE" schema="ROOT">
        <id name="gid" type="java.lang.Integer">
            <column name="GID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="gname" type="java.lang.String">
            <column name="GNAME" length="50" />
        </property>
        <property name="gdesc" type="java.lang.String">
            <column name="GDESC" length="50" />
        </property>
        <!--建立set属性，也可以建立list和持久化类中一致就行  -->
        <set name="students" cascade="save-update" inverse="false">
            <key>
            <!--这里的列是指学生表中的班级编号  -->
                <column name="GID" precision="22" scale="0" />
            </key>
            <!-- 通过class属性指定set的属性 -->
            <one-to-many class="entity.Student" />
        </set>
    </class>
</hibernate-mapping>

测试类

package Test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

public class Demo4 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        delete() ;

    }

    public static void delete() {
        
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
        // 保存班级
        Grade grade=(Grade) session.get(Grade.class, 201504);
        // 保存学生
        session.delete(grade);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }
}

结果：发现班级表中的班级已经删除，而学生表中数据没有删除，只是GID字段为NULL

下面将inverse设置为true时，添加新学生，和新的班级

<?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="entity.Grade" table="GRADE" schema="ROOT">
        <id name="gid" type="java.lang.Integer">
            <column name="GID" precision="22" scale="0" />
            <generator class="assigned" />
        </id>
        <property name="gname" type="java.lang.String">
            <column name="GNAME" length="50" />
        </property>
        <property name="gdesc" type="java.lang.String">
            <column name="GDESC" length="50" />
        </property>
        <!--建立set属性，也可以建立list和持久化类中一致就行  -->
        <set name="students" cascade="save-update" inverse="true">
            <key>
            <!--这里的列是指学生表中的班级编号  -->
                <column name="GID" precision="22" scale="0" />
            </key>
            <!-- 通过class属性指定set的属性 -->
            <one-to-many class="entity.Student" />
        </set>
    </class>
</hibernate-mapping>

测试类

package Test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

public class Demo4 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        delete() ;

    }

    public static void delete() {
        
        // 声明班级对象，并赋值
                Grade grade = new Grade();
                grade.setGid(201509);
                grade.setGname("Java三班");
                grade.setGdesc("ASP.NET");
                // 声明2个学生对象
                Student stu1 = new Student();
                stu1.setSid(201509009);
                stu1.setSname("王五");
                stu1.setSex("女");
                stu1.setGrade(grade);
                
                Student stu2 = new Student();
                stu2.setSid(201509045);
                stu2.setSname("赵六");
                stu2.setSex("女");
                stu2.setGrade(grade);
        
        // 建立session
        Session session = new Configuration().configure().buildSessionFactory()
                .openSession();
        // 开始事务
        Transaction transaction = session.beginTransaction();
    
        
        // 保存学生
        session.save(stu1);
        session.save(stu2);
        // 提交事务
        transaction.commit();
        // 关闭session
        session.close();
    }
}

结果发现，我并没有用班级添加学生，也没有保存班级，只是保存了学生，班级信息一起保存了 

来源：https://www.cnblogs.com/liunanjava/p/4336126.html