Hibernate关联映射之一对多，多对一以及双向一对多

系统管理员 2022-09-25 05:15 206阅读 0赞

在上篇博客我们讲了hibernate对单表的操作，本篇博客就来讲讲对多表的关联映射操作。首先我们拿来做例子的表为班级表1---n学生表，在这次的测试主键我用的是序列，创建代码如下：

--班级表
    drop table classes;
    create table classes(
           cid int primary key,
           cname varchar2(50)
    );
    
    drop sequence seq_classes_cid;
    create sequence seq_classes_cid
           START WITH 1000    -- 从1000开始计数 
           INCREMENT BY 1     -- 每次加1个
    
    --学生表
    drop table student;
    create table student(
           sid int primary key,
           sname varchar2(50),
           cid int constraint FK_student_cid references classes(cid)
    );
    
    drop sequence seq_student_sId;
    create sequence seq_student_sId
           START WITH 1000    -- 从1000开始计数 
           INCREMENT BY 1     -- 每次加1个

对于使用hibernate我们都需要配置cfg文件，所以在此贴出我的cfg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="connection.username">hibernate</property>
    		<property name="connection.password">a</property>
    		<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
    		<property name="connection.url">jdbc:oracle:thin:@localhost:1521:orcl</property>
    		
    		<property name="dialect">org.hibernate.dialect.OracleDialect</property>
    
    		
    		<property name="show_sql">true</property>
    		
    		<property name="format_sql">true</property>
    		
    		<property name="hbm2ddl.auto">update</property>
    		
    		<property name="hibernate.current_session_context_class">thread</property>
    
    	</session-factory>
    </hibernate-configuration>

### 一对多的关联关系 ###

1.首先我们需要编写学生和班级的实体类

package com.yc.entity;
    
    import java.io.Serializable;
    
    public class Student implements Serializable{
    	private static final long serialVersionUID = 3914237588346266940L;
    
    	private int sid;
    	private String sname;
    
    	public Student() {
    	}
    	public Student(String sname) {
    		this.sname = sname;
    	}
    	public Student(int sid, String sname) {
    		this.sid = sid;
    		this.sname = sname;
    	}
    
    	public int getSid() {
    		return sid;
    	}
    	public void setSid(int sid) {
    		this.sid = sid;
    	}
    	public String getSname() {
    		return sname;
    	}
    	public void setSname(String sname) {
    		this.sname = sname;
    	}
    
    	public String toString() {
    		return "Student [sid=" + sid + ", sname=" + sname + "]";
    	}
    }

package com.yc.entity;
    
    import java.io.Serializable;
    import java.util.HashSet;
    import java.util.Set;
    
    public class Classes implements Serializable {
    	private static final long serialVersionUID = 948637569053708320L;
    
    	private int cid;
    	private String cname;
    	//在一方定义一个多方的集合 一对多
    	private Set<Student> students=new HashSet<Student>();
    
    	public Classes() {
    
    	}
    	public Classes(String cname) {
    		this.cname = cname;
    	}
    	public Classes(int cid, String cname, Set<Student> students) {
    		this.cid = cid;
    		this.cname = cname;
    		this.students = students;
    	}
    
    	public int getCid() {
    		return cid;
    	}
    	public void setCid(int cid) {
    		this.cid = cid;
    	}
    	public String getCname() {
    		return cname;
    	}
    	public void setCname(String cname) {
    		this.cname = cname;
    	}
    	public Set<Student> getStudents() {
    		return students;
    	}
    	public void setStudents(Set<Student> students) {
    		this.students = students;
    	}
    
    	public String toString() {
    		return "Classes [cid=" + cid + ", cname=" + cname + ", students="
    				+ students + "]";
    	}
    }

2.根据实体类创建对应的hbm文件

Student.hbm.xml

Classes.hbm.xml

<?xml version="1.0"?>
    <!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.yc.entity.Classes" table="CLASSES">
            <id name="cid" type="int">
                <column name="CID" />
                <generator class="sequence" >
                	<param name="sequence">seq_classes_cid</param>
                </generator>
            </id>
            <property name="cname" type="java.lang.String">
                <column name="CNAME" />
            </property>
            
            <set name="students" table="STUDENT" inverse="false" lazy="true">
            	
                <key>
                    <column name="CID" />
                </key>
                <one-to-many class="com.yc.entity.Student" />
            </set>
        </class>
    </hibernate-mapping>

3.在cfg文件中加入映射路径

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

4.编写测试类测试

package com.yc.test;
    
    import java.util.Collections;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.junit.Test;
    
    import com.yc.entity.Classes;
    import com.yc.entity.Student;
    import com.yc.utils.HibernateUtil;
    
    public class MyTest {
    
    	@Test
    	//插入数据的测试
    	public void testAdd() {
    		Classes c=new Classes("龙宫");
    
    		Student s1=new Student("龙太子");
    		Student s2=new Student("玄彩娥");
    
    		//如果希望在学生表中添加对应的班级编号，需要在班级中添加学生，建立关联关系
    		Collections.addAll(c.getStudents(), s1,s2);
    
    		Session session=HibernateUtil.getSession();
    		Transaction transaction=session.beginTransaction();
    
    		session.save(c);
    		session.save(s1);
    		session.save(s2);
    
    		transaction.commit();
    		HibernateUtil.closeSession(session);
    	}
    
    	@Test
    	//查询班级中包含的学生
    	public void testFind() {
    		Session session=HibernateUtil.getSession();
    		Classes c=(Classes) session.get(Classes.class, 1000);
    		//建立关联关系后，可以方便的从一个对象导航到另一个对象
    		System.out.println(c);
    	}
    
    	@Test
    	//修改学生信息
    	public void testUpdate() {
    		Classes c=new Classes("普陀山");
    
    		Session session=HibernateUtil.getSession();
    		Transaction transaction=session.beginTransaction();
    
    		Student s=(Student) session.get(Student.class, 1001);
    		c.getStudents().add(s);
    
    		session.save(c);
    
    		transaction.commit();
    		HibernateUtil.closeSession(session);
    	}
    
    	@Test
    	//删除
    	public void testDelete() {
    		Session session=HibernateUtil.getSession();
    		Transaction transaction=session.beginTransaction();
    
    		Student s=(Student) session.get(Student.class, 1000);
    		session.delete(s);
    
    		transaction.commit();
    		HibernateUtil.closeSession(session);
    	}
    }

5.测试结果，在这里我只贴出testAdd方法的测试结果，其余方法小伙伴门可以自己尝试

![20160813144437319][]

![20160813144452241][] ![20160813144501044][]

### 多对一的关联关系 ###

在这里其实我们只需改变实体类中的属性以及对应的hbm文件即可，其实多对一更加符合我们的数据库表的设计

1.实体类

package com.yc.entity;
    
    public class Student {
    	private int sid;
    	private String sname;
    	private Classes cid; //多对一
    	//在此就不贴出对应的set，get方法以及构造函数，toString方法
    }

package com.yc.entity;
    
    public class Classes {
    	private int cid;
    	private String cname;
    	//在此就不贴出对应的set，get方法以及构造函数，toString方法
    }

2.hbm文件

Student.hbm.xml

<?xml version="1.0"?>
    <!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.yc.entity.Student" table="STUDENT">
            <id name="sid" type="int">
                <column name="SID" />
                <generator class="sequence" >
                	<param name="sequence">seq_student_sId</param>
                </generator>
            </id>
            <property name="sname" type="java.lang.String">
                <column name="SNAME" />
            </property>
            <many-to-one name="cid" class="com.yc.entity.Classes" fetch="join">
                <column name="CID" />
            </many-to-one>
        </class>
    </hibernate-mapping>

Classes.hbm.xml

3.编写测试类运行

package com.yc.test;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.junit.Test;
    
    import com.yc.entity.Classes;
    import com.yc.entity.Student;
    import com.yc.utils.HibernateUtil;
    
    //测试多对一
    public class MyTest2 {
    
    	@Test
    	//测试多对一
    	public void testSave(){
    		Classes ct=new Classes();
    		ct.setCname("阴曹地府");
    
    		Student st1=new Student();
    		st1.setSname("杀破狼");
    
    		Student st2=new Student();
    		st2.setSname("骨精灵");
    
    		//设置关联关系
    		st1.setCid(ct);
    		st2.setCid(ct);
    
    		Session session=HibernateUtil.getSession();
    		Transaction tx=session.beginTransaction();
    
    		session.save(ct);
    		session.save(st1);
    		session.save(st2);
    
    		tx.commit();
    		HibernateUtil.closeSession(session);
    	}
    
    	@Test
    	//测试多对一
    	public void testFind(){
    		Session session=HibernateUtil.getSession();
    
    		Student s=(Student) session.get(Student.class,1002);
    		System.out.println(s);
    
    		HibernateUtil.closeSession(session);
    	}
    }

4.测试运行，同样在这里我只测试testSave方法

![20160813145957573][]

![20160813150015926][]           ![20160813150025917][]

### 双向的一对多 ###

其实双向的一对多就是将上述两种方法结合，以便于之后的操作

1.实体类

package com.yc.test3;
    
    import java.io.Serializable;
    
    public class Student3 implements Serializable{
    	private static final long serialVersionUID = 4829740592306007293L;
    
    	private int sid;
    	private String sname;
    	private Classes3 cid;
    	//在此同样省略相应的方法
    }

2.hbm文件

Student.hbm.xml

<?xml version="1.0"?>
    <!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.yc.entity.Student" table="STUDENT">
            <id name="sid" type="int">
                <column name="SID" />
                <generator class="sequence" >
                	<param name="sequence">seq_student_sId</param>
                </generator>
            </id>
            <property name="sname" type="java.lang.String">
                <column name="SNAME" />
            </property>
            <many-to-one name="cid" class="com.yc.entity.Classes" fetch="join">
                <column name="CID" />
            </many-to-one>
        </class>
    </hibernate-mapping>

Classes.hbm.xml

<?xml version="1.0"?>
    <!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.yc.entity.Classes" table="CLASSES">
            <id name="cid" type="int">
                <column name="CID" />
                <generator class="sequence" >
                	<param name="sequence">seq_classes_cid</param>
                </generator>
            </id>
            <property name="cname" type="java.lang.String">
                <column name="CNAME" />
            </property>
            <set name="students" table="STUDENT" inverse="false" lazy="true" >
            	
                <key>
                    <column name="CID" />
                </key>
                <one-to-many class="com.yc.entity.Student" />
            </set>
        </class>
    </hibernate-mapping>

3.测试类

package com.yc.test;
    
    import java.util.Collections;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.junit.Test;
    
    import com.yc.entity.Classes;
    import com.yc.entity.Student;
    import com.yc.utils.HibernateUtil;
    
    //测试双向一对多
    public class MyTest3 {
    	@Test
    	//测试多对一
    	public void testSave(){
    		Classes c=new Classes("大唐官府");
    
    		Student s1=new Student("剑侠客");
    		Student s2=new Student("飞燕女");
    
    		//设置关联关系
    		Collections.addAll(c.getStudents(), s1,s2);
    		s1.setCid(c);
    		s2.setCid(c);
    
    		Session session=HibernateUtil.getSession();
    		Transaction tx=session.beginTransaction();
    
    		session.save(c);
    		session.save(s1);
    		session.save(s2);
    
    		tx.commit();
    
    		HibernateUtil.closeSession(session);
    	}
    
    	@Test
    	public void testFind(){
    		Session session=HibernateUtil.getSession();
    
    		Classes c=(Classes) session.get(Classes.class, 1002);
    		Student s=(Student) session.get(Student.class, 1003);
    
    		System.out.println(c);
    		System.out.println(s);
    
    		HibernateUtil.closeSession(session);
    	}
    
    	@Test
    	//查询学生所在的班级的信息
    	public void testFingStudentClass(){
    		Session session=HibernateUtil.getSession();
    
    		Student s=(Student) session.get(Student.class, 1003);
    
    		System.out.println(s.getCid());
    
    		HibernateUtil.closeSession(session);
    	}
    }

4.测试运行，一样这里只测试testSave方法

![20160813151454000][]

![20160813151517172][] ![20160813151529011][]

写到这里我突然想起一件事情，HibernateUtil的代码忘记贴了，下面是我的代码

package com.yc.utils;
    
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.service.ServiceRegistry;
    import org.hibernate.service.ServiceRegistryBuilder;
    
    public class HibernateUtil {
    	private static SessionFactory sessionFactory;
    	private static Session session;
    
    	static{
    		// 创建配置对象
    		Configuration config = new Configuration().configure();
    		// 创建服务注册对象
    		ServiceRegistry serviceRegistry=new 
    				ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
    		// 创建会话工厂对象
    		sessionFactory = config.buildSessionFactory(serviceRegistry);
    	}
    
    	public static Session getSession(){
    		//创建会话对象
    		session = sessionFactory.openSession();
    
    		return session;
    	}
    
    	public static void closeSession(Session session){
    		if(session!=null){
    			//关闭会话
    			session.close();
    		}
    	}
    }

[20160813144437319]: /images/20220718/ecebc59f360c4b6b818782c045025923.png
[20160813144452241]: https://img-blog.csdn.net/20160813144452241
[20160813144501044]: /images/20220718/2f8bc7c4fedd4514949f4dcef2dfb195.png
[20160813145957573]: /images/20220718/27c0455c850e45ff91434e8e686fcf8e.png
[20160813150015926]: https://img-blog.csdn.net/20160813150015926
[20160813150025917]: /images/20220718/e59cca7785da4b8da592e5ce1ad4a724.png
[20160813151454000]: /images/20220718/e2fc6cb52c5c4e07894b8a9a72742e68.png
[20160813151517172]: https://img-blog.csdn.net/20160813151517172
[20160813151529011]: /images/20220718/6012f53828cd45e99fa921aee45e6053.png