Hibernate中的单向多对一关联

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继上回讲到 Hibernate中的单向一对多关联，这次来实现一下Hibernate中的单向多对一关联。对原来的项目修改如下：

Hibernate中的单向多对一关联，需要我们在多方增加一个一方的属性，并且在多方的映射配置文件中添加many-to-one的配置。

Grade.java

package com.imooc.entity;import java.io.Serializable;import java.util.HashSet;import java.util.Set;/** * Created by DreamBoy on 2016/5/18. */public class Grade implements Serializable {    private int gid;    private String gname;    private String gdesc;    public Grade() {    }    public Grade(int gid, String gname, String gdesc, Set<Student> students) {        this.gid = gid;        this.gname = gname;        this.gdesc = gdesc;    }    public Grade(String gname, String gdesc) {        this.gname = gname;        this.gdesc = gdesc;    }    public int getGid() {        return gid;    }    public void setGid(int gid) {        this.gid = gid;    }    public String getGname() {        return gname;    }    public void setGname(String gname) {        this.gname = gname;    }    public String getGdesc() {        return gdesc;    }    public void setGdesc(String gdesc) {        this.gdesc = gdesc;    }}

Grade.hbm.xml

<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.imooc.entity.Grade" table="grade">        <id name="gid" column="gid" type="java.lang.Integer">            <generator class="increment"/>        </id>        <property name="gname" type="java.lang.String">            <column name="gname" length="20" not-null="true"/>        </property>        <property name="gdesc">            <column name="gdesc"/>        </property>    </class></hibernate-mapping>

Student.java

package com.imooc.entity;import java.io.Serializable;/** * Created by DreamBoy on 2016/5/18. */public class Student implements Serializable {    private int sid;    private String sname;    private String sex;    //在多方定义一个一方的引用    private Grade grade;    public Student() {    }    public Student(String sname, String sex) {        this.sname = sname;        this.sex = sex;    }    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 getSex() {        return sex;    }    public void setSex(String sex) {        this.sex = sex;    }    public Grade getGrade() {        return grade;    }    public void setGrade(Grade grade) {        this.grade = grade;    }}

Student.hbm.xml

<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.imooc.entity.Student" table="student">        <id name="sid" column="sid" type="java.lang.Integer">            <generator class="increment"/>        </id>        <property name="sname" type="java.lang.String">            <column name="sname" length="20" not-null="true"/>        </property>        <property name="sex">            <column name="sex"/>        </property>        <!-- 配置多对一关联关系 -->        <many-to-one name="grade" class="com.imooc.entity.Grade" column="gid"></many-to-one>    </class></hibernate-mapping>

重要的配置为：

<!-- 配置多对一关联关系 -->        <many-to-one name="grade" class="com.imooc.entity.Grade" column="gid"></many-to-one>

Test.java

package com.imooc.test;/** * Created by DreamBoy on 2016/5/18. */import com.imooc.entity.Grade;import com.imooc.entity.Student;import com.imooc.util.HibernateUtil;import org.hibernate.Session;import org.hibernate.Transaction;import java.util.Set;/** * 单向多对一（学生---》班级） */public class Test {    public static void main(String[] args) {        save();    }    //保存    public static void save() {        Grade g = new Grade("Java一班", "Java软件开发一班");        Student stu1 = new Student("哈", "女");        Student stu2 = new Student("哇", "男");        //设置关联关系，指定多到一的关联关系        stu1.setGrade(g);        stu2.setGrade(g);        Session session = HibernateUtil.getSession();        Transaction tx = session.beginTransaction();        session.save(g);        session.save(stu1);        session.save(stu2);        tx.commit();        HibernateUtil.closeSession(session);    }}

注意：在执行Test类前，需要删除掉上次项目中数据库中表的数据。HibernateUtil类与上回项目中的一致，Hibernate的配置文件也一致。

总结：

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