package com.qcf.pox;

 import java.util.HashSet;

 import java.util.Set;

 import javax.persistence.CascadeType;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.OneToMany;

 import javax.persistence.Table;

 import org.hibernate.annotations.Cascade;

 import org.hibernate.annotations.Formula;

 //实体类

 @Entity

 @Table(name="_class")

 public class ClassName {

     @Id

     @GeneratedValue(strategy=GenerationType.AUTO)//设置id生成方式

     private int classid;

     @Column(name="classname")

     private String name;

     /*

      * 用一个查询语句动态的生成一个类的属性. 表示这个属性是一个虚拟的列，表中并没有这个列。需要通过查询语句计算出来。

      */

     //@Formula("(select count(*) from student s where s.className_classid=classid)")

     private int num;

     /*

      * mappedBy指定谁来维护关系，mappedBy在一方表示由多方来维护关系，在进行操作时要注意不要使用这一方来save,update等操作

      */

     @OneToMany(mappedBy="classname",cascade=CascadeType.ALL)

     private Set<Student> students=new HashSet<Student>();

     public ClassName(int classid, String name, int num, Set<Student> students) {

         super();

         this.classid = classid;

         this.name = name;

         this.num = num;

         this.students = students;

     }

     public Set<Student> getStudents() {

         return students;

     }

     public void setStudents(Set<Student> students) {

         this.students = students;

     }

     public int getClassid() {

         return classid;

     }

     public void setClassid(int classid) {

         this.classid = classid;

     }

     public String getName() {

         return name;

     }

     public void setName(String name) {

         this.name = name;

     }

     public int getNum() {

         return num;

     }

     public void setNum(int num) {

         this.num = num;

     }

     public ClassName(int classid, String name, int num) {

         super();

         this.classid = classid;

         this.name = name;

         this.num = num;

     }

     public ClassName() {

         super();

     }

 }

 package com.qcf.pox;

 import java.util.Date;

 import javax.persistence.Entity;

 import javax.persistence.FetchType;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.ManyToOne;

 @Entity

 public class Student {

     @Id

     @GeneratedValue(strategy=GenerationType.AUTO)//代表主键的生成策略

     private int stuno;

     private String stuname;

     private Date birthday;

     @ManyToOne

     private ClassName classname;

     public int getStuno() {

         return stuno;

     }

     public ClassName getClassName() {

         return classname;

     }

     public void setClassName(ClassName className) {

         this.classname = className;

     }

     public void setStuno(int stuno) {

         this.stuno = stuno;

     }

     public String getStuname() {

         return stuname;

     }

     public void setStuname(String stuname) {

         this.stuname = stuname;

     }

     public Date getBirthday() {

         return birthday;

     }

     public void setBirthday(Date birthday) {

         this.birthday = birthday;

     }

     public Student() {

         super();

     }

     public Student(int stuno, String stuname, Date birthday) {

         super();

         this.stuno = stuno;

         this.stuname = stuname;

         this.birthday = birthday;

     }

 }

         <!-- 引入映射文件 -->

         <mapping class="com.qcf.pox.Student"/>

         <mapping class="com.qcf.pox.ClassName"/>

 package com.qcf.test;

 import java.util.Date;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.Transaction;

 import org.hibernate.cfg.AnnotationConfiguration;

 import org.hibernate.cfg.Configuration;

 import com.qcf.pox.ClassName;

 import com.qcf.pox.Student;

 public class TestManyToOne {

     public static void main(String[] args) {

         //获取hibernate配置文件并取得session对象

         Configuration configuration=new AnnotationConfiguration().configure();

         SessionFactory factory=configuration.buildSessionFactory();

         Session session=factory.openSession();

         //开启事务

         Transaction transaction=session.beginTransaction();

         //创建classname实例

         ClassName className=new ClassName();

         className.setName("java");

         //创建student实例

         Student student=new Student();

         student.setStuname("zhangsan");

         student.setBirthday(new Date());

         student.setClassName(className);

         session.save(className);

         session.save(student);

         //提交事务

         transaction.commit();

         //关闭session

         session.close();

     }

 }