Hibernate注解（三）

关系映射级别注解

1.一对一单向外键

2.一对一双向外键关联

3.一对一双向外键联合主键

4.多对一单向外键关联

5.一对多单向外键关联

6.一对多双向外键关联

7.多对多单向外键关联

8.多对多双向外键关联

（一）一对一单向外键

@OneToOne(cascade=CascadeType.ALL)//cascade级联关系

@JoinColumn(name="pid",unique=true)//被控类的外键，写在主控类的表中，pid在主表中充当外键

注意：保存时因该先保存外键对象，再保存主表对象

主控方：含有外键的一方，被控方：被引用主键的一方。

例子：

被控方IdCard：

package com.relationannotation.entity.oto_pk;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

import org.hibernate.annotations.GenericGenerator;

/** 
 * 身份证类
 *
 * @author mrq
 */
@Entity
public class IdCard {
    
    @Id
    @GeneratedValue(generator="pid")
    @GenericGenerator(name="pid", strategy = "assigned")
    @Column(length=18)
    private String pid;//身份证号码
    
    private String sname;//学生姓名

    public IdCard(){
    }
    
    public IdCard(String pid, String sname) {
        this.pid = pid;
        this.sname = sname;
    }


    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }

    public String getSname() {
        return sname;
    }

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

主控方Students：

package com.relationannotation.entity.oto_pk;

import java.util.Date;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;

/** 
 * 学生实体类
 * 
 */
@Entity//(name = "t_students")
public class Students{
    
    
    private IdCard card;
    
    private int sid;//学号
    //@Id/* 联合主键，需要实现Serializable接口*/
    //@Column(length = 8)/* 列注解，length属性值字段的长度*/
    private String gender;//出生日期
    private Date birthday;//出生日期
    private String major;//专业
    
    public Students() {
    }

    public Students(IdCard card, String gender, Date birthday, String major) {
        this.card = card;
        this.gender = gender;
        this.birthday = birthday;
        this.major = major;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)//默认是自增长的
    public int getSid() {
        return sid;
    }

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


    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "pid",unique=true)//被控方的主键
    public IdCard getCard() {
        return card;
    }

    public void setCard(IdCard card) {
        this.card = card;
    }

    
    
    
    
    
    
    
}

配置文件hibernate.cfg.xml：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
    <session-factory>
       <property name="connection.username">root</property>
       <property name="connection.password">mysql</property>
       <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
       <property name="connection.url">jdbc:mysql:///hibernate?useUnicode=true&amp;characterEncoding=UTF-8</property>
       
       <!-- 配置数据的库的前缀 -->
       <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
           
           <!-- 
               是否把Hibernate运行时的SQL语句输出到控制台，编码阶段便于测试
            -->
           <property name="show_sql">true</property>
           <!-- 
               输出到控制台的SQL语句是否进行排版，便于阅读。建议设置true
            -->
           <property name="format_sql">true</property>
           <!-- 
               可以到帮助由java代码生成数据库脚本，进而生辰具体的表结构。
               create|update|create-drop|validate
            -->
           <property name="hbm2ddl.auto">create</property>
           
           <mapping class="com.relationannotation.entity.oto_pk.Students"/>
           <mapping class="com.relationannotation.entity.oto_pk.IdCard"/>
       <!--     <mapping class="com.entity.StudentA"/> -->
    </session-factory>
 
</hibernate-configuration>

测试用例：

package com.entity.oto_pk;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.Test;

import com.relationannotation.entity.oto_pk.IdCard;
import com.relationannotation.entity.oto_pk.Students;

public class TestStudent {

    /** 
    *  生成表格
    *  
    * @param     
    * @return void    
    * @throws 
    */
    @Test
    public void testeSchemaExport() {

        // 创建hibernate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();
        // 生成sessionFactory
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        SchemaExport export = new SchemaExport(config);
        export.create(true, true);
    }
    
    /** 
    * 增加一个学生
    *  
    * @param     
    * @return void    
    * @throws 
    */
    @Test
    public void testAddStudent() {

        // 创建hibernate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();
        // 生成sessionFactory
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        
        Session session = sessionFactory.openSession();
        
        Transaction tx = session.beginTransaction();
        
        IdCard card = new IdCard("323232323232323232","张三");
        Students students = new Students(card, "男", new Date(), "数学");

        session.save(card);//先保存身份证
        session.save(students);//后保存学生
        
        tx.commit();
        session.close();
        
        
    }
    

}

 （二）一对一双向外键

主控方的配置通一对一单向外键关联

@OneToOne(mappedBy="card")//被控方 mappedBy表示把控制权交给主控方

双向关联，被空方必须设置mappedBy属性。因为双向关联只能交给一方去控制，不肯能在双方都设置外键保存关联关系，否则双方都无法保存。

例子：

被控方IdCard：

package com.relationannotation.entity.oto_bfk;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;

import org.hibernate.annotations.GenericGenerator;

/** 
 * 身份证类
 *
 * @author mrq
 */
@Entity
public class IdCard {
    
    @Id
    @GeneratedValue(generator="pid")
    @GenericGenerator(name="pid", strategy = "assigned")
    @Column(length=18)
    private String pid;//身份证号码
    
    private String sname;//学生姓名

    @OneToOne(mappedBy="card")//这里把控制权交给主控方
    private Students stu;
    
    public IdCard(){
    }
    
    public IdCard(String pid, String sname) {
        this.pid = pid;
        this.sname = sname;
    }


    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }

    public String getSname() {
        return sname;
    }

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

    public Students getStu() {
        return stu;
    }

    public void setStu(Students stu) {
        this.stu = stu;
    }
    
    
    
    
    
}

主控方Students：

package com.relationannotation.entity.oto_bfk;

import java.util.Date;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;

/** 
 * 学生实体类
 * 
 */
@Entity//(name = "t_students")
public class Students{
    
    
    private IdCard card;
    
    private int sid;//学号
    //@Id/* 联合主键，需要实现Serializable接口*/
    //@Column(length = 8)/* 列注解，length属性值字段的长度*/
    private String gender;//出生日期
    private Date birthday;//出生日期
    private String major;//专业
    
    public Students() {
    }

    public Students(IdCard card, String gender, Date birthday, String major) {
        this.card = card;
        this.gender = gender;
        this.birthday = birthday;
        this.major = major;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)//默认是自增长的
    public int getSid() {
        return sid;
    }

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


    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "pid",unique=true)//被控方的主键
    public IdCard getCard() {
        return card;
    }

    public void setCard(IdCard card) {
        this.card = card;
    }

    
    
    
    
    
    
    
}

配置文件hibernate.cfg.xml：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
    <session-factory>
       <property name="connection.username">root</property>
       <property name="connection.password">mysql</property>
       <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
       <property name="connection.url">jdbc:mysql:///hibernate?useUnicode=true&amp;characterEncoding=UTF-8</property>
       
       <!-- 配置数据的库的前缀 -->
       <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
           
           <!-- 
               是否把Hibernate运行时的SQL语句输出到控制台，编码阶段便于测试
            -->
           <property name="show_sql">true</property>
           <!-- 
               输出到控制台的SQL语句是否进行排版，便于阅读。建议设置true
            -->
           <property name="format_sql">true</property>
           <!-- 
               可以到帮助由java代码生成数据库脚本，进而生辰具体的表结构。
               create|update|create-drop|validate
            -->
           <property name="hbm2ddl.auto">create</property>
           
           <mapping class="com.relationannotation.entity.oto_bfk.Students"/>
           <mapping class="com.relationannotation.entity.oto_bfk.IdCard"/>
       <!--     <mapping class="com.entity.StudentA"/> -->
    </session-factory>
 
</hibernate-configuration>

测试用例和上述一样的结果。

（三）一对一双向外键联合主键

创建主键类

主键类必须实现Serializable接口，重写hashCode()和equals()方法。

主键类

@Embeddable

实体类

@EmbeddedId

（四）多对一单向外键

多方持有一方的引用，比如：多个学生对应一个班级（多对一）

@ManyToOne（cascade={CascadeType.ALL},fetch=FetchType.EAGER）

@JoinColumn（name="cid",referencedColumnName=""CID）//name一方的外键，referencedColumnName表示映射到数据库的列名，

例子：

一方ClassRoom：

package com.relationannotation.entity.mto_fk;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

import org.hibernate.annotations.GenericGenerator;

/*班级实体类*/
@Entity
public class ClassRoom {
    
    @Id
    @GeneratedValue(generator="cid")
    @GenericGenerator(name="cid",strategy="assigned")
    @Column(length=4)
    private String cid;//班级的编号
    
    private String cname;//班级的名字
    
    public ClassRoom(){
    }
    
    
    
    public ClassRoom(String cid, String cname) {
        this.cid = cid;
        this.cname = cname;
    }



    public String getCid() {
        return cid;
    }

    public void setCid(String cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }
    
    
}

多方StudentM：

package com.relationannotation.entity.mto_fk;

import java.util.Date;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;

/*学生实体类*/
@Entity
public class StudentM {
    
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)//默认是自增长的
    private int sid;//学号
    
    private String sname;
    
    private String gender;//性别
    
    private Date birthday;//出生日期
    
    private String major;//专业
    
    @ManyToOne(cascade={CascadeType.ALL},fetch=FetchType.EAGER)
    @JoinColumn(name="cidcid",referencedColumnName="cid")//name是外键的列名，referencedColumnName引用外键的表的主键
    private ClassRoom classRoom;//
    
    public StudentM() {
    }


    public StudentM(String sname, String gender, Date birthday, String major) {
        this.sname = sname;
        this.gender = gender;
        this.birthday = birthday;
        this.major = major;
    }


    public int getSid() {
        return sid;
    }

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

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    public ClassRoom getClassRoom() {
        return classRoom;
    }

    public void setClassRoom(ClassRoom classRoom) {
        this.classRoom = classRoom;
    }


    public String getSname() {
        return sname;
    }


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

    
    
    
    
}

配置文件相应的mapping修改一下

测试用例：

package com.entity.mto_fk;


import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.Test;

import com.relationannotation.entity.mto_fk.ClassRoom;
import com.relationannotation.entity.mto_fk.StudentM;


public class TestStudent {

    /** 
    *  生成表格
    *  
    * @param     
    * @return void    
    * @throws 
    */
    @Test
    public void testeSchemaExport() {

        // 创建hibernate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();
        // 生成sessionFactory
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        SchemaExport export = new SchemaExport(config);
        export.create(true, true);
    }
    
    @Test
    public void addStudents(){
        Configuration config = new Configuration().configure();
        // 创建服务注册对象
        ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties())
                .buildServiceRegistry();
        // 生成sessionFactory
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        Session session = sessionFactory.openSession();
        Transaction tx = session.beginTransaction();
        
        //先创建班级对象
        ClassRoom c1 = new ClassRoom("C001","软件工程");
        ClassRoom c2 = new ClassRoom("C002","网络工程");
        
        //创建是个学生
        StudentM s1 = new StudentM("张三","男", new Date(), "计算机");
        StudentM s2 = new StudentM("李四","男", new Date(), "计算机");
        StudentM s3 = new StudentM("王五","女", new Date(), "计算机");
        StudentM s4 = new StudentM("赵六","女", new Date(), "计算机");
        
        s1.setClassRoom(c1);
        s2.setClassRoom(c1);
        
        s3.setClassRoom(c2);
        s4.setClassRoom(c2);
        
        //先保存班级
        session.save(c1);
        session.save(c2);
        session.save(s1);
        session.save(s2);
        session.save(s3);
        session.save(s4);
        
        
        tx.commit();
        session.close();
    }
    
    
}

（五）一对多单向外键

一方持有多方的集合，一个班级有多个学生（一对多）。

@OneToMany(cascade={CascadeType.ALL},fetch=FetchType.LAZY)

@JoinColumn(name="cid")例子：

一方ClassRoom：

package com.relationannotation.entity.otm_fk;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;

import org.hibernate.annotations.GenericGenerator;

/*班级实体类*/
@Entity
public class ClassRoom {
    
    @Id
    @GeneratedValue(generator="cid")
    @GenericGenerator(name="cid",strategy="assigned")
    @Column(length=4)
    private String cid;//班级的编号
    
    private String cname;//班级的名字
    
    @OneToMany(cascade={CascadeType.ALL},fetch=FetchType.LAZY)
    @JoinColumn(name="cid")
    private Set<StudentM> stus;
    
    public ClassRoom(){
    }
    
    
    
    public ClassRoom(String cid, String cname) {
        this.cid = cid;
        this.cname = cname;
    }



    public String getCid() {
        return cid;
    }

    public void setCid(String cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public Set<StudentM> getStus() {
        return stus;
    }

    public void setStus(Set<StudentM> stus) {
        this.stus = stus;
    }
    
    
    
}

多方StudentM：

package com.relationannotation.entity.otm_fk;

import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

/*学生实体类*/
@Entity
public class StudentM {
    
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)//默认是自增长的
    private int sid;//学号
    
    private String sname;
    
    private String gender;//性别
    
    private Date birthday;//出生日期
    
    private String major;//专业
    
    public StudentM() {
    }


    public StudentM(String sname, String gender, Date birthday, String major) {
        this.sname = sname;
        this.gender = gender;
        this.birthday = birthday;
        this.major = major;
    }


    public int getSid() {
        return sid;
    }

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

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }


    public String getSname() {
        return sname;
    }


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

    
    
    
    
}

 晕倒！@注解，要么都写在属性上，要么都写到getter方法上，否则会出错org.hibernate.MappingException: Could not determine type for；

（六）多对多单向外键

学生和教师构成多对多的关联关系

其中一个多方持有另一个多方的集合对象（学生持有教师的集合）

创建中间表

@ManyToMany

@JoinTable(name="teachers_students",joinColumns={@JoinColumn(name="sid")},inverseJoinColumns={@JoinColumn(name="tid")})

例子：

学生类StudentM：

package com.relationannotation.entity.mtm_fk;

import java.util.Date;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;

/*学生实体类*/
@Entity
public class StudentM {

    
    private int sid;// 学号

    private String sname;

    private String gender;// 性别

    private Date birthday;// 出生日期

    private String major;// 专业

    
    private Set<Teachers> teachers;//

    public StudentM() {
    }

    public StudentM(String sname, String gender, Date birthday, String major) {
        this.sname = sname;
        this.gender = gender;
        this.birthday = birthday;
        this.major = major;
    }
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO) // 默认是自增长的
    public int getSid() {
        return sid;
    }

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

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }
    
    @ManyToMany
    @JoinTable(name = "teachers_students", joinColumns = { @JoinColumn(name = "sid") }, inverseJoinColumns = {
            @JoinColumn(name = "tid") })
    public Set<Teachers> getTeachers() {
        return teachers;
    }

    public void setTeachers(Set<Teachers> teachers) {
        this.teachers = teachers;
    }

}

教师类Teachers：

package com.relationannotation.entity.mtm_fk;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

import org.hibernate.annotations.GenericGenerator;

/*教师实体类*/
@Entity
public class Teachers {
    
    
    private String tid;//教师的编号
    
    private String tname;//教师的姓名

    public Teachers() {
    }

    public Teachers(String tid, String tname) {
        this.tid = tid;
        this.tname = tname;
    }
    
    @Id
    @GeneratedValue(generator="tid")
    @GenericGenerator(name="tid",strategy="assigned")
    @Column(length=4)
    public String getTid() {
        return tid;
    }

    public void setTid(String tid) {
        this.tid = tid;
    }

    public String getTname() {
        return tname;
    }

    public void setTname(String tname) {
        this.tname = tname;
    }
    
    
    
    
    
    
}

配置文件中mapping映射上述两个类

测试文件

package com.entity.mtm_fk;


import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.Test;


public class TestStudent {

    /** 
    *  生成表格
    *  
    * @param     
    * @return void    
    * @throws 
    */
    @Test
    public void testeSchemaExport() {

        // 创建hibernate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();
        // 生成sessionFactory
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        SchemaExport export = new SchemaExport(config);
        export.create(true, true);
    }
    
    @Test
    public void addStudents(){
    }
    
    
}

（七）多对多单向外键

就是Teachers类中持有学生的引用，加上@ManyToMany(mappedBy="teachers")

package com.relationannotation.entity.mtm_fk;

import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

import org.hibernate.annotations.GenericGenerator;

/*教师实体类*/
@Entity
public class Teachers {
    
    
    private String tid;//教师的编号
    
    private String tname;//教师的姓名
    
    private Set<StudentM> studentM;//

    public Teachers() {
    }

    public Teachers(String tid, String tname) {
        this.tid = tid;
        this.tname = tname;
    }
    
    @Id
    @GeneratedValue(generator="tid")
    @GenericGenerator(name="tid",strategy="assigned")
    @Column(length=4)
    public String getTid() {
        return tid;
    }

    public void setTid(String tid) {
        this.tid = tid;
    }

    public String getTname() {
        return tname;
    }

    public void setTname(String tname) {
        this.tname = tname;
    }
    @ManyToMany(mappedBy="teachers")
    public Set<StudentM> getStudentM() {
        return studentM;
    }

    public void setStudentM(Set<StudentM> studentM) {
        this.studentM = studentM;
    }

    
    
    
}