多对多关系数据库表 java描述

多对多关系 需要建立一张新表存放它们的对应数据

sql语句

 create table teacher(
     id int primary key,
     name varchar(100),
     money float(8,2)
 );
 create table student(
     id int primary key,
     name varchar(100),
     grade varchar(10)
 );
 create table teacher_student(
     t_id int,
     s_id int,
     primary key(t_id,s_id),
     constraint t_id_fk foreign key(t_id) references teacher(id),
     constraint s_id_fk foreign key(s_id) references student(id)
 );

domain

Teacher.java

 package cn.itcast.domain;

 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
 /**
 create table teacher(
     id int primary key,
     name varchar(100),
     money float(8,2)
 );
 create table student(
     id int primary key,
     name varchar(100),
     grade varchar(10)
 );
 create table teacher_student(
     t_id int,
     s_id int,
     primary key(t_id,s_id),
     constraint t_id_fk foreign key(t_id) references teacher(id),
     constraint s_id_fk foreign key(s_id) references student(id)
 );
  * @author wzhting
  *
  */
 public class Teacher implements Serializable {
     private Integer id;
     private String name;
     private float money;
     private List<Student> stus = new ArrayList<Student>();
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public float getMoney() {
         return money;
     }
     public void setMoney(float money) {
         this.money = money;
     }
     public List<Student> getStus() {
         return stus;
     }
     public void setStus(List<Student> stus) {
         this.stus = stus;
     }

 }

Student.java

 package cn.itcast.domain;

 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;

 public class Student implements Serializable {
     private Integer id;
     private String name;
     private String grade;
     private List<Teacher> ts = new ArrayList<Teacher>();
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public String getGrade() {
         return grade;
     }
     public void setGrade(String grade) {
         this.grade = grade;
     }
     public List<Teacher> getTs() {
         return ts;
     }
     public void setTs(List<Teacher> ts) {
         this.ts = ts;
     }

 }

daoImpl.java

 package cn.itcast.dao.impl;

 import java.sql.SQLException;
 import java.util.List;

 import org.apache.commons.dbutils.QueryRunner;
 import org.apache.commons.dbutils.handlers.BeanHandler;
 import org.apache.commons.dbutils.handlers.BeanListHandler;
 import org.apache.commons.dbutils.handlers.ScalarHandler;

 import cn.itcast.domain.Student;
 import cn.itcast.domain.Teacher;
 import cn.itcast.util.DBCPUtil;

 public class TeacherDaoImpl {
     private QueryRunner qr = new QueryRunner(DBCPUtil.getDataSource());
     public void addTeacher(Teacher t) throws SQLException{
         //保存老师的基本信息
         qr.update("insert into teacher(id,name,money) values(?,?,?)", t.getId(),t.getName(),t.getMoney());
         //判断t中是否有学生
         List<Student> stus = t.getStus();
         //有学生：判断该学生是否在student表中；在，不添加了；不在，添加进去
         if(stus!=null&&stus.size()>0){
             for(Student s:stus){
                 Object num =  qr.query("select 1 from student where id=?", new ScalarHandler(1), s.getId());//判断学生是否已在数据库中
                 if(num==null){
                     //学生信息不存在
                     qr.update("insert into student (id,name,grade) values(?,?,?)", s.getId(),s.getName(),s.getGrade());
                 }
                 //在第三方表中建立老师和学生的关系
                 qr.update("insert into teacher_student (t_id,s_id) values(?,?)", t.getId(),s.getId());
             }
         }

     }

     public Teacher findTeacher(Integer id) throws SQLException{
         //查询老师的基本信息
         Teacher t = qr.query("select * from teacher where id=?", new BeanHandler<Teacher>(Teacher.class), id);
         if(t!=null){
         //根据老师的id查学生的基本信息：方式三种
 //            String sql = "select * from student where id in (select s_id from teacher_student where t_id=?)";//子查询
 //            String sql = "select s.* from student s,teacher_student ts where s.id=ts.s_id and ts.t_id=?";//隐式内连接
             String sql = "select s.* from student s inner join teacher_student ts on s.id=ts.s_id where ts.t_id=?";;//显式内连接
             List<Student> stus = qr.query(sql, new BeanListHandler<Student>(Student.class), id);
             t.setStus(stus);
         }
         return t;
     }
 }

test

测试

 package cn.itcast.test;

 import java.sql.SQLException;
 import java.util.List;

 import org.junit.Test;

 import cn.itcast.dao.impl.TeacherDaoImpl;
 import cn.itcast.domain.Student;
 import cn.itcast.domain.Teacher;

 public class TeacherDaoImplTest {
     private TeacherDaoImpl dao = new TeacherDaoImpl();
     @Test
     public void testAddTeacher() throws SQLException {
         Teacher t1 = new Teacher();
         t1.setId(1);
         t1.setName("bxd");
         t1.setMoney(20000);

         Teacher t2 = new Teacher();
         t2.setId(2);
         t2.setName("wzt");
         t2.setMoney(15000);

         Student s1 = new Student();
         s1.setId(1);
         s1.setName("gfy");
         s1.setGrade("A");

         Student s2 = new Student();
         s2.setId(2);
         s2.setName("wxy");
         s2.setGrade("A");

         t1.getStus().add(s1);
         t1.getStus().add(s2);

         t2.getStus().add(s1);
         t2.getStus().add(s2);

         dao.addTeacher(t1);
         dao.addTeacher(t2);

     }

     @Test
     public void testFindTeacher() throws SQLException {
         Teacher t = dao.findTeacher(2);
         System.out.println(t.getName());
         List<Student> stus = t.getStus();
         for(Student s:stus)
             System.out.println(s.getName());
     }

 }