MyBatis多表查询

基本准备创建项目，结构如下：

创建数据库

导入依赖


      junit
      junit
      4.11
      test
    
    
      org.mybatis
      mybatis
      3.4.6
    
    
      mysql
      mysql-connector-java
      5.1.45
    
    
      log4j
      log4j
      1.2.17
    
    
      org.mybatis
      mybatis
      3.4.6
      test

编写实体类

public class Order {
    private int id;
    private Date ordertime;  //下单时间
    private double total;   //总金额
    private User user;   //当前订单属于哪一个用户

    }

public class User {
    private int id;   //用户id
    private String username;   //用户名称
    private String password;   //用户密码
    private Date birthday;    //用户生日

    //当前用户存在那些订单
    private List orderList;

    //描述的是当前用户具备哪些角色
    private List roleList;
    }

public class Role {
    private int id;    //角色id
    private String roleName;   //角色名称
    private String roleDesc;   //角色描述
    }

1、一对一查询编写OrderMapper.xml文件（重点配置）

（1）方法一使用associate标签（匹配）





    
        
        
        
        
        
        
            
            
            
            
        
    

    
        SELECT *,o.id oid FROM orders o,user u WHERe o.uid=u.id

（2）方法二直接引用





    
        
        
        
        
        
        
        
        
       
    

    
        select * from user

3、多对多查询编写UserMapper.xml文件（可以写在一对多配置文件中重点配置）

4、测试代码如下：

package com.dhh.test;

import com.dhh.domain.Order;
import com.dhh.domain.User;
import com.dhh.mapper.OrderMapper;
import com.dhh.mapper.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class MyBatisTest {
    @Test    //多对多查询测试
    public void test3() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List userAndRoleAll= mapper.findUserAndRoleAll();
        for (User user:userAndRoleAll) {
            System.out.println(user);
        }

        sqlSession.close();
    }

    @Test   //一对多查询测试
    public void test2() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper=sqlSession.getMapper(UserMapper.class);
        List userList= mapper.findAll();
        for (User user:userList) {
            System.out.println(user);
        }

        sqlSession.close();
    }

    @Test    //一对一查询测试
    public void test1() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List orderList=mapper.findAll();
        for (Order order:orderList) {
            System.out.println(order);
        }
        sqlSession.close();
    }


}

5、小结

MyBatis多表配置方式：

一对一：使用做配置

一对多：使用+做配置

多对多：使用+做配置

总结：坚持很难，放弃容易，再接再厉，一起进步！

MyBatis多表查询

Java相关栏目本月热门文章