SSM15.1【Mybatis：Mybatis的多表操作之一对一】

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

package com.haifei.domain;

import java.util.Date;
import java.util.List;

/**
 * user表
 */
public class User {

    private int id;
    private String username;
    private String password;
    private Date birthday;


    public Date getBirthday() {
        return birthday;
    }

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    //1:1
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

 

 

package com.haifei.domain;

import java.util.Date;

/**
 * orders表
 * 因为order是mysql数据库的关键字，所以建表时命名为orders
 */
public class Order {

    private int id; //orders主键
    private Date ordertime; //orders表中该字段数据类型设置为datatime
    private double total;
//    private int uid; //orders外键；但从面向对象思想上讲，在java中实现外键时实际应用中多采用相关对象的方式


    //当前订单属于哪一个用户
    private User user;
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Date getOrdertime() {
        return ordertime;
    }

    public void setOrdertime(Date ordertime) {
        this.ordertime = ordertime;
    }

    public double getTotal() {
        return total;
    }

    public void setTotal(double total) {
        this.total = total;
    }


    @Override
    public String toString() {
        return "Order{" +
                "id=" + id +
                ", ordertime=" + ordertime +
                ", total=" + total +
                ", user=" + user +
                '}';
    }
}

package com.haifei.mapper;

import com.haifei.domain.Order;

import java.util.List;

public interface OrderMapper {

    public List<Order> findAll();

}

 

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.haifei.mapper.OrderMapper">
    <resultMap id="orderMap" type="order">
        <!--手动指定 [sql语句执行结果的]数据库表的字段（column）与java实体类的属性（property） 的映射关系-->
        <id column="oid" property="id" />
        <result column="ordertime" property="ordertime"/>
        <result column="total" property="total"/>

        <!--<result column="uid" property="user.id"/>
            <result column="username" property="user.username"/>
            <result column="password" property="user.password"/>
            <result column="birthday" property="user.birthday"/>-->
        <!--还可以这样设置-->
        <association property="user" javaType="user">
            <!--
                property: 当前实体(order)中的属性名称(private User user)
                javaType: 当前实体(order)中的属性的类型(User)
            -->
            <result column="uid" property="id"/>
            <result column="username" property="username"/>
            <result column="password" property="password"/>
            <result column="birthday" property="birthday"/>
        </association>
    </resultMap>
    
    <select id="findAll" resultMap="orderMap">
         SELECT *,o.id oid FROM orders o,user u WHERE o.uid=u.id
    </select>
</mapper>

/**
     * 一对一查询
     *  场景：一个订单属于一个用户
     * @throws IOException
     */
    @Test
    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<Order> orderList = mapper.findAll();
        for (Order order : orderList) {
            System.out.println(order);
        }
        /*
        Order{id=1, ordertime=Thu Jan 01 08:00:02 CST 1970, total=3000.0, user=User{id=1, username='zhangsan', password='123', birthday=Sat Jul 24 20:00:29 CST 2021}}
        Order{id=2, ordertime=Thu Jan 01 08:00:02 CST 1970, total=1000.0, user=User{id=2, username='lisi', password='345', birthday=Sat Jul 24 20:00:29 CST 2021}}
        Order{id=3, ordertime=Thu Jan 01 08:00:02 CST 1970, total=344.0, user=User{id=1, username='zhangsan', password='123', birthday=Sat Jul 24 20:00:29 CST 2021}}
        Order{id=4, ordertime=Thu Jan 01 08:00:02 CST 1970, total=455.0, user=User{id=2, username='lisi', password='345', birthday=Sat Jul 24 20:00:29 CST 2021}}
        Order{id=5, ordertime=Thu Jan 01 08:00:02 CST 1970, total=100.0, user=User{id=3, username='tom', password='abc', birthday=Sat Jul 24 20:00:29 CST 2021}}
         */

        sqlSession.close();
    }