4.1准备数据表和简单数据

CREATE TABLE orders(
   order_id INT PRIMARY KEY AUTO_INCREMENT,
   order_no VARCHAR(20),
   order_price FLOAT
);INSERT INTO orders(order_no, order_price) VALUES('aaaa', 23);
INSERT INTO orders(order_no, order_price) VALUES('bbbb', 33);
INSERT INTO orders(order_no, order_price) VALUES('cccc', 22);

4.2定义实体类

Orders.java

package com.entity;

public class Orders {
    private int id;
    private String name;
    private int price;
    public Orders()
    {
        
    }
    public Orders(int id, String name, int price) {
        super();
        this.id = id;
        this.name = name;
        this.price = price;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Orders [id=" + id + ", name=" + name + ", price=" + price + "]";
    }
}

4.3解决字段名和实体类属性名的两种不同配置方式

orderMapper.xml

<?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.config.ordersMapper">

    <!-- 方式一: 通过在 sql 语句中定义别名 <select id="selectOrder" parameterType="int" resultType="com.entity.Orders"> 
        select order_id id, order_no name,order_price price from orders where order_id=#{id} 
        </select> -->

    <!-- 方式二: 通过<resultMap> -->
    <select id="selectOrderResultMap" parameterType="int" resultMap="orderResultMap">
        select * from orders where order_id=#{id}
    </select>

    <resultMap id="orderResultMap" type="com.entity.Orders">
        <id property="id" column="order_id" />
        <result property="name" column="order_no" />
        <result property="price" column="order_price" />
    </resultMap>
</mapper>

4.4测试方法

Test3.java

package com.test;

import java.io.IOException;
import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;



import com.entity.Orders;
import com.inter.UserMapper;
import com.util.MybatisUtil;

public class Test3 {
        //测试查询
        @Test
        public void testGetOrders() throws IOException
        {
            SqlSession session=MybatisUtil.getSession();
            String statement="com.config.ordersMapper.selectOrderResultMap";
            Orders orders=session.selectOne(statement, 1);
            session.close();
            System.out.println(orders);
        }

}