MyBatis学习教程(四)-如何快速解决字段名与实体类属性名不相同的冲突问题

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); 

package me.gacl.domain;
/**
* @author gacl
* 定义orders表对应的实体类
*/
public class Order {
/**
* 
CREATE TABLE orders(
order_id INT PRIMARY KEY AUTO_INCREMENT,
order_no VARCHAR(), 
order_price FLOAT
);
*/
//Order实体类中属性名和orders表中的字段名是不一样的
private int id; //id===>order_id
private String orderNo; //orderNo===>order_no
private float price; //price===>order_price
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getOrderNo() {
return orderNo;
}
public void setOrderNo(String orderNo) {
this.orderNo = orderNo;
}
public float getPrice() {
return price;
}
public void setPrice(float price) {
this.price = price;
}
@Override
public String toString() {
return "Order [id=" + id + ", orderNo=" + orderNo + ", price=" + price+ "]";
}
} 

<?xml version="." encoding="UTF-" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper .//EN" "http://mybatis.org/dtd/mybatis--mapper.dtd">
<!-- 为这个mapper指定一个唯一的namespace，namespace的值习惯上设置成包名+sql映射文件名，这样就能够保证namespace的值是唯一的
例如namespace="me.gacl.mapping.orderMapper"就是me.gacl.mapping(包名)+orderMapper(orderMapper.xml文件去除后缀)
-->
<mapper namespace="me.gacl.mapping.orderMapper">
<!-- 

-->
<select id="getOrderById" parameterType="int" 
resultType="me.gacl.domain.Order">
select * from orders where order_id=#{id}
</select>
<!-- 

-->
<select id="selectOrder" parameterType="int" 
resultType="me.gacl.domain.Order">
select order_id id, order_no orderNo,order_price price from orders where order_id=#{id}
</select>
<!-- 

<select id="selectOrderResultMap" parameterType="int" resultMap="orderResultMap">
select * from orders where order_id=#{id}
</select>
<!--通过<resultMap>映射实体类属性名和表的字段名对应关系 -->
<resultMap type="me.gacl.domain.Order" id="orderResultMap">
<!-- 用id属性来映射主键字段 -->
<id property="id" column="order_id"/>
<!-- 用result属性来映射非主键字段 -->
<result property="orderNo" column="order_no"/>
<result property="price" column="order_price"/>
</resultMap>
</mapper> 

<mappers> 
<!-- 注册orderMapper.xml文件， 
orderMapper.xml位于me.gacl.mapping这个包下，所以resource写成me/gacl/mapping/orderMapper.xml-->
<mapper resource="me/gacl/mapping/orderMapper.xml"/>
</mappers>

package me.gacl.test;
import me.gacl.domain.Order;
import me.gacl.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
public class Test {
@Test
public void testGetOrderById(){
SqlSession sqlSession = MyBatisUtil.getSqlSession();
/**
* 映射sql的标识字符串，
* me.gacl.mapping.orderMapper是orderMapper.xml文件中mapper标签的namespace属性的值，
* getOrderById是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
*/
String statement = "me.gacl.mapping.orderMapper.getOrderById";//映射sql的标识字符串
//执行查询操作，将查询结果自动封装成Order对象返回
Order order = sqlSession.selectOne(statement,);//查询orders表中id为的记录
//使用SqlSession执行完SQL之后需要关闭SqlSession
sqlSession.close();
System.out.println(order);//打印结果：null，也就是没有查询出相应的记录
}
@Test
public void testGetOrderById(){
SqlSession sqlSession = MyBatisUtil.getSqlSession();
/**
* 映射sql的标识字符串，
* me.gacl.mapping.orderMapper是orderMapper.xml文件中mapper标签的namespace属性的值，
* selectOrder是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
*/
String statement = "me.gacl.mapping.orderMapper.selectOrder";//映射sql的标识字符串
//执行查询操作，将查询结果自动封装成Order对象返回
Order order = sqlSession.selectOne(statement,);//查询orders表中id为的记录
//使用SqlSession执行完SQL之后需要关闭SqlSession
sqlSession.close();
System.out.println(order);//打印结果：Order [id=, orderNo=aaaa, price=.]
}
@Test
public void testGetOrderById(){
SqlSession sqlSession = MyBatisUtil.getSqlSession();
/**
* 映射sql的标识字符串，
* me.gacl.mapping.orderMapper是orderMapper.xml文件中mapper标签的namespace属性的值，
* selectOrderResultMap是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
*/
String statement = "me.gacl.mapping.orderMapper.selectOrderResultMap";//映射sql的标识字符串
//执行查询操作，将查询结果自动封装成Order对象返回
Order order = sqlSession.selectOne(statement,);//查询orders表中id为的记录
//使用SqlSession执行完SQL之后需要关闭SqlSession
sqlSession.close();
System.out.println(order);//打印结果：Order [id=, orderNo=aaaa, price=.]
}
}