Mybatis实体类和表映射问题(推荐)

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(20), 
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+ "]";
}
}

<&＃63;xml version="1.0" encoding="UTF-8" &＃63;>





select * from orders where order_id=#{id}



select order_id id, order_no orderNo,order_price price from orders where order_id=#{id}



select * from orders where order_id=#{id}

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 Test2 {
@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,1);//查询orders表中id为1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 testGetOrderById2(){
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,1);//查询orders表中id为1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=1, orderNo=aaaa, price=23.0]
}
@Test
public void testGetOrderById3(){
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,1);//查询orders表中id为1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=1, orderNo=aaaa, price=23.0]
}
}