一对一查询
我们这里做一个 用户表对订单表，即 一对一查询的需求：查询一个订单，与此同时查询出该订单所属的用户
我们准备工作 建表、Bean、核心配置文件、映射文件 这里省略，
执行命令：
然后我们Bean：
package com.bihu.Bean;
import java.util.Date;
public class User {
private int id;
private String username;
private String password;
private Date birthday;
public User() {
}
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;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
", birthday=" + birthday +
'}';
}
}
User
package com.bihu.Bean;
import java.util.Date;
public class Order {
private int id;
private Date ordertime;
private double total;
//当前订单属于哪一个用户
private 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;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@Override
public String toString() {
return "Order{" +
"id=" + id +
", ordertime=" + ordertime +
", total=" + total +
", user=" + user +
'}';
}
}
Order //重点是哪个user ，查询user表的数据是嵌进去的
mybetis核心配置文件：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="datasourceInfo.properties"></properties>
<typeAliases>
<typeAlias type="com.bihu.Bean.User" alias="User"></typeAlias>
<typeAlias type="com.bihu.Bean.Order" alias="Order"></typeAlias>
<typeAlias type="java.util.List" alias="List"></typeAlias>
</typeAliases>
<!-- 插件 -->
<plugins>
<plugin interceptor="com.github.pagehelper.PageHelper">
<property name="dialect" value="mysql"/>
</plugin>
</plugins>
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/bihu/mapper/UserMapper.xml"></mapper>
<mapper resource="com/bihu/mapper/OrderMapper.xml"></mapper>
</mappers>
</configuration>
mybatis 核心配置文件
⭐⭐⭐ 重点是映射文件这！！！
<?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.bihu.Dao.OrderMapper">
<resultMap id="orderMap" type="Order"> <!--Order已设置别名-->
<id column="oid" property="id"></id>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
<!-- 下面开始是User的封装-->
<result column="uid" property="user.id"></result>
<result column="username" property="user.username"></result>
<result column="password" property="user.password"></result>
<result column="birthday" property="user.birthday"></result>
</resultMap>
<select id="findAll" resultMap="orderMap"> <!--这的返回结果更改为上面自定义的结果集resultMap 因为里面有User对象-->
SELECT *,o.id oid FROM orders o,user u WHERE o.uid=u.id;
</select>
</mapper>
OrderMapper.xml
重点看注释即可
然后这里测试
注意测试里面的是Order对象，映射的也是Order文件
package com.bihu.Service;
import com.bihu.Bean.Order;
import com.bihu.Bean.User;
import com.bihu.Dao.OrderMapper;
import com.bihu.Dao.UserMapper;
import com.github.pagehelper.PageHelper;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class UserService {
public static void main(String[] args) throws IOException {
InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = build.openSession();
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for (Order item : all) {
System.out.println(item);
}
sqlSession.close();
}
}
Service 测试
运行：
作者：咸瑜
