Mybatis的多表操作之一对一/多查询

Mybatis的多表操作

1、一对一查询

一对一查询的模型

用户表和订单标的关系为，一个用户有多个订单，一个订单只属于一个用户
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

测试订单

数据库中

mapper包下orderMapper类下

package com_mybatis_table.mapper;

import com_mybatis_table.pojo.Order;

import java.util.List;

public interface OrderMapper {

    //查询全部的方法
    public List<Order> findAll();

}

pojo包下的order类下

package com_mybatis_table.pojo;

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;
    }

//对应的get和set方法

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

pojo下user类下

package com_mybatis_table.pojo;

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

public class User {

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

    //描述的是当前用户存在哪些订单
    private List<Order> orderList;

//对应的get和set方法

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

OrderMapper.xml下

<?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_mybatis_table.mapper.OrderMapper">

    <resultMap id="orderMap" type="order">
        <!--手动指定字段与实体属性的映射关系
            column: 数据表的字段名称
            property：实体的属性名称
        -->
        <id column="oid" property="id"></id>
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>
       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">
         SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id
    </select>

</mapper>

sqlMapConfig.xml还是一样的配置，多出了引入OrderMapper.xml

    <!--加载映射文件-->
    <mappers>
         <mapper resource="com_mybatis/mapper/UserMapper_config.xml"></mapper>

         <mapper resource="com_mybatis/mapper/OrderMapper.xml"></mapper>
    </mappers>

MybatisTest测试代码下

public class MybatisTest {
    @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);
        }

        sqlSession.close();
    }
}

运行结果

查询操作运行结果

OrderMap.xml中也可使用

    <resultMap id="orderMap" type="order">
        <!--手动指定字段与实体属性的映射关系
            column: 数据表的字段名称
            property：实体的属性名称
        -->
        <id column="oid" property="id"></id>
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>
        <!--<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>-->

        <!--
            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)
        -->
        <association property="user" javaType="user">
            <id column="uid" property="id"></id>
            <result column="username" property="username"></result>
            <result column="password" property="password"></result>
            <result column="birthday" property="birthday"></result>
        </association>

    </resultMap>

单独的分离出来，结果也是一致的。

2、一对多查询

一对多查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只属于一个用户
一对多查询的需求：查询一个用户，与此同时查询出该用户具有的订单

UserMapper接口下

package com_mybatis_table.mapper;

import com_mybatis_table.pojo.User;

import java.util.List;

public interface UserMapper {

    public List<User> findAll();

}

UserMapper.xml下

<?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_mybatis_table.mapper.UserMapper">

    <resultMap id="userMap" type="user">
        <id column="uid" property="id"></id>
        <result column="username" property="username"></result>
        <result column="password" property="password"></result>
        <result column="birthday" property="birthday"></result>
        <!--配置集合信息
            property:集合名称
            ofType：当前集合中的数据类型
        -->
        <collection property="orderList" ofType="order">
            <!--封装order的数据-->
            <id column="oid" property="id"></id>
            <result column="ordertime" property="ordertime"></result>
            <result column="total" property="total"></result>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="userMap">
        SELECT *,o.id oid FROM USER u,orders o WHERE u.id=o.uid
    </select>

</mapper>

Mybatis测试下

    @Test
    public void test2() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.findAll();
        for (User user : userList) {
            System.out.println(user);
        }

        sqlSession.close();
    }

运行结果