MyBatis复杂映射开发之一对一查询

本文介绍了一对一查询需求下的用户表和订单表关系，展示了如何查询一个订单并同时查询出对应的用户信息。通过创建 User 和 Order 实体，并建立关联，实现了订单和用户信息的查询功能。

# 一对一查询需求

用户表和订单表的关系为：一个用户可以有多个订单，一个订单只能从属于一个用户

一对一查询需求：查询一个订单，同时查询出该订单所对应的用户

对应的 sql 语句：select * from orders o,user u where o.uid=u.id

查询结果如下：

id	ordertime	total	uid	id	username	password	birthday
1	2022-03-17 17:15:33	3000	1	1	lucy	123	2022-03-17 17:15:56
2	2022-03-17 17:15:33	4000	1	1	lucy	123	2022-03-17 17:15:56
3	2022-03-17 17:15:33	5000	2	2	tom	123	2022-03-17 17:15:56

# 需求分析

# 具体实现

# 创建 User 和 Order 实体

User

/**
 * 用户信息
 *
 * @name: User
 * @author: terwer
 * @date: 2022-03-17 17:41
 **/
public class User {
    private Integer id;
    private String username;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

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

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Order

/**
 * 订单
 *
 * @name: Order
 * @author: terwer
 * @date: 2022-03-17 17:42
 **/
public class Order {
    private Integer id;
    private String orderTime;
    private Double total;

    // 代表当前订单属于哪一个用户
    private User user;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getOrderTime() {
        return orderTime;
    }

    public void setOrderTime(String 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 +
                '}';
    }
}

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# 创建 OrderMapper 接口

/**
 * 订单映射
 *
 * @name: IUserMapper
 * @author: terwer
 * @date: 2022-03-17 17:54
 **/
public interface OrderMapper {
    /**
     * 查询订单同时查询订单所属用户
     * @return
     */
    public List<Order> findOrderAndUser();
}

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# 配置 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.terwergreen.mapper.OrderMapper">
    <resultMap id="orderMap" type="com.terwergreen.pojo.Order">
        <result property="id" column="id"></result>
        <result property="orderTime" column="ordertime"></result>
        <result property="total" column="total"></result>

        <association property="user" javaType="com.terwergreen.pojo.User">
            <result property="id" column="uid"></result>
            <result property="username" column="username"></result>
        </association>
    </resultMap>

    <!-- resultMap：手动配置实体属性与表字段的映射关系 -->
    <select id="findOrderAndUser" resultMap="orderMap">
        select * from orders o,user u where o.uid=u.id
    </select>
</mapper>

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另外一种配置方法

 <mapper namespace="com.terwergreen.mapper.OrderMapper">
    <resultMap id="orderMap" type="com.terwergreen.pojo.Order">
       <result property="id" column="id"></result>
        <result property="orderTime" column="ordertime"></result>
        <result property="total" column="total"></result>
    
        <result property="user.id" column="uid"></result>
        <result property="user.username" column="username"></result>
    </resultMap>
  
    <!-- resultMap：手动配置实体属性与表字段的映射关系 -->
    <select id="findOrderAndUser" resultMap="orderMap">
        select * from orders o,user u where o.uid=u.id
    </select>
</mapper>

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# 测试结果

@Test
public void test1() throws IOException {
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

    SqlSession sqlSession = sqlSessionFactory.openSession();
    OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);

    List<Order> orderList = orderMapper.findOrderAndUser();
    for (Order order : orderList) {
        System.out.println(order);
    }
}