Mybatis之ResultMap的使用

前言

一直在使用mybatis但一直没有好好使用过resultMap,最近写了一个考试系统,处理用户历史答题记录的时候,发现使用resultMap更方便一点

代码(可以跳过看结论)

pojo类

import cn.ims.exam.entity.Title;
import cn.ims.exam.entity.TitleAnswer;

import java.util.List;

public class TitlePo extends Title {

    private Integer userId;
    private List answerIds;
    private String num;
    private String typeName;
    private List answers;

    public String getNum() {
        return num;
    }

    public void setNum(String num) {
        this.num = num;
    }

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public List getAnswerIds() {
        return answerIds;
    }

    public void setAnswerIds(List answerIds) {
        this.answerIds = answerIds;
    }

    public String getTypeName() {
        return typeName;
    }

    public void setTypeName(String typeName) {
        this.typeName = typeName;
    }

    public List getAnswers() {
        return answers;
    }

    public void setAnswers(List answers) {
        this.answers = answers;
    }
}

resultMap设置(其中num为自定义的字段,它不和数据库中的字段关联,只用于接受传入的参数后传递给查询selectAllAnswerChecked)

Mapper:
List selectItems(@Param("po")UserItemPo po);

Mapper.xml:

        SELECT
        t.id,
        t.title,
        t.type,
        #{po.userId} as userId,
        #{po.num} as num
        FROM title t
        
            LEFT JOIN user_type ut ON ut.id = t.type_id
            JOIN (
            SELECT ROUND(
            RAND() * ((SELECT MAX(id)
            FROM title where valid = '0' and type_id = #{po.userTypeId}) - (SELECT MIN(id)
            FROM title where valid = '0' and type_id = #{po.userTypeId})) - 40
            ) AS id
            ) AS t2
            WHERE  t.id > t2.id and t.valid = '0' and type_id = #{po.userTypeId}
            LIMIT 40
        
        
            WHERE t.id IN(
            
                #{id}
            
            )
        
    

 
        SELECT
            ta.id,
            ta.name
        FROM title_answer ta
        WHERE title_id = #{id}
    

    
        SELECT a.answer_id
        FROM user_answer a
        WHERE a.title_id = #{id} AND a.user_id = #{userId} and a.num = #{num}
    

结论

以上代码可以返回考试题目列表(包括每个题目的答案列表,以及每个题目考生的答案列表)
其中:

• 可以设置自定义字段用于参数传递(num)
• 可以设置自定义列表进行相关查询(即一对多的对应关系处理)
• 注意collection中的参数传递为 column(参数名=对应result的column)