mysatis中子查询剖析

mybatis中查询代码是这样写的

 <resultMap id="riskDTOMap" type="vip.xiaonuo.modular.safety.risk.common.entity.dto.SafetyAllRiskListDTO">
       <result column="id" property="id"></result>
       <result column="org_id" property="orgId"></result>
       <result column="inspect_type" property="inspectType"></result>
       <result column="risk_level" property="riskLevel"></result>
       <result column="responsible_user" property="responsibleUser"></result>
       <result column="risk_descript" property="riskDescript"></result>
       <result column="risk_photo" property="riskPhoto"></result>
       <result column="risk_status" property="riskStatus"></result>
       <result column="create_time" property="createTime"></result>
       <result column="create_user" property="createUser"></result>
       <result column="rectification_time" property="rectificationTime"></result>
       <result column="orgName" property="orgName"></result>
       <result column="responsibleUserName" property="responsibleUserName"></result>
       <result column="createUserName" property="createUserName"></result>
       <result column="risk_name" property="riskName"></result>
       <result column="risk_name_id" property="riskNameId"></result>
        <collection property="recordListDTOS"
                    ofType="vip.xiaonuo.modular.safety.risk.common.entity.dto.SafetyAllRiskRecordListDTO"
                    select="selectRecordDTOs"
                    column="{riskId=id}"/>
    </resultMap>
    
 <select id="selectAllRiskList" resultMap="riskDTOMap">
        SELECT
        risk.id, risk.org_id,risk.inspect_type,risk.risk_level,risk.responsible_user,risk.risk_descript,risk.risk_photo,
        risk.risk_status,risk.create_time,risk.create_user,risk.rectification_time,rname.risk_name,rname.id risk_name_id,
        org.`name` orgName,U1.name responsibleUserName,U2.name createUserName
        FROM
        `safety_risk` risk
        LEFT JOIN
        sys_org org on  risk.org_id = org.id
        LEFT JOIN
        sys_user U1 on U1.id = risk.responsible_user
        LEFT JOIN
        sys_user U2 on U2.id = risk.create_user
        LEFT JOIN
        safety_risk_name rname on risk.risk_name_id = rname.id
        <where>
            <if test="null != riskParam.createUserName and riskParam.createUserName != ''">
                and u2.name like concat('%',#{riskParam.createUserName},'%')
            </if>
            <if test="null != riskParam.riskLevel">
                and risk_level = #{riskParam.riskLevel}
            </if>
            <if test="null != riskParam.riskName and ''!= riskParam.riskName">
                and rname.id =  #{riskParam.riskName}
            </if>
            <if test="null != riskParam.riskStatus">
                and risk_status = #{riskParam.riskStatus}
            </if>
            <if test="null != riskParam.inspectType">
                and inspect_type = #{riskParam.inspectType}
            </if>
            <if test="null != riskParam.orgIds and riskParam.orgIds.size > 0">
                and org_id in
                <foreach collection="riskParam.orgIds" item="e" open="(" close=")" separator=",">
                    #{e}
                </foreach>
            </if>
            <if test="null != riskParam.riskStatues and riskParam.riskStatues.size > 0">
                and risk_status in
                <foreach collection="riskParam.riskStatues" item="e" open="(" close=")" separator=",">
                    #{e}
                </foreach>
            </if>
            <if test="null != riskParam.id">
                and risk.id = #{riskParam.id}
            </if>
            <if test="null != riskParam.ids and riskParam.ids.size > 0">
                and risk.id in
                <foreach collection="riskParam.ids" item="e" open="(" close=")" separator=",">
                    #{e}
                </foreach>
            </if>
            <if test="null != riskParam.createUser">
                and risk.create_user = #{riskParam.createUser}
            </if>
            <if test="null != riskParam.responsibleUser ">
                and risk.responsible_user = #{riskParam.responsibleUser}
            </if>
            <if test="null != riskParam.checkTimeStart and riskParam.checkTimeStart != ''">
                and risk.create_time &gt;= #{riskParam.checkTimeStart}
            </if>
            <if test="null != riskParam.checkTimeEnd and riskParam.checkTimeEnd != ''">
                and risk.create_time &lt;= #{riskParam.checkTimeEnd}
            </if>
            <if test="null != riskParam.rectificationTimeStart and riskParam.rectificationTimeStart != ''">
                and rectification_time &gt;= #{riskParam.rectificationTimeStart}
            </if>
            <if test="null != riskParam.rectificationTimeEnd and riskParam.rectificationTimeEnd != ''">
                and rectification_time &lt;= #{riskParam.rectificationTimeEnd}
            </if>
        </where>
        order by
        risk.create_time desc
    </select>
    
 <select id="selectRecordDTOs" resultType="vip.xiaonuo.modular.safety.risk.common.entity.dto.SafetyAllRiskRecordListDTO">
        SELECT
                safety_risk_record.id recordId,
                risk_id,
                rectification_measure,
                rectification_photo,
                check_status,
                check_descript,
                completion_time,
                delay_day,
                delay_status,
                delay_remark,
                safety_risk_record.create_time recordCreateTime,
                safety_risk_record.create_user,
                safety_risk_record.update_time,
                safety_risk_record.update_user,
                F1.file_object_name rectificationPhotoPath
        from
            safety_risk_record
        LEFT JOIN
            sys_file_info F1 on F1.id = safety_risk_record.rectification_photo
        where
            risk_id = #{riskId}
    </select>

返回实体类

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package vip.xiaonuo.modular.safety.risk.common.entity.dto;

import com.fasterxml.jackson.annotation.JsonFormat;
import lombok.Data;

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

/**
 * 隐患整改
 *
 * @author Eternal
 * @date 2022-09-27 09:21:16
 */
@Data
public class SafetyAllRiskListDTO {
    /**
     * 主键
     */
    private Long id;

    /**
     * 组织机构ID
     */
    private Long orgId;

    /**
     * 组织机构名称
     */
    private String orgName;

    /**
     * 隐患名称
     */
    private String riskName;

    private Long riskNameId;
    /**
     * 检查类型
     */
    private Integer inspectType;

    /**
     * 隐患级别
     */
    private Integer riskLevel;

    /**
     * 整改责任人id
     */
    private Long responsibleUser;

    /**
     * 整改责任人
     */
    private String  responsibleUserName;

    /**
     * 整改责任人Account
     */
    private String responsibleAccount;

    /**
     * 整改期限
     */
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date rectificationTime;

    /**
     * 隐患描述
     */
    private String riskDescript;

    /**
     * 隐患照片
     */
    private String riskPhoto;

    /**
     * 整改核查id
     */
    private Long recordId;

    /**
     * 隐患状态
     */
    private Integer riskStatus;

    /**
     * 检查人姓名
     */
    private String createUserName;

    /**
     * 创建时间
     */
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date createTime;

    /**
     * 创建人
     */
    private Long createUser;

    /**
     * 更新时间
     */
    private Date updateTime;

    /**
     * 更新人
     */
    private Long updateUser;

    /**
     * 整改核查列表信息
     */
    private List<SafetyAllRiskRecordListDTO> recordListDTOS;

}

先说结论

再mybatis中这样写子查询，和在循环中写select通过外键查询效果是一样的，效率很低，速度很慢。
通过测试，他有一个懒加载的机制
再例子中：只有用到了recordListDTOS 才会执行子查询

可以看到，这条sql的执行时间不到1s，打印的sql日志也只有主体sql
但是当循环取recordListDTOS时：
打印了一千多条sql进行外键查询，耗时17s

真是坑爹啊▄█▀█●