代码优化：遍历查询数据库代码优化

Posted 2022-05-27 root_zhb

遍历查询数据库代码优化

• SQL 映射 HashMap< String, List < T > >
• SQL 映射List< HashMap< String,String> >

场景：针对遍历查询数据库的两种场景做出优化，都是将多次遍历查询改为一条查询。
把数据库层面的 IO压力 转化为 代码层面的CPU和内存压力

SQL 映射 HashMap< String, List < T > >

1. 先查list，再stream分组
2. 搞个头行的实体类，resultMap返回

低效代码

for(TransportPlanningLines t:lines)
    List<TransportPlanningLines> transportPlanningLines = this.transportPlanningLinesRepository.select("transportPlanningNumber",t.getTransportPlanningNumber());
      

以先list再stream分组，优化后

//筛选出所有行id
List<String> collect = lines.stream().map(TransportPlanningLines::getTransportPlanningNumber).collect(Collectors.toList());
//查出所有得lineList
List<TransportPlanningLines> linesList = transportPlanningLinesMapper.selectTransportPlanningLines(collect);
//根据TransportPlanningNumber分组
Map<String, List<TransportPlanningLines>> collect1 = linesList.stream().collect(Collectors.groupingBy(TransportPlanningLines::getTransportPlanningNumber));

//配置合计数量
for(TransportPlanningLines t:lines)
    List<TransportPlanningLines> transportPlanningLines = collect1.get(t.getTransportPlanningNumber());

SQL 映射List< HashMap< String,String> >

参考资料：https://www.cnblogs.com/newbest/p/10018685.html
此处低效代码与上面类似，优化后如下

List<Long> collect = transportPlanningLines.stream().map(TransportPlanningLines::getRequiredPlanItemLinesId).collect(Collectors.toList());
List<HashMap<String, String>> longStringHashMap = requiredPlanItemLinesMapper.selectJtMaterialCodeAndComments(collect);

for(TransportPlanningLines t:transportPlanningLines)
    String manufactureFactory = t.getManufactureFactory();
    String weightWay = t.getWeightWay();
    String acceptanceQuantity = t.getAcceptanceQuantity().toString();
    for(HashMap<String, String> map:longStringHashMap)
        if(map.containsValue(t.getRequiredPlanItemLinesId()))
            String jtMaterialCode = map.get("jt_material_code");
            String comments = map.get("comments");
            //业务代码忽略
        
    

Mapper如下

List<HashMap<String,String>> selectJtMaterialCodeAndComments(@Param("list") List<Long> list);

SQL如下

<select id="selectJtMaterialCodeAndComments" resultType="java.util.HashMap">
    select
    rpil.required_plan_item_lines_id,
    rpil.comments,
    si.jt_material_code
    from scux_ynjt_required_plan_item_lines rpil
    left join smdm_item si on rpil.material_code=si.item_code
    WHERE
    rpil.required_plan_item_lines_id in
    <foreach collection="list" item="item" open="(" separator="," close=")">
        #item
    </foreach>
</select>

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