mybatis与stream使用小记

1-mybatis解决limit语句限制

This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery异常解决方法

例子1:mybatis-plus 1层子查询嵌套，mysql不支持LIMIT/IN/ANY/SOME

// 查询最近100条数据
List<SendNsqMessageDO> allfeeYopProtocolDTOs = sendNsqMessageMapper.selectList(
        new QueryWrapper<SendNsqMessageDO>()
                .inSql("id","select id  from send_nsq_message  order by  created_at desc limit 100")
);

解决办法：2层子查询

// 查询最近100条数据
List<SendNsqMessageDO> allfeeYopProtocolDTOs = sendNsqMessageMapper.selectList(
new QueryWrapper<SendNsqMessageDO>()
.inSql("id","select t.id from (select * from send_nsq_message order by created_at desc limit 100) as t")
);

2-stream快速实现求和

目的：结合mybatis查询结果，快速求和

 

普通解决办法：求出列的List，然后遍历相加，求和

 

简化版：

int oweQuotaSum = alldebtRecords.stream().mapToInt(t->Math.toIntExact(t.getOweQuota())).sum();
int oweQuotaSnapshotSum = alldebtRecords.stream().mapToInt(t->Math.toIntExact(t.getOweQuotaSnapshot())).sum();
int recoveryQuotaSum = alldebtRecords.stream().mapToInt(t->Math.toIntExact(t.getRecoveryQuota())).sum();