循环中套查询优化

之前的想法是赋值的话是（无论是循环还是流式操作）在循环里面搜索完赋值，这是新手范的通病，建议不要再循环里面搜索赋值，这样的性能很差劲。
优化后的方法：结合本次业务 利用map集合 key存储主键 value存储数量

Repository:

/**
     * 查询创建人创建每个分组的人数集合
     * @param usrPid 创建人pid
     * @return
     */
    @Query("SELECT\n" +
            "model.pid,\n" +
            "COUNT(guser.groupDetailsPid)\n" +
            "FROM\n" +
            "GroupDetails model\n" +
            "LEFT JOIN GroupDetailsUser guser ON model.pid = guser.groupDetailsPid \n" +
            "WHERE\n" +
            "model.userPid = :usrPid\n" +
            "GROUP BY\n" +
            "model.pid")
    Stream<Object[]> userNum(String usrPid);

Service层

/**
     * 查询创建人创建每个分组的人数Map集合 String分组主键
     * @param usrPid 创建人pid
     * @return
     */
    @Transactional(readOnly = true)
    public Map<String,Long> userNum(String usrPid) {
        Map<String, Long> map = repository.userNum(usrPid)
                .collect(Collectors.toMap(arr->(String) arr[0], arr -> (long) arr[1]));
        return map;
    }

Controller层

涉及的代码：

Map<String, Long> countUsrs = service.userNum(getOperatorId());

 Page<GroupDetailsDTO> dataDto = data.map(groupDetails -> new GroupDetailsDTO(
                groupDetails.getPid(),
                groupDetails.getOrgPid(),
                groupDetails.getUserPid(),
                groupDetails.getGroupName(),
                groupDetails.getCreateTime(),
                groupDetails.getGroupDesc(),
                countUsrs.get(groupDetails.getPid())
        ));

全部代码

/**
     * 分页显示教师创建的分组
     * @param page
     * @param title 分组名称,默认值为""
     * @param startTime 起始时间
     * @param endTime 结束时间
     * @return
     */
    @GetMapping({"/group/details"})
    public ResponseEntity findAllByPage(@PageableDefault Pageable page,
                                        @RequestParam(required = false) String title,
                                        @RequestParam(required = false) @DateTimeFormat(pattern = "yyyy-MM-dd") LocalDate startTime,
                                        @RequestParam(required = false) @DateTimeFormat(pattern = "yyyy-MM-dd") LocalDate endTime) {
        if (startTime != null && endTime != null && startTime.isAfter(endTime)) {
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(Translator.toLocale("group.time.Failed.message"));
        }
        LocalDateTime startLocalDateTime = null;
        LocalDateTime endLocalDateTime = null;
        if (startTime != null || endTime != null) {
            startLocalDateTime = LocalDateTime.of(startTime, LocalTime.of(0, 0));
            endLocalDateTime = LocalDateTime.of(endTime, LocalTime.of(23, 59));
        }
        Map<String, Long> countUsrs = service.userNum(getOperatorId());
        Page<GroupDetails> data = service.findAllByPage(getOperatorId(), title, startLocalDateTime, endLocalDateTime, page);
        Page<GroupDetailsDTO> dataDto = data.map(groupDetails -> new GroupDetailsDTO(
                groupDetails.getPid(),
                groupDetails.getOrgPid(),
                groupDetails.getUserPid(),
                groupDetails.getGroupName(),
                groupDetails.getCreateTime(),
                groupDetails.getGroupDesc(),
                countUsrs.get(groupDetails.getPid())
        ));
        return ResponseEntity.ok(dataDto);
    }