mongodb的mapreduce分组统计

//根据in_time（yyyy-MM-dd HH:mm:ss）字段精确到天分组，统计数量
Criteria criteria = Criteria.where("parking_id").is(inParking.getParking_id())
        .and("in_time").gte(inParking.getStart_time())
        .lte(inParking.getEnd_time());
String map = "function(){emit(this.in_time.substring(0,13),{count:1});}";
String reducef = "function(key,values){var total = 0;for(var i=0;i mapReduceResults =
        mongoTemplate.mapReduce(query, "in_parking", map, reducef, BasicDBObject.class);
Iterator iterator = mapReduceResults.iterator();
while (iterator.hasNext()) {
    String jsonString = iterator.next().toString();
    JSONObject jsonObject = JSONObject.parseObject(jsonString);
//有个Bug,有时返回结果value是JSONObject对象 有时直接返回统计值
    if(jsonString.contains("count")){
        JSONObject valueObj = jsonObject.getJSONObject("value");
        Object count = valueObj.get("count");
        jsonObject.put("value",count);
    }
    jsonArray.add(jsonObject);
}

reduce的处理条数超过100时会用两个reduce处理  第二次调reduce函数时 total会重新初始化 然后抛异常

将reduce函数改下如下方式：

 

String reducef = "function(key,values){var total = {count:0};for(var i=0;i