如何操作聚合管道中的日期字段? [英] How can I manipulate a date field in an aggregation pipeline?

问题描述

我正在尝试设置从日期字段到一天开始的时间

I'm trying to set the time from a Date field to the start of the day

function getDate(date){ return new Date(date.getYear(), date.getMonth(), 
date.getDate(), 0,0,0); }
...
{"$project" : {
    "_id"   : getDate("$dt"),
...

• 如果我发送"$dt"，则在传递字符串时会得到TypeError: date.getYear is not a function，

  • If I send "$dt" I get TypeError: date.getYear is not a function as I'm passing a string,

    如果删除引号，我得到Error: "$dt is not defined"

    If remove the quotation marks, I get Error: "$dt is not defined",

    那么如何将日期对象传递给函数?

    So how do I pass the date object to the function?

    推荐答案

    MongoDB的聚合管道不支持JavaScript.要为汇总管道中的结果操作日期值，您需要使用日期汇总运算符.

    MongoDB's aggregation pipeline does not support JavaScript. To manipulate date values for results in the aggregation pipeline you need to use Date Aggregation Operators.

    例如:

    db.date.aggregate([
        { $project: {
             _id: { $dateToString: { format: "%Y%m%d", date: "$dt" }}
        }}
    ])
    

    假设您有一个文档，该文档的字段名为dt，日期值为ISODate("2017-07-01T10:01:23.344Z")，结果将如下所示:

    Assuming you have a document with a field called dt with a date value of ISODate("2017-07-01T10:01:23.344Z"), the result would look like:

    {
      "result": [
    
        {
          "_id": "20170701"
        }
    
      ],
      "ok": 1
    }
    

    注意:如果同一天有多个文档，则此方法将在结果中创建重复的_id值.您可能需要投影到其他字段名称，或者使用 $group 阶段，而不是$project阶段，如果您打算合并同一天的值.

    Note: if you have multiple documents for the same day, this approach will create duplicate _id values in your results. You may want to project to a different field name or perhaps use a $group stage instead of $project if your intent is to combine values for the same day.

    这篇关于如何操作聚合管道中的日期字段?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！