mongodb - 如何在 pymongo 管道中创建日期时间对象？

Question

我有一些代码在其中设置了以下管道：过滤器集合、项目年和月、按年和月分组，然后以 YYYY-MM-01 之类的日期时间对象结束。

示例文档：

{
  _id: 123456
  foo: "bar"
  dt: ISODate("2015-12-24T11:59:00Z")
}

示例代码：

from pymongo import MongoClient
db = client.testDB
posts = db.testCollection
pipeline = [
  {"$match": {"foo":"bar"}},
  {"$project": {
      "year": {"$year": "$dt"},
      "month": {"$month": "$dt"},
    }
  },
  {"$group": {
      "_id": { "dt": ??? },
      "totalCount": { "$sum": 1 }
    }
  },
  {"$out": "myResults"}
}
posts.aggregate(pipeline)

目标：

{
  _id: {dt: ISODate("2015-12-01T00:00:00Z")}
  totalCount: 8
}

Answer 1

为了将日期投影到本月的第一天，例如转换2015-12-24为2015-12-01，我修改了此页面上的代码如下：

示例文档：

{
  _id: 123456
  foo: "bar"
  dt: ISODate("2015-12-24T11:59:00Z")
}

代码：

from pymongo import MongoClient
db = client.testDB
posts = db.testCollection
pipeline = [
  {"$match": {"foo":"bar"}},
  {
    "$project": {
      "dt": "$dt"
      "d": {"$dayOfMonth": "$dt"},
      "h": {"$hour": "$dt"},
      "m": {"$minute": "$dt"},
      "s": {"$second": "$dt"},
      "ml": {"$millisecond": "$dt"},
    }
  },
  {
    "$group": {
      "_id": {
        "$subtract": [
          "$dt",
          {
            "$add": [
              "$ml",
              {"$multiply": ["$s", 1000]},
              {"$multiply": ["$m", 60, 1000]},
              {"$multiply": ["$h", 60, 60, 1000]},
              {"$multiply": [{"$subtract": ["$d", 1]}, 24, 60, 60, 1000]},
            ]
          }
        ] 
      },
      "totalCount": { "$sum": 1 }
    }
  },
  {"$out": "myResults"}
}