在Mongo DB中查询带有条件的子元素的数量 [英] Query the count of sub elements with condition in Mongo DB

问题描述

我是Mongo DB的新手，并希望在以下查询任务中获得一些帮助.

I am new to Mongo DB and would appreciate some help with the following query task.

我有一组如下所示的文档:

I have a collection of documents that looks like below:

{
    "field_1" : {
      "subfield_1" : {
        "subsubfield_1" : "true",
        "subsubfield_2" : "false",
        "subsubfield_3" : "true"
        },
      "subfield_2" : "sf2"
      },
    "field_2" : {
      "subfield_1" : {
        "subsubfield_1" : "true",
        "subsubfield_2" : "false"
        },
      "subfield_2" : "sf2"
      },
    "field_3" : {
      "subfield_1" : {
        "subsubfield_1" : "true",
        "subsubfield_2" : "false",
        "subsubfield_3" : "false"
        },
      "subfield_2" : "sf2"
      }
}

我正在尝试查询，以便我为集合中的每个元素(1)确切指定要返回的字段(在这种情况下为subfield_1和subfield_2，而(2)仅用于subfield_1返回true个元素的计数.所以我希望输出看起来像这样:

And I am trying to query such that I, for each element in the collection (1) specify exactly which fields to return (in this case subfield_1 and subfield_2, and, (2) for subfield_1only return the count of trueelements. So I would like the output to look like:

{
  {
    "subfield_1" : 2,
    "subfield_2" : "sf2"
  },
  {
    "subfield_1" : 1,
    "subfield_2" : "sf2"
  },
  {
    "subfield_1" : 1,
    "subfield_2" : "sf2"
  }
}

我一直在尝试这段代码，但这只给了我subfield_1中每个元素的条目数:

I have been trying this code but that only gives me the number of entries in subfield_1for each element:

db.getCollection('myCollection').aggregate(
  {
  $match: {<some other condition>}
  },
  {
  $project: {
    subfield_2: 1, 
    subfield_1: {'$size': '$subfield_1'}
  }
  }
)

提前谢谢！

推荐答案

您需要运行 $ objectToArray 将嵌套的构造函数转换为键和值的数组，然后使用 $ filter 仅获取true值:

You need to run $objectToArray to transform your nested structer into an array of keys and values and then use $unwind to get a separate document for every sub-document. Then you can run another $objectToArray along with $filter to get only true values:

db.collection.aggregate([
    {
        $project: {
            doc: { $objectToArray: "$$ROOT" }
        }
    },
    {
        $unwind: "$doc"
    },
    {
        $match: { $expr: { $ne: [ "$doc.k", "_id" ] } }
    },
    {
        $project: {
            _id: 0,
            subfield_1: { $size: { $filter: { input: { $objectToArray: "$doc.v.subfield_1" }, cond: { $eq: [ "$$this.v", "true" ] } } } },
            subfield_2: "$doc.v.subfield_2"
        }
    }
])

蒙戈游乐场

这篇关于在Mongo DB中查询带有条件的子元素的数量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！