Multiple Counts with single query in mongodb

问题:

I am new to Mongo Db and would appreciate some help with this query. I have been sifting through posts here for the past couple of days tearing my hair to see if I could find anything related to my query but with no luck.

I have a collection with documents similar in structure to below :

_id: xyz
Movieid: 123
MovieName: Titanic
ReleaseDate: 2000-01-01

_id: uvw
Movieid: 456
MovieName: Titanic II
ReleaseDate: 2018-01-01

_id: pqr
Movieid: 789
MovieName: Titanic III
ReleaseDate: 

I would like to achieve the output as counts for totalmovies, movies with release date, and movies without release date in 3 seperate columns as below:

Total   |   Released  |     UnReleased
 3      |       2     |          1

I was able to write individual queries to execute the counts, but I am unable to successfully consolidate all that into a single query. The end goal is to create one view producing these counts as output. I have tried using operators such as $and, but can't seem to get the query to work as desired....this is as far as I got :

db.getCollection("Movies").aggregate(
    $and: [
{ 
            "$match" : 
                {"ReleaseDate":{$exists:true}}
            }
        , 
        { 
            $count:"Total"
        },
        { 
            "$match" : 
                {"ReleaseDate":{$exists:true,$nin:[""]}}
            }
        , 
        { 
            $count:"Released"
        },

        { 
            "$match" : 
                {"ReleaseDate":{$exists:true,$in:[""]}}
            }
        , 
        { 
            $count:"Unreleased"
        }


    ]
);

回答1:

You can try below $facet aggregation

$count aggregation will always give you the counts for only single matching ($match) condition. So you need to further divide your each count into multiple section and that's what the $facet provides by processes multiple aggregation pipelines within a single stage on the same set of input documents.

db.collection.aggregate([
  { "$facet": {
    "Total": [
      { "$match" : { "ReleaseDate": { "$exists": true }}},
      { "$count": "Total" },
    ],
    "Released": [
      { "$match" : {"ReleaseDate": { "$exists": true, "$nin": [""] }}},
      { "$count": "Released" }
    ],
    "Unreleased": [
      { "$match" : {"ReleaseDate": { "$exists": true, "$in": [""] }}},
      { "$count": "Unreleased" }
    ]
  }},
  { "$project": {
    "Total": { "$arrayElemAt": ["$Total.Total", 0] },
    "Released": { "$arrayElemAt": ["$Released.Released", 0] },
    "Unreleased": { "$arrayElemAt": ["$Unreleased.Unreleased", 0] }
  }}
])

Ouput

[{
    "Total": 3,
    "Released": 2,
    "Unreleased": 1
}]

回答2:

You can use below aggregation.

$gt > null - to check whether field exists or not in aggregation expressions.

$cond with $sum to output 0 and 1 based on release date filter.

$add to add both released and unreleased count to output total.

db.Movies.aggregate([
 {"$group":{
   "_id":null,
   "Unreleased":{"$sum":{"$cond":[{"$and":[{"$gt":["$ReleaseDate",null]},{"$ne":["$ReleaseDate",""]}]},0,1]}},
   "Released":{"$sum":{"$cond":[{"$and":[{"$gt":["$ReleaseDate",null]},{"$ne":["$ReleaseDate",""]}]},1,0]}}
 }},
 {"$addFields":{"Total":{"$add":["$Unreleased","$Released"]}}}
])

回答3:

db.Movies.aggregate(

    // Pipeline
    [
        // Stage 1
        {
            $group: {
                _id: null,
                Total: {
                    $sum: 1
                },
                docs: {
                    $push: '$$ROOT'
                }
            }
        },

        // Stage 2
        {
            $project: {
                _id: 0,
                Total: 1,
                Released: {
                    $filter: {
                        input: "$docs",
                        as: "doc",
                        cond: {
                            $ne: ["$$doc.ReleaseDate", ""]
                        }
                    }
                },
                Unreleased: {
                    $filter: {
                        input: "$docs",
                        as: "doc",
                        cond: {
                            $eq: ["$$doc.ReleaseDate", ""]
                        }
                    }
                },
            }
        },

        // Stage 3
        {
            $project: {
                Total: 1,
                Released: {
                    $size: '$Released'
                },
                UnReleased: {
                    $size: '$Unreleased'
                }
            }
        },

    ]



);