CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-framework
John S
John S

Reputation: 231

Use $size on all documents in array MongoDB

Here's the structure part of my collection:

_id: ObjectId("W"),
names: [
    {
        number: 1,
        list: ["A","B","C"]
    },
    {
        number: 2,
        list: ["B"]
    },
    {
        number: 3,
        list: ["A","C"]
    }
    ...
],
...

I use this request:

db.publication.aggregate( [ { $match: { _id: ObjectId("54a1de90453d224e80f5fc60") } }, { $group: { _id: "$_id", SizeName: { $first: { $size: { $ifNull: [ "$names", [] ] } } }, names: { $first: "$names" } } } ] );

but I would now use $size in every documents of my names array.

Is it possible to get this result (where "sizeList" is the result of $size) :

_id: ObjectId("W"),
SizeName: 3,
names: [
    {
        SizeList: 3,
        number: 1,
        list: ["A","B","C"]
    },
    {
        SizeList: 1,
        number: 2,
        list: ["B"]
    },
    {
        SizeList: 2,
        number: 3,
        list: ["A","C"]
    }
    ...
],
...

Upvotes: 0

Views: 74

Answers (2)

Neil Lunn
Neil Lunn

Reputation: 151092

All you really want here is a $project stage and use $map to alter the contents of the array members:

db.names.aggregate([
    { "$project": {
        "SizeName": { "$size": "$names" },
        "names": { "$map": {
            "input": "$names",
            "as": "el",
            "in": {
                "SizeList": { "$size": "$$el.list" },
                "number": "$$el.number",
                "list": "$$el.list"
            }
        }}
    }}
])

You can alternately process with $unwind and group it all back again, but that's kind of long winded when you have MongoDB 2.6 anyway.

Upvotes: 4

Mark Dickson Jr.
Mark Dickson Jr.

Reputation: 598

This isn't necessarily the most efficient way, but I think it does what you're aiming to do:

db.publication.aggregate( [ 
    { $unwind: '$names' },
    { $unwind: '$names.list' },
    { $group: {
        _id: { _id: "$_id", number: "$names.number" },
        SizeList: { $sum: 1 },
        list: { $push: "$names.list" }
      }
    },
    { $group: {
        _id: "$_id._id",
        names: {
            $push: {
                number: "$_id.number",
                list: "$list",
                SizeList: "$SizeList"
            }
        },
        SizeName: {$sum: 1}
      }
    }
]);

Upvotes: 0

Related Questions