Map mongo aggregation result to array

Question

I have a mongo query that looks like this:

db.myCollection.aggregate([ { 
    $group: { 
        _id: null,
        price: {
            $sum: "$price"
        },
        inventory: {
            $sum: "$inventory"
        }
    }
}])

Which returns

{
    "_id" : null,
    "price" : 26,
    "inventory" : 5,
}

I would like a query which would rather return something like this:

[
    {
        name: "price",
        amount: 26
    },
    {
        name: "inventory",
        amount: 5
    }
]

EDIT: How would I write this in Java with Spring Data? I can group and sum but don't know how to project it?

Aggregation aggregation = newAggregation(
                group("$id")
                        .sum("price").as("price")
                        .sum("inventory").as("inventory")
);

Caconde · Accepted Answer · 2019-08-12 21:02:52Z

1

You'll need to use $project. It allows us to define which fields will be returned, as well as their format.

db.myCollection.aggregate([{ 
    $group: { 
        _id: null,
        price: {
            $sum: "$price"
        },
        inventory: {
            $sum: "$inventory"
        }
    }
},
{
    $project: {
        _id: 0 //removes _id from result
        something: [
            {name: "price", amount: "$price"},
            {name: "inventory", amount: "$inventory"}
        ]    
    }
}])

That will give you:

{
    "something" : [ 
        {
            "name" : "price",
            "amount" : 26
        }, 
        {
            "name" : "inventory",
            "amount" : 5
        }
    ]
}

answered Aug 12, 2019 at 21:02

Caconde

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2 Comments

davo Over a year ago

Thanks! Any idea how to convert this to a Spring query? Updated my post

Caconde Over a year ago

Sorry, man. Unfortunately, I don't have any experience on Spring.

Ashh · Accepted Answer · 2019-08-13 09:48:29Z

0

You can use below aggregation

db.collection.aggregate([
  { "$project": {
    "data": {
      "$map": {
        "input": { "$objectToArray": "$$ROOT" },
        "in": { "name": "$$this.k", "amount": "$$this.v" }
      }
    }
  }},
  { "$unwind": "$data" },
  { "$replaceRoot": { "newRoot": "$data" }},
  { "$match": { "amount": { "$ne": null }}
  }
])

answered Aug 13, 2019 at 9:48

Ashh

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