CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-framework
Olaf Erlandsen
Olaf Erlandsen

Reputation: 6036

How to transform documents to key-value?

Well, I have documents with this strcuture:

{
    "x" : "X1",
    "y" : 10
},
{
    "x" : "X2",
    "y" : 22
},
{
    "x" : "...",
    "y" : 42
}

So, how I can convert all results to:

{
    "X1" : 10,
    "X2" : 22,
    "X3" : 42
}

I trying with $arrayToObject and $map, but this dont work

Thanks!

This collection have arround 50 millions docs.

Upvotes: 0

Views: 119

Answers (1)

mickl
mickl

Reputation: 49945

Assuming your collection is small enough so that an output of following operation won't exceed 16MB BSON limit, you can use below aggregation:

db.col.aggregate([
    {
        $group: {
            _id: null,
            docs: {
                $push: {
                    k: "$x",
                    v: "$y"
                }
            }
        }
    },
    {
        $replaceRoot: {
            newRoot: {
                $arrayToObject: "$docs"
            }
        }
    }
])

$arrayToObject expects objects having two properties k and v. To promote that object to a root level you can use $replaceRoot operator.

Upvotes: 1

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