How to convert an array inside Mongodb document to JsonArray

Question

I'm trying to convert the "interesse" array into a new object with 2 fields "term" which is the current array terms and a statistic value with the name "str" with a starting value of 0
as the following example. my database currently has about 16KK entries so i'm trying to create some sort of function or routine to deal with it.

Original documents

{
    "email" : "[email protected]",
    "interesse" : [ 
        "Calcados", 
        "Acessorios para viagem", 
        "Interesse em noticias sobre curiosidades"
    ],
    "data" : "2017-01-30"
}

{
    "email" : "[email protected]",
    "interesse" : [ 
        "Eletrodomesticos e portateis", 
        "Geladeiras"
    ],
    "data" : "2017-01-30"
}

Result documents

{
    "email" : "[email protected]",
    "interesse" : [ 
        {"term":"Calcados","str":0}, 
        {"term":"Acessorios para viagem","str":0},
        {"term":"Interesse em noticias sobre curiosidades","str":0}
    ],
    "data" : "2017-01-30"
}

{
    "email" : "[email protected]",
    "interesse" : [ 
        {"term":"Eletrodomesticos e portateis","str":0}, 
        {"term":"Geladeiras","str":0},
    ],
    "data" : "2017-01-30"
}

I was looking at arrayToObject.. but the function only transforms the entire array into a single object... what i want is to transform each value into new object...

mickl · Accepted Answer · 2020-05-11 21:28:51Z

2

You need $addFields to replace existing field and $map to transform your current array:

db.collection.aggregate([
    {
        $addFields: {
            interesse: {
                $map: {
                    input: "$interesse",
                    in: {
                        term: "$$this", str: 0
                    }
                }
            }
        }
    }
])

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answered May 11, 2020 at 21:28

mickl

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2 Comments

fils capo Over a year ago

Great! thanks! didnt know how to use map. can you xplain the meaning of $$this for me?

mickl Over a year ago

@filscapo when using $map you can use as to explicity name the variable which represents currently processed element but you can also skip it as it default to this (docs.mongodb.com/manual/reference/operator/aggregation/map/…)

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