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mongodbaggregation-frameworkmongodb-aggregation

get value from a filter result match

How do I get the value of a returned $filter match?

for example using this code ...

db.col.aggregate([
    {$project : {
        "Place"    : {$filter: {input: "$fields",as: "field",cond: { $eq: [ "$$field.name", "ABC" ]}}},
    }}
]);

I would get 

[{"name":"ABC" ,"value":"DEF"}]

as the value of Place. I am wondering how to get just the value (DEF)

Solution

  • Thanks to the comment from Yogesh, figured it out

    db.col.aggregate([
    {$project : {
        "Place"    : {$filter: {input: "$fields",as: "field",cond: { $eq: [ "$$field.name", "Place" ]}}},
    }},
    {$project : {
        "Place"    : {$arrayElemAt : ["$Place.value",0]}
    }}
]);

    ..wondering if there is a way to single-project it.