CODEWITHSUNDEEP
pythonmongodbaggregation-framework
FLATeric
FLATeric

Reputation: 91

MongoDB aggregating from objects in array to object by specific field

I would like to convert this type of document (objects in array):

[{"name": "david", "props": {"prop1": {"AR": 9, "NY": 8}, "prop2": 
{"AR": 10, "NY": 9}}},
{"name": "john", "props": {"prop1": {"AR": 7, "NY": 8}, "prop2": {"AR": 
8, "NY": 9}}}]

into this one (filtering by the 'AR' field):

{"david": {"prop1": 9, "prop2": 10}, "john": {"prop1": 7, "prop2": 8}}

using MongoDB aggregations. Any thoughts?

Upvotes: 1

Views: 367

Answers (1)

mickl
mickl

Reputation: 49975

There are two really helpful operators: $objectToArray which converts an object into an array of k-v pairs and $arrayToObject which converts that array back to an object. So you should use first one, reshape your objects and then use second one. So having a document like this:

{ 
    array: [
        {"name": "david", "props": {"prop1": {"AR": 9, "NY": 8}, "prop2": {"AR": 10, "NY": 9}}},
        {"name": "john", "props": {"prop1": {"AR": 7, "NY": 8}, "prop2": {"AR": 8, "NY": 9}}}
    ] 
}

You can use below aggregation:

db.col.aggregate([
    {
        $project: {
            output: {
                $arrayToObject: {
                    $map: {
                        input: "$array",
                        as: "doc",
                        in: {
                            k: "$$doc.name",
                            v: {
                                $arrayToObject: {
                                    $map: {
                                        input: { $objectToArray: "$$doc.props" },
                                        as: "prop",
                                        in: { k: "$$prop.k", v: "$$prop.v.AR" }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
])

Which outputs:

{ "_id" : ..., "output" : { "david" : { "prop1" : 9, "prop2" : 10 }, "john" : { "prop1" : 7, "prop2" : 8 } } }

Upvotes: 1

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