MongoDB finding the document with more fields

Question

Is it possible to obtain, from a collection, the document with the highest amount of fields?

In this case, the returned value should be the second document or just 18.

Answer 1

You can use aggregation pipeline with $objectToArray stage starting from 3.4.4 version to convert all top key & value pair into document arrays followed by $group to find the $max with $size on keys.

db.collection.aggregate([{
    $project: {
        arrayofkeyvalue: {
            $objectToArray: "$$ROOT"
        }
    }
}, {
    $group: {
        _id: null,
        max: {
            $max: {
                $size: "$arrayofkeyvalue.k"
            }
        }
    }
}])