How to search by sum of fields in mongodb?

Question

MongoDB

The user enters the total area, then a search is performed by matching the total area. But here's the problem, there is no total area in the collection, there are several different areas, and they need to be summed up. How can I write down what I got?

query = {
    $lte: {
        {$sum: ["$area", "$businessArea", "$sgArea", "$forestArea"]} : maxArea
    },
    $gte: {
        {$sum: ["$area", "$businessArea", "$sgArea", "$forestArea"]} : minArea
    }
};

Answer 1

db.test.drop();
db.test.insert([
    {_id: 1, "area": 1, "brea": 2},
    {_id: 2, "area": 3, "brea": 4}]);
db.test.aggregate([
    {$project: {"a": ["$area", "$brea"]}},
    {$unwind: "$a"},
    {$group: {_id: "$_id", "a": {$sum: "$a"}}},
    {$match: {"a": {$gt: 5, $lt: 10}}}
]);

Answer 2

Keep the total area in the document - simpler and works orders of magnitude faster on large collections.