The process of determining array.reduce between two collections in MongoDb

Question

The process of determining array.reduce between two collections in MongoDb

I have two MongoDB collections with a one-to-one relationship. I want to perform an array.reduce operation based on both of these collections, like so:

CollectionA: [
  { _id: 1, valueA: 234, idB: 1 },
  { _id: 2, valueA: 64, idB: 2 },
  { _id: 3, valueA: 456, idB: 3 },
]

CollectionB: [
  { _id: 1, valueB: 678 },
  { _id: 2, valueB: 11 },
  { _id: 3, valueB: 4005 },
]

I want to calculate the sum of:

sum(valueA - valueB)

Is it possible to achieve this with a single database request? If not, what is the most elegant approach?

javascript mongodb

Answer 1

Answer №1

To achieve the desired results, you can utilize the aggregation-pipeline in MongoDB.

Here is a sample query structure for your reference:

db.CollectionA.aggregate([
    {
        $lookup: {
            from: 'B',
            localField: 'idB',
            foreignField: '_id',
            as: 'objB'
        }
    },
    { $unwind: '$objB' },
    {
        $project: {
            subField: {
                $subtract: ['$valueA', '$objB.valueB']
            }
        }
    },
    {
        $group: {
            _id: null,
            sum: {
                $sum: '$subField'
            }
        }
    },
    {
        $project: {
             totalSum: 1
        }
    }
]);

Answer 2

To achieve the desired results, you can utilize the aggregation-pipeline in MongoDB.

Here is a sample query structure for your reference:

db.CollectionA.aggregate([
    {
        $lookup: {
            from: 'B',
            localField: 'idB',
            foreignField: '_id',
            as: 'objB'
        }
    },
    { $unwind: '$objB' },
    {
        $project: {
            subField: {
                $subtract: ['$valueA', '$objB.valueB']
            }
        }
    },
    {
        $group: {
            _id: null,
            sum: {
                $sum: '$subField'
            }
        }
    },
    {
        $project: {
             totalSum: 1
        }
    }
]);

The process of determining array.reduce between two collections in MongoDb

Answer №1

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