How to subtract from current field in mongodb with update using aggregation pipeline?

Question

Basically I want to subtract the value from total and update it by subtracted value.

db.invoice.update({ "_id": ObjectId(req.params.id) },
    { "$set": { "total": total - 200 } }, function (err, doc) {
        if (err) return new Error(err);
        if (doc.result.n > 0) {
            console.log(" Invoice updated with Payment info.", doc.result);
        } else {
            console.log("Something went wrong while payment info updation.")
        }
});

I don't know how to achieve this here. I found $mul operator for multiplication with current field but I didn't find $sub operator in mongodb. I found $subtract aggregation but I am unable to use $subtract with update().

Could someone help me? Please

Thanks

Answer 1

You can use $inc operator with the negative value.

db.invoice.update({ "_id": ObjectId(req.params.id) },
    { "$inc": { "total": -200 } }, function (err, doc) {
        if (err) return new Error(err);
        if (doc.result.n > 0) {
            console.log(" Invoice updated with Payment info.", doc.result);
        } else {
            console.log("Something went wrong while payment info updation.")
        }
});