MongoDB aggregate sum returns invalid result - node.js

Question

This is MongoDB Tabe I am using when it tries to calculate the sum qty it returns the wrong result and I don't know why
┌─────────┬───────────────┬───────┬─────────┬────────┐
│ (index) │ code │ qty │ product │ branch │
├─────────┼───────────────┼───────┼─────────┼────────┤
│ 0 │ '114=>115-41' │ 0.34 │ '4009' │ '1' │
│ 1 │ '114=>115-41' │ -0.02 │ '4009' │ '1' │
│ 2 │ '114=>115-41' │ -0.06 │ '4009' │ '1' │
│ 3 │ '114=>115-41' │ -0.12 │ '4009' │ '1' │
│ 4 │ '114=>115-41' │ -0.14 │ '4009' │ '1' │
└─────────┴───────────────┴───────┴─────────┴────────┘
The query:
let AggreArray=[
{
$group:{
_id: {
code:"$code",
product:"$product",
branch:"$branch",
},
qty: {$sum: "$qty" },
}
}
]
db.coll.aggregate(AggreArray).toArray((err, result) => {
console.log(result);
});
instead of returning qty: 0 it returns
[
{
_id: {
product: 5fec20bc26b1650017003f4a,
code: '114=>115-41',
branch: 5fec43f269cdbd300ccf9275
},enter code here
qty: 2.7755575615628914e-17, // expected 0
}
]
instead of returning qty: 0 it returns Qty: 2.775575.
and I don't know why plz help me I was trying to fix it all mayday and I cannot.

Answer 1

In MongoDB all numbers are 64-bit floating-point double values, by default. The NumberDecimal type is used to explicitly specify 128-bit decimal-based floating-point values capable of emulating decimal rounding with exact precision. This data type can give you the desired result of 0(zero).
That is, in your aggregation you need to convert the qty to a NumberDecimal type. This is a two step process - first the number is to be converted to a string type, and then to the NumberDecimal type (this is because the NumberDecimal constructor expects a string as its parameter).
So, your aggregation works with the following changes to return a result of 0 (zero):
db.coll.aggregate([
{
$match: {
product: ObjectId('5fec20bc26b1650017003f4a'),
code: '114=>115-41',
branch: ObjectId('5fec43f269cdbd300ccf9275'),
}
},
{
$addFields: { qty: { $toDecimal: { $toString: "$qty" } } }
},
{
$group:{
_id: { code:"$code", product:"$product", branch:"$branch" },
qty: { $sum: "$qty" },
}
},
{
$addFields: { qty: { $toDouble: "$qty" } }
}
])
NOTE: In MongoDB NodeJS Driver, NumberDecimal is represented as Decimal128.