MongoDB - Subtracting Double in Aggregation Pipeline - mongodb

Question

I'll start with the part of the query that's not working right.
{$project: {"date":"$_id.date",
"location":"$data.location",
"coachgroup":"$data.coachgroup",
"staffedcoaches":"$data.staffedcoaches",
"allots":{
$cond: [
{$eq: [
"$data.coachgroup","Default"
]},
{$floor: [
{$subtract:
[NumberInt("$data.staffcoaches"),
{$divide:
["$data.virtualheads",
"$data.ratio"
]}
]}
]},
"$data.allots"
]}
}
},
So, the "staffedcoaches" field is a Double. "virtualheads" and "ratio" are both Int32. "staffedcoaches" is derived from a count much earlier in the query. When I try to use it as-is in the subtraction, the result is null. When I try to use it with NumberInt() as shown below the staffedcoaches becomes a 0. Number() and NumberLong() are no more successful.
To take just one document as an example, the "ratio" is 15 and the staffedcoaches is 4. So the result should be 11. But I can only get a null or a -15.
Is there a way to get the Double treated as an Integer so I can complete this operation?
Thanks for reading

Answer 1

I figured out the answer. While the calculation wouldn't work in $project, it did work as an $addFields. (You may notice I took out the conditional. With or without it makes no difference. The only impacting factor was moving the calculations from $project to $addFields.)
{$project: {"date":"$_id.date",
"location":"$data.location",
"coachgroup":"$data.coachgroup",
"staffedcoaches":"$data.staffedcoaches"
},
{$addFields: {
"allots":{
$floor:[
{$subtract:
["$staffedcoaches",
{$divide:
["$virtualheads","$ratio"]}
]}]
}}},