How can I find the sum and average of a document array? - mongodb

Question

Currently, I have the following document structure. The range field holds sub JSON objects as an array.
{
"_id" : ObjectId("62f60ba0ed0f1a1a0v"),
"userId" : "1431",
"range" : [
{
"index" : 0,
"clubType" : "driver",
"swingSize" : "full",
"distance" : 200,
"createdAt" : "2022-08-12T08:13:20.435+00:00"
},
{
"index" : 0,
"clubType" : "driver",
"swingSize" : "full",
"distance" : 150,
"createdAt" : "2022-08-12T08:13:20.435+00:00"
},
{
"index" : 0,
"clubType" : "wood",
"swingSize" : "full",
"distance" : 180,
"createdAt" : "2022-08-12T08:13:20.435+00:00"
}
]
}
In the above document, I want to sum and average the indexes with the same clubType and swingSize. So I used mongoose Aggregate like below.
result = await ClubRangeResultSchema.aggregate([
{
$match : {
userId : "1431",
range : {
$elemMatch : {
$and : [
{
createdAt : { $gte : lastDate }
},
{
createdAt : { $lte : lastDate }
}
]
}
}
}
},
{
$group : {
'_id' : {
'clubName' : '$range.clubName',
'swingSize' : '$range.swingSize'
},
'totalDistance' : { $sum : { $sum : '$range.distance' }}
}
}
]);
The result of the above query is all duplicate field names, and the total is also extracted for all data.
How should I modify the query?

Answer 1

You're close but need to do a couple of changes:
you want to $unwind the range array, $group doesn't flattern the array so when you use $range.clubType you are basically grouping the array itself as the value.
You want an additional match after the $unwind, the $elemMatch you use does not filter the range object, it does matches the initial document.
After the changes the pipeline should look like this:
db.collection.aggregate([
{
$match: {
userId: "1431",
range: {
$elemMatch: {
createdAt: "2022-08-12T08:13:20.435+00:00"
}
}
}
},
{
$unwind: "$range"
},
{
$match: {
"range.createdAt": "2022-08-12T08:13:20.435+00:00"
}
},
{
$group: {
"_id": {
"clubName": "$range.clubType",
"swingSize": "$range.swingSize"
},
"totalDistance": {
$sum: "$range.distance"
},
avgDistance: {
$avg: "$range.distance"
}
}
}
])
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