Get sum of Nested Array in Aggregate - mongodb

Question

Ok, I have an issue I cannot seem to solve.
I have a document like this:
{
"playerId": "43345jhiuy3498jh4358yu345j",
"leaderboardId": "5b165ca15399c020e3f17a75",
"data": {
"type": "EclecticData",
"holeScores": [
{
"type": "RoundHoleData",
"xtraStrokes": 0,
"strokes": 3,
},
{
"type": "RoundHoleData",
"xtraStrokes": 1,
"strokes": 5,
},
{
"type": "RoundHoleData",
"xtraStrokes": 0,
"strokes": 4
}
]
}
}
Now, what I am trying to accomplish is using aggregate sum the strokes and then order it afterwards. I am trying this:
var sortedBoard = db.collection.aggregate(
{$match: {"leaderboardId": boardId}},
{$group: {
_id: "$playerId",
played: { $sum: 1 },
strokes: {$sum: '$data.holeScores.strokes'}
}
},
{$project:{
type: "$SortBoard",
avgPoints: '$played',
sumPoints: "$strokes",
played : '$played'
}}
);
The issue here is that I do net get the strokes sum correct, since this is inside another array.
Hope someone can help me with this and thanks in advance :-)

Answer 1

You need to say $sum twice:
var sortedBoard = db.collection.aggregate([
{ "$match": { "leaderboardId": boardId}},
{ "$group": {
"_id": "$playerId",
"SortBoard": { "$first": "$SortBoard" },
"played": { "$sum": 1 },
"strokes": { "$sum": { "$sum": "$data.holeScores.strokes"} }
}},
{ "$project": {
"type": "$SortBoard",
"avgPoints": "$playeyed",
"sumPoints": "$strokes",
"played": "$played"
}}
])
The reason is because you are using it both as a way to "sum array values" and also as an "accumulator" for $group.
The other thing you appear to be missing is that $group only outputs the fields you tell it to, therefore if you want to access other fields in other stages or output, you need to keep them with something like $first or another accumulator. We also appear to be missing a pipeline stage in the question anyway, but it's worth noting just to be sure.
Also note you really should wrap aggregation pipelines as an official array [], because the legacy usage is deprecated and can cause problems in some language implementations.
Returns the correct details of course:
{
"_id" : "43345jhiuy3498jh4358yu345j",
"avgPoints" : 1,
"sumPoints" : 12,
"played" : 1
}