Mongodb Aggregation Pipeline Count Total size across multiple fields - mongodb

Question

`"ActivityScores" : {
"Spring" : [
{
"ActivityId" : "8fd38724-7e7d-4518-bd49-d38a8b4b3435",
"ActivityTime" : "2017-05-25T16:07:02.000-06:00"
}
],
"Winter" : [
{
"ActivityId" : "90d2a976-19d9-4ce0-aa88-d32c122d173b",
"ActivityTime" : "2017-02-14T22:50:00.000-06:00"
}
],
"Fall" : [
{
"ActivityId" : "84b8c41e-788f-4acd-abec-dc455285972b",
"ActivityTime" : "2016-11-15T22:37:02.000-06:00"
},
{
"ActivityId" : "157af880-d47b-42fc-8ecf-ecfc1bbb56b1",
"ActivityTime" : "2016-09-01T22:50:05.000-06:00"
}
]
},
"Grade" : "2",
"GradeTag" : "GRADE_2", `
I am looking for aggregation query to get Total of ActivityIds. I tried various combination of $group, $unwind, $size $addToset but none of them seems to be working . I need to find total activities using aggregation framework only. I don't want to go through each document using javascript or python to get the total counts. Is there any easy way around?

Answer 1

Thanks.We are on version 3.2.Finally below combination worked. ActivityScores was field to entity.SchoolYears in our Schema.Working Aggregation Pipeline for me.
db.studentcontentareadocument.aggregate(
[
{
$project: {
"SpringActivitiesPerDoc" : {
"$size" : "$entity.SchoolYears.ActivityScores.Spring"
},
"WinterActivitiesPerDoc" : {
"$size" : "$entity.SchoolYears.ActivityScores.Winter"
},
"FallActivitiesPerDoc" : {
"$size" : "$entity.SchoolYears.ActivityScores.Fall"
}
}
},
{
$project: {
"TotalActivitiesPerDoc" : {
"$add" : [
"$SpringActivitiesPerDoc",
"$WinterActivitiesPerDoc",
"$FallActivitiesPerDoc"
]
}
}
},
{
$group: {
"_id" : null,
"TotalActivities" : {
"$sum" : "$TotalActivitiesPerDoc"
}
}
},
{
$project: {
"_id" : 0,
"TotalSGPActivities" : "$TotalActivities"
}
}
],
{
cursor: {
batchSize: 50
},
allowDiskUse: true
}
);