Sum array in aggregation query - mongodb

Question

I'm pretty new to MongoDB, and having some problems getting my query as I want it. The documents contain "errors" that have happened a specific time. The result I want from the query is an error count for each month per user. This I have already figured out, but additionally I want the total errorcount per user.
This is what I've got so far:
db.Logger.aggregate([
{ "$group": {
"_id": {
"name": "$name",
"month": { "$month": "$errorTime" }
},
"totalErrors": { "$sum": 1 }
}},
{ $group :
{ _id: { name : "$_id.name"},
errors: { $addToSet: { totalErrors: { errorsThisMonth: "$totalErrors", currentMonth : "$_id.month" } } },
}
}
])
The result is:
{
"_id" : {
"name" : "abhos"
},
"errors" : [
{
"totalErrors" : {
"errorsThisMonth" : 6,
"currentMonth" : 2
}
},
{
"totalErrors" : {
"errorsThisMonth" : 6,
"currentMonth" : 1
}
}
]
},
Will it be possible to get what I want by adding to that query?

Answer 1

All you need is an additional $sum in your second $group:
db.Logger.aggregate([
{ "$group": {
"_id": {
"name": "$name",
"month": { "$month": "$errorTime" }
},
"totalErrors": { "$sum": 1 }
}},
{ "$group": {
"_id": "$_id.name",
"errors": {
"$addToSet": {
"errorsThisMonth": "$totalErrors",
"currentMonth" : "$_id.month"
}
},
"totalErrors": { "$sum": "$totalErrors" }
}}
])
Also you have a few extra document levels you do not need in there, such as extra fields under the _id and the "errors" "set" produced in the grouping. This output is just a little different without those additional levels:
{
"_id": "abhos"
"errors" : [
{
"errorsThisMonth" : 6,
"currentMonth" : 2
},
{
"errorsThisMonth" : 6,
"currentMonth" : 1
}
],
"totalErrors": 12
},