Aggregate with a Composite Key - mongodb

Question

I am trying to aggregate some data and group it by Time Intervals as well as maintaining a sub-category, if you will. I want to be able to chart this data out so that I will have multiple different Lines corresponding to each Office that was called. The X axis will be the Time Intervals and the Y axis would be the Average Ring Time.
My data looks like this:
Calls: [{
created: ISODate(xyxyx),
officeCalled: 'ABC Office',
answeredAt: ISODate(xyxyx)
},
{
created: ISODate(xyxyx),
officeCalled: 'Office 2',
answeredAt: ISODate(xyxyx)
},
{
created: ISODate(xyxyx),
officeCalled: 'Office 3',
answeredAt: ISODate(xyxyx)
}];
My goal is to get my calls grouped by Time Intervals (30 Minutes/1 Hour/1 Day) AND by the Office Called. So when my aggregate completes, I'm looking for data like this:
[{"_id":TimeInterval1,"calls":[{"office":"ABC Office","ringTime":30720},
{"office":"Office2","ringTime":3070}]},
{"_id":TimeInterval2,"calls":[{"office":"Office1","ringTime":1125},
{"office":"ABC Office","ringTime":15856}]}]
I have been poking around for the past few hours and I was able to aggregate my data, but I haven't figured out how to group it properly so that I have each time interval along with the office data. Here is my latest code:
Call.aggregate([
{$match: {
$and: [
{created: {$exists: 1}},
{answeredAt: {$exists: 1}}]}},
{$project: { created: 1,
officeCalled: 1,
answeredAt: 1,
timeToAns: {$subtract: ["$answeredAt", "$created"]}}},
{$group: {_id: {"day": {"$dayOfYear": "$created"},
"hour": {
"$subtract": [
{"$hour" : "$created"},
{"$mod": [ {"$hour": "$created"}, 2]}
]
},
"officeCalled": "$officeCalled"
},
avgRingTime: {$avg: '$timeToAns'},
total: {$sum: 1}}},
{"$group": {
"_id": "$_id.day",
"calls": {
"$push": {
"office": "$_id.officeCalled",
"ringTime": "$avgRingTime"
},
}
}},
{$sort: {_id: 1}}
]).exec(function(err, results) {
//My results look like this
[{"_id":118,"calls":[{"office":"ABC Office","ringTime":30720},
{"office":"Office 2","ringTime":31384.5},
{"office":"Office 3","ringTime":7686.066666666667},...];
});
This just doesn't quite get it...I get my data but it's broken down by Day only. Not my 2 hour time interval that I was shooting for. Let me know if I'm doing this all wrong, please --- I am VERY NEW to aggregation so your help is very much appreciated.
Thank you!!

Answer 1

All you really need to do is include the both parts of the _id value your want in the final group. No idea why you thought to only reference a single field.
Also "loose the $project" as it is just wasted cycles and processing, when you can just use directly in $group on the first try:
Call.aggregate(
[
{ "$match": {
"created": { "$exists": 1 },
"answeredAt": { "$exists": 1 }
}},
{ "$group": {
"_id": {
"day": {"$dayOfYear": "$created"},
"hour": {
"$subtract": [
{"$hour" : "$created"},
{"$mod": [ {"$hour": "$created"}, 2]}
]
},
"officeCalled": "$officeCalled"
},
"avgRingTime": {
"$avg": { "$subtract": [ "$answeredAt", "$created" ] }
},
"total": { "$sum": 1 }
}},
{ "$group": {
"_id": {
"day": "$_id.day",
"hour": "$_id.hour"
},
"calls": {
"$push": {
"office": "$_id.officeCalled",
"ringTime": "$avgRingTime"
},
},
"total": { "$sum": "$total" }
}},
{ "$sort": { "_id": 1 } }
]
).exec(function(err, results) {
});
Also note the complete omission of $and. This is not needed as all MongoDB query arguments are already "AND" conditions anyway, unless specifically stated otherwise. Just stick to what is simple. It's meant to be simple.