MongoDB Aggregation group and count strings - mongodb

Question

I have a problem with counting different LogStatusses from my collection. I'd like the following result from a query:
Month | ImporterName | NrOfError | NrOfDebug | NrOfInfo | NrOfWarning
So this includes grouping by Month and ImporterName and counting the number of documents with the different statusses.
My MongoDB Collection:
{
"_id" : "8ec84cb7-5099-4a9d-be00-a40200a67c5a",
"Messages" : [
{
"LogStatus" : "Error",
"Message" : "My test message"
},
{
"LogStatus" : "Error",
"Message" : "My test message"
},
{
"LogStatus" : "Error",
"Message" : "My test message"
},
{
"LogStatus" : "Error",
"Message" : "My test message"
},
{
"LogStatus" : "Error",
"Message" : "My test message"
}
],
"StartTime" : new Date("2014-12-15T10:06:09.00Z"),
"EndTime" : new Date("2014-12-15T13:06:09.00Z"),
"HasErrors" : true,
"HasWarnings" : false,
"ImporterName" : "MyImporter"
}
I already have the following query's:
db.SessionLogItems.aggregate
([
{
$project:
{
month :{$month : "$StartTime"},
name: "$ImporterName",
status: "$Messages.LogStatus",
_id: 0
}
}
])
result:
month: 12, "name" : "importername", status: ["Error", "Error", "Info"]
and
db.SessionLogItems.aggregate
([
{
$unwind: "$Messages"
},
{
$group: { _id: "$Messages", Number : {$sum : 1 }}
},
{
$sort: {Number : -1 }
}
])
result:
"_id" : { "LogStatus" : "Warning", "Message" : "My test warning" }, "Number" :5
"_id" : { "LogStatus" : "Error", "Message" : "My test message" }, "Number" : 5
But I can't seem to figure out the correct query. Any help is appreciated!
EDIT:
My example above is just one out of many documents. I have several importers which have a startTime and EndTime. The importers have several logmessages and four possible LogStatusses: "Error", "Info", "Debug", "Warning". I'd like to have an overview per month and per importer how many errors, infos, debugs and warnings they produced.

Answer 1

Assuming there is no overlap in your "month" between StartTime and EndTime values then you can simply use the StartTime value as the basis for a grouping key. Most of the magic for your other "fields" comes from the $cond operator which decides whether to count the value or not:
db.SessionLogItems.aggregate([
// Unwind the array to de-normalize the documents contained
{ "$unwind": "$Messages" },
// Month and Importer form the grouping key
{ "$group": {
"_id": {
"month": { "$month": "$StartTime" },
"ImporterName": "$ImporterName"
},
"NrOfError": {
"$sum": {
"$cond": [
{ "$eq": [ "$Messages.LogStatus", "Error" ] },
1,
0
]
}
},
"NrOfDebug": {
"$sum": {
"$cond": [
{ "$eq": [ "$Messages.LogStatus", "Debug" ] },
1,
0
]
}
},
"NrOfInfo": {
"$sum": {
"$cond": [
{ "$eq": [ "$Messages.LogStatus", "Info" ] },
1,
0
]
}
},
"NrOfWarning": {
"$sum": {
"$cond": [
{ "$eq": [ "$Messages.LogStatus", "Warning" ] },
1,
0
]
}
}
}}
])
So basically the "Status" value is tested and where it is matched or not then the appropriate count value is added to the appropriate field.