Agregating by field value on MongoDB - mongodb

Question

I have a collection composed of documents similar to one below:
{
"_id" : ObjectId("5dc916a72440b14b3f0ec096"),
"date" : ISODate("2019-11-11T11:07:03.968+03:00"),
"actions" : [
{
"type" : "Type1",
"action" : true
},
{
"type" : "Type2",
"action" : true
},
{
"type" : "Type3",
"action" : false
}
]
}
I am trying to count all the action types based on the boolean value of the actions.action property.
This is how I came so far:
db.Actions.aggregate(
{
$group: {
_id: {
year: { $year: "$date" },
month: { $month: "$date" },
day: { $dayOfMonth: "$date" },
},
count: { $sum: 1 }
}
}
);
As you can see this only gives me the count of the documents in the collection grouped by the action date.
What I need is something like this:
{
"_id" : {
"year" : 2019,
"month" : 10,
"day" : 13
},
"Type1": 300,
"Type2": 200,
"Type3": 120,
"count" : 305
}
Is this possible with a query or should I go in the direction of creating a cursor and agregating the values with it?

Answer 1

db.Actions.aggregate([
// Unwind to de-normalize the array
{ "$unwind": "$actions" },
// Group on both day and "type"
{ "$group": {
"_id": {
"date": {
"$toDate": {
"$subtract": [
{ "$toLong": "$date" },
{ "$mod": [{ "$toLong": { "$toDate": "$date" } }, 1000 * 60 * 60 * 24 ] }
]
}
},
"type": "$actions.type"
},
"total": { "$sum": { "$toLong": "$actions.action" } }
}},
// Roll-up the grouping to just by "day"
{ "$group": {
"_id": "$_id.date",
"data": { "$push": { "k": "$_id.type", "v": "$total" } }
}},
// Convert to key/value output
{ "$replaceRoot": {
"newRoot": {
"$mergeObjects": [
{ "_id": "$_id", "count": { "$sum": "$data.v" } },
{ "$arrayToObject": "$data" }
]
}
}}
])
To summarize:
The $unwind is needed simply because you want to "group" on a value which is inside an array of a document. Using this "de-normalizes", or essentially makes each array element into a new document for the same property and all other "parent" properties of the document in which that array resides. In simple speak, you get a "copy" of the containing document for every array member as a new document.
The next $group basically uses a "Date math" approach to rounding to a singular day. This is a bit prettier than methods like $year and $month etc, and actually returns a Date object, which you client language of choice will understand.
Of course this is a compound grouping key, meaning that the other part is of course the type field from the array of actions. And since you only want true results to count, we apply $toLong again in order to translate the Boolean into a numeric value to $sum ( which basically means "count" when it's 0 or 1 ). In older releases you could also do this using $cond, but the simple type conversion is a lot more simple to read for intent.
The rest of this is basically about translating to the expected "key/value"* output of the question. Really, you got the desired result in the very first $group operation but to be "key/value" you need to put all those results into an array ( by "date" of course ) using $push, and then convert that array into the root document using the $arrayToObject function.