Mongo aggregation: Count documents based on array field matching condition - mongodb

Question

I am trying to collects some statistics from a mongo collection using an aggregation pipeline but can not seem to solve my issue.
I have a collection of documents looking like this.
{
_id: “36723678126”,
dates: [ 2020-03-10T10:17:48.799Z, 2020-03-10T08:46:50.347Z, 2019-07-11T13:16:17.294Z ]
}
I would like count the number of documents that meet the following conditions
At least one date in the last 30 days
No dates between 60 and 30 days ago
At least one date before 60 days ago
Would really appreciate any help! :)

Answer 1

This should solve the problem (https://mongoplayground.net/p/B3LbEo8UaHA):
Test data:
[
{
_id: 1,
dates: [
ISODate("2020-03-10T10:17:48.799Z"),
ISODate("2020-03-10T08:46:50.347Z"),
ISODate("2019-07-11T13:16:17.294Z")
]
},
{
_id: 2,
dates: [
ISODate("2020-04-10T10:17:48.799Z"),
ISODate("2020-05-10T08:46:50.347Z"),
ISODate("2019-10-11T13:16:17.294Z")
]
}
]
Query:
db.collection.aggregate([
// create the new fields based on the date rules and count occurences of array
{
$addFields: {
"last_30_days": {
$sum: {
$map: {
"input": "$dates",
"as": "d",
"in": {
$cond: {
"if": {
$lte: [
"$$d",
{
$subtract: [
"$$NOW",
2592000000 // 30 days
]
}
]
},
"then": 1,
"else": 0
}
}
}
}
},
"between_30_60": {
$sum: {
$map: {
"input": "$dates",
"as": "d",
"in": {
$cond: {
"if": {
$and: [
{
$lt: [
"$$d",
{
$subtract: [
"$$NOW",
2592000000 // days
]
}
]
},
{
$gt: [
"$$d",
{
$subtract: [
"$$NOW",
5184000000 // 60 days
]
}
]
}
]
},
"then": 1,
"else": 0
}
}
}
}
},
"last_60_days": {
$sum: {
$map: {
"input": "$dates",
"as": "d",
"in": {
$cond: {
"if": {
$lte: [
"$$d",
{
$subtract: [
"$$NOW",
5184000000
]
}
]
},
"then": 1,
"else": 0
}
}
}
}
}
}
},
// find which document meet the conditions (1 for true, 0 for false)
{
$project: {
"meet_conditions": {
$cond: {
"if": {
$and: [
{
$gt: [
"$last_30_days", // at least one occurence
0
]
},
{
$eq: [
"$between_30_60", // no occurences
0
]
},
{
$gt: [
"last_60_days", // at least one occurence
0
]
}
]
},
"then": 1,
"else": 0
}
}
}
},
// count documents, summing the meet_conditions field (because they are 0 or 1)
{
$group: {
_id: null,
count: {
$sum: "$meet_conditions"
}
}
}
])
Result:
[
{
"_id": null,
"count": 1
}
]
So in the example above, there's just one documents that meet your conditions.
Obs.: To calculate the days you have to do (the bold numbers are the day you want):
1 * 1000 * 60 * 60 * 24 * 30 = 2592000000ms = 30 days
1 * 1000 * 60 * 60 * 24 * 60 = 5184000000ms = 60 days