find overlapping dates within mongoDB array objects - arrays

Question

I have a MongoDB document collection with multiple arrays that looks like this :
{
"_id": "1235847",
"LineItems": [
{
"StartDate": ISODate("2017-07-31T00:00:00.000+00:00"),
"EndDate": ISODate("2017-09-19T00:00:00.000+00:00"),
"Amount": {"$numberDecimal": "0.00"}
},
{
"StartDate": ISODate("2022-03-20T00:00:00.000+00:00"),
"EndDate": ISODate("2022-10-21T00:00:00.000+00:00"),
"Amount": {"$numberDecimal": "6.38"}
},
{
"StartDate": ISODate("2022-09-20T00:00:00.000+00:00"),
"EndDate": ISODate("9999-12-31T00:00:00.000+00:00"),
"Amount": {"$numberDecimal": "6.17"}
}
]
}
Is there a simple way to find documents where the startdate has overlapped with previously startdate, enddate?
The startdate can not be before previous end dates within the array
The start/end can not be between previous start/end dates within the array
The below works but I don't want to hardcode the array index to find all the documents
{
$match: {
$expr: {
$gt: [
'LineItems.3.EndDate',
'LineItems.2.StartDate'
]
}
}
}

Answer 1

Here's one way you could find docs where "StartDate" is earlier than the immediately previous "EndDate".
db.collection.find({
"$expr": {
"$getField": {
"field": "overlapped",
"input": {
"$reduce": {
"input": {"$slice": ["$LineItems", 1, {"$size": "$LineItems"}]},
"initialValue": {
"overlapped": false,
"prevEnd": {"$first": "$LineItems.EndDate"}
},
"in": {
"overlapped": {
"$or": [
"$$value.overlapped",
{"$lt": ["$$this.StartDate", "$$value.prevEnd"]}
]
},
"prevEnd": "$$this.EndDate"
}
}
}
}
}
})
Try it on mongoplayground.net.