MongoDB compare endTime with startTime of next document - mongodb

Question

I have a similar collection where I have sort them by their startTime:
{"name": 'A', "startTime": '1634626355', "endTime": '1634631405'}
{"name": 'A', "startTime": '1634631406', "endTime": '1634631864'}
{"name": 'A', "startTime": '1634631865', "endTime": '1634656048'}
{"name": 'A', "startTime": '1634712642', "endTime": '1634718856'}
How can I compare the documents such that if the document endTime and the next document startTime duration is less than 5 minutes, merge it.
This is the result I'm trying to achieve (The 1st 3 documents are merged into 1 where it uses the startTime of the 1st document and the endTime of the 3rd document):
{"name": 'A', "startTime": '1634626355', "endTime": '1634656048'}
{"name": 'A', "startTime": '1634712642', "endTime": '1634718856'}
Thanks

Answer 1

First of all, you should never store date/time values as string, it's a design flaw. Store always proper Date object.
This solution works without self-lookup, so it may perform better:
db.collection.aggregate([
{
$set: {
startDateTime: { $toDate: { $multiply: ["$startTime", 1000] } },
endDateTime: { $toDate: { $multiply: ["$endTime", 1000] } }
},
},
{ $sort: { startDateTime: 1 } },
{ $group: { _id: null, data: { $push: "$$ROOT" } } },
{
$set: {
data: {
$reduce: {
input: "$data",
initialValue: [],
in: {
$cond: {
if: {
$or: [
{ $eq: [{ $size: "$$value" }, 0] }, // for the initail element
{
$gt: [
{
$dateDiff: { // calculate difference
endDate: "$$this.startDateTime",
startDate: { $last: "$$value.endDateTime" },
unit: "minute"
}
},
5 // more than 5 Minutes
]
}
]
},
then: { $concatArrays: ["$$value", ["$$this"]] }, // append new element
else: {
$map: {
input: "$$value",
as: "data",
in: {
$cond: {
if: { $eq: ["$$data._id", { $last: "$$value._id" }] }, // find last element
then: { // update last element
$mergeObjects: [
"$$data",
{ endDateTime: "$$this.endDateTime" },
{ endTime: "$$this.endTime" }
]
},
else: "$$data"
}
}
}
}
}
}
}
}
}
},
// some cosmetic
{ $unwind: "$data" },
{ $replaceRoot: { newRoot: "$data" } }
])
Mongo Playground

Answer 2

You can use $lookup in an aggregation pipeline to find out the documents that you need to remove. Then, perform a forEach to remove them.
db.collection.aggregate([
{
$addFields: {
endDateTime: {
"$toDate": {
"$multiply": [
{
$toLong: "$endTime"
},
1000
]
}
}
},
},
{
"$lookup": {
"from": "collection",
let: {
end: "$endDateTime"
},
pipeline: [
{
"$addFields": {
startDateTime: {
"$toDate": {
"$multiply": [
{
$toLong: "$startTime"
},
1000
]
}
}
}
},
{
$match: {
$expr: {
$and: [
{
$lte: [
{
$subtract: [
"$startDateTime",
"$$end"
]
},
300000
]
},
{
$lte: [
"$$end",
"$startDateTime"
]
}
]
}
}
}
],
"as": "lessThan5min"
}
},
{
"$unwind": "$lessThan5min"
},
{
"$replaceRoot": {
"newRoot": "$lessThan5min"
}
}
]).forEach(function(doc){
db.collection.remove({ "_id": doc._id });
});
Here is the Mongo playground to find out the documents that you need to remove for your reference.