Mongodb find the Consecutive Failure Count - mongodb

Question

I have a dataset like this:
{
ip: 1.1.1.1,
process: 123,
type: failure,
date: 2021-04-01
},
{
ip: 1.1.1.2,
process: 124,
type: failure,
date: 2021-03-01
},
{
ip: 1.1.1.1,
process: 123,
type: failure,
date: 2021-02-01
},
{
ip: 1.1.1.1,
process: 123,
type: success,
date: 2021-01-01
}
How can I get the consecutive failure count for a given ip address and process? For example, given the dataset above, if I was to check how many times ip 1.1.1.1 has failed for process 123 before the last success I should get 2. However if the success record was the last record then I should get 0.
What I have so far is:
activityLog.find([
{
$match: {
ip: "1.1.1.1",
process: "123"
},
},
{
$sort: {
date: -1,
},
},
{
$limit: 10,
},
{
$project: {
_id: 0,
type: 1,
},
},
]);
This gives me a list of all types - sorted and matched

Answer 1

You can do the followings in an aggregation pipeline:
find the previous success record
do a self-lookup to find the fail records after the previous success record
do the count of the lookup of step 2
db.collection.aggregate([
{
$match: {
ip: "1.1.1.1",
process: "123",
type: "success"
}
},
{
"$sort": {
date: -1
}
},
{
$limit: 1
},
{
"$lookup": {
"from": "collection",
let: {
ip: "$ip",
process: "$process",
date: "$date"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$ip",
"$$ip"
]
},
{
$eq: [
"$process",
"$$process"
]
},
{
$lt: [
"$date",
"$$date"
]
},
{
$eq: [
"$type",
"success"
]
}
]
}
}
},
{
$sort: {
date: -1
}
},
{
$limit: 1
}
],
"as": "lastSuccess"
}
},
{
"$unwind": {
path: "$lastSuccess",
preserveNullAndEmptyArrays: true
}
},
{
"$lookup": {
"from": "collection",
let: {
ip: "$ip",
process: "$process",
date: {
$ifNull: [
"$lastSuccess.date",
ISODate("9999-12-31")
]
}
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$ip",
"$$ip"
]
},
{
$eq: [
"$process",
"$$process"
]
},
{
$gte: [
"$date",
"$$date"
]
},
{
$eq: [
"$type",
"failure"
]
}
]
}
}
}
],
"as": "previousFailures"
}
},
{
"$addFields": {
"lastFailuresCount": {
$size: "$previousFailures"
}
}
}
])
Here is the Mongo playground for your reference