Mongoose - How to query field in the last object of an array of objects - node.js

Question

I have MongoDB documents structured like this:
{
"_id": "5d8b987f9f8b9f9c8c8b9f9",
"targetsList": [
{
"target": "user",
"statusList": [
{
"date": "2018-01-01",
"type": "OK"
},
{
"date": "2018-01-02",
"type": "FAILD"
}
]
}
]
}
And I want to count all documents that in their "targetList" array, there is an object with "target"=="user" - and also that object conatin on the last element of its "statusList" array, an object with "type" != "FAILD".
Any ideas on how to implement this kind of query?
Mongo playground:
https://mongoplayground.net/p/3bCoHRnh-KQ
In this example, I expected the count to be 1, because only the second object meets the conditions.

Answer 1

An aggregation pipeline
1st step - Filtering out where "targetsList.target": "user"
2nd step - $unwind on targetsList to get it out of array
3rd step - getting the last element of the targetsList.statusList array using $arrayElemAt
4th step - getting the results where that last element is not FAILD
5th step - getting the count
demo - you can try removing parts of the pipeline to see what the intermediate results are
db.collection.aggregate([
{
$match: {
"targetsList.target": "user"
}
},
{
$unwind: "$targetsList"
},
{
$project: {
"targetsList.statusList": {
$arrayElemAt: [
"$targetsList.statusList",
-1
]
},
}
},
{
$match: {
"targetsList.statusList.type": {
$ne: "FAILD"
}
}
},
{
$count: "withoutFailedInLastElemCount"
}
])

Answer 2

Unless it's crucial that the element be the last index, this should work for your case.
db.collection.find({
"targetsList.statusList.type": {
$in: [
"FAILD"
]
}
})
This will retrieve documents where the type value is FAILD. To invert this you can swap $in for $nin.
Updated playground here

Answer 3

Here's another way to do it with a leading monster "$match".
db.collection.aggregate([
{
"$match": {
"targetsList.target": "user",
"$expr": {
"$reduce": {
"input": "$targetsList",
"initialValue": false,
"in": {
"$or": [
"$$value",
{
"$ne": [
{
"$last": "$$this.statusList.type"
},
"FAILD"
]
}
]
}
}
}
}
},
{
"$count": "noFailedLastCount"
}
])
Try it on mongoplayground.net.