Need help in querying mongodb - arrays

Question

I have a a few documents that have the following structure. See attached image.
document structure
Each document includes an array of 'FileMeta' objects and each FileMeta object includes an array of 'StatusHistory' objects. I'm trying to get only the FileMetas that contain StatusCode equal to 4 and that the TimeStamp is greater than a certain datetime.
Tried the following query but it only returns the first FileMeta element of each document.
db.getCollection('Collection').find({'ExternalParams.RequestingApplication':'aaa.bbb'},
{ "FileMeta": { $elemMatch: { "StatusHistory":{ $elemMatch:{ "StatusCode": 4, "TimeStamp": { $gt: ISODate("2020-06-28T11:02:26.542Z")} } } } }} )
What am I doing wrong?
here is the document structure:
{
"_id" : ObjectId("5ef84e2ec08abf38b0043ab4"),
"FileMeta" : [
{
"StatusHistory" : [
{
"StatusCode" : 0,
"StatusDesc" : "New File",
"TimeStamp" : ISODate("2020-06-28T11:00:46.286Z")
},
{
"StatusCode" : 2,
"StatusDesc" : "stby",
"TimeStamp" : ISODate("2020-06-28T11:02:20.400Z")
},
{
"StatusCode" : 4,
"StatusDesc" : "success",
"TimeStamp" : ISODate("2020-06-28T11:02:26.937Z")
}
]
},
{
"StatusHistory" : [
{
"StatusCode" : 0,
"StatusDesc" : "New File",
"TimeStamp" : ISODate("2020-06-28T11:00:46.286Z")
},
{
"StatusCode" : 2,
"StatusDesc" : "stby",
"TimeStamp" : ISODate("2020-06-28T11:02:20.617Z")
},
{
"StatusCode" : 4,
"StatusDesc" : "success",
"TimeStamp" : ISODate("2020-06-28T11:02:26.542Z")
}
]
}
],
}
I want to return only the FileMeta objects that include a StatusHistory that match the following conditions: StatusCode = 4 and TimeStamp > SomeDateTime

Answer 1

Sorry for the delay, mate, I've been quite busy lately. Hope you already solved your problem. Anyway, I think that I found the solution.
As you can see on this link, the example shows that by default the $elemMatch operator returns the whole array in case of match on any element.
For instance, consider the following collection:
{ _id: 1, results: [ { product: "abc", score: 10 }, { product: "xyz", score: 5 } ] }
{ _id: 2, results: [ { product: "abc", score: 8 }, { product: "xyz", score: 7 } ] }
{ _id: 3, results: [ { product: "abc", score: 7 }, { product: "xyz", score: 8 } ] }
If you do the following query, for example:
db.survey.find(
{ results: { $elemMatch: { product: "xyz", score: { $gte: 8 } } } }
)
The output will be:
{ "_id" : 3, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "xyz", "score" : 8 } ] }
Not:
{ "_id" : 3, "results" : [{ "product" : "xyz", "score" : 8 }]}
That said, if you want to return only the document in the array that matches the specified query, you must use the db.collection.aggregate() function with the $unwind and $match operator.
The query below shall give you what you want.
Query:
db.collection.aggregate([
{"$unwind" : "$FileMeta"},
{"$unwind" : "$FileMeta.StatusHistory"},
{
"$match" : {
"FileMeta.StatusHistory.StatusCode" : 4,
"FileMeta.StatusHistory.TimeStamp" : {"$gte" : ISODate("2020-06-28T11:02:26.937Z")}
}
}
]).pretty()
Result:
{
"_id" : ObjectId("5ef84e2ec08abf38b0043ab4"),
"FileMeta" : {
"StatusHistory" : {
"StatusCode" : 4,
"StatusDesc" : "success",
"TimeStamp" : ISODate("2020-06-28T11:02:26.937Z")
}
}
}
One last tip. Consider changing your modeling to something that looks like the unwinded document, and remember that one document should be equivalent to one row in a normal relational database. So avoid storing information that should be on "several rows" on a single document.
Useful links:
The $elemMatch operator.
The $unwind operator.