MongoDb projection on array of objects, Get matched object only [duplicate] - arrays

Question

This question already has answers here:
Retrieve only the queried element in an object array in MongoDB collection
(18 answers)
Closed 4 years ago.
I have mongo document like this
{
"_id": "5b14679e592baa493e0bc208",
"productCode": "ABC",
"corridors": [
{
"countryNameEn": "Sweden",
"countryNameFr": "Suède",
"countryCode": "SE",
"currencyNameEn": "Swedish Krona",
"currencyNameFr": "Couronne suédoise",
"currencyCode": "SEK",
"corridorLimit": "abc"
},
{
"countryNameEn": "USA",
"countryNameFr": "Suède",
"countryCode": "US",
"currencyNameEn": "USA",
"currencyNameFr": "Couronne suédoise",
"currencyCode": "USD",
"corridorLimit": "abc"
}
]
},
{
"_id": "5b14679e592baa493e0bc208",
"productCode": "XYZ",
"corridors": [
{
"countryNameEn": "Sweden",
"countryNameFr": "Suède",
"countryCode": "SE",
"currencyNameEn": "Swedish Krona",
"currencyNameFr": "Couronne suédoise",
"currencyCode": "SEK",
"corridorLimit": "abc"
},
{
"countryNameEn": "USA",
"countryNameFr": "Suède",
"countryCode": "US",
"currencyNameEn": "USA",
"currencyNameFr": "Couronne suédoise",
"currencyCode": "USD",
"corridorLimit": "abc"
}
]
}
I want to find document whose productCode is ABC and currencyCode is USD in corridors array. How can I return only the matching object from corridors array like only only object that has USD currencyCode should come in result and not all array.
I tried running this query { productCode: 'ABC', corridors: { $elemMatch: { currencyCode: "USD"}}}. But it gives me the whole array and not the only matched element.

Answer 1

I don't think you can use $elemMatch in $project. Check this
Try the following query:
db.collection.aggregate([
{
$match : {"productCode" : "ABC"}
},
{
$unwind : "$corridors"
},
{
$match : { "corridors.currencyCode" : "USD"}
},
{
$group : {
_id : "$productCode",
corridors : {$addToSet : "$corridors"}
}
}]);
Outputs:
{
"_id" : "ABC",
"corridors" : [
{
"countryNameEn" : "USA",
"countryNameFr" : "Suède",
"countryCode" : "US",
"currencyNameEn" : "USA",
"currencyNameFr" : "Couronne suédoise",
"currencyCode" : "USD",
"corridorLimit" : "abc"
}
]
}
In the result you'll have _id instead of productCode. If you still want productCode, you can just include $project in the end.
Hope this helps!