In MongoDB Not able to find sub-documents based on IDs - node.js

Question

I'm using MongoDb (as part of MongoJS) in Node. I using subdocuments and allocating IDs to the sub-docs also.
when I do a query based on the main documents it returns me the whole document, but when I try to find the sub-document based on its ID it do't return me any result. In mongoose I have declared a seperate schema for results field having its own ID.
It is to note that I am using arrays within arrays, for the result field.
Following is the console output of this scenario.
>db.tests.find({"_id":ObjectId("56563e92c8be03ec1a341374")}).pretty();
"_id" : ObjectId("56563e92c8be03ec1a341374"),
"test" : 2,
"startAt" : ISODate("2015-11-25T23:04:50Z"),
"endedAt" : ISODate("2015-11-25T23:04:50Z"),
"results" : [
{
"_id" : ObjectId("56563e92c8be03ec1a341375"),
"second" : [
{
"sec" : 50,
"avg" : 40.6,
"grt" : 1.2
}
]
}
],
>db.tests.find({"_id":ObjectId("56563e92c8be03ec1a341375")}).pretty();
>

Answer 1

You cannot search for subdocuments only by their ID in mongoDb. You have to always start from the main document i.e...search for the document that has an "results" array that contains the subdocument you are looking for:
db.test.find({ "results._id" : ObjectId("56563e92c8be03ec1a341375") });
if you want the output document to contain only the subdocument you were looking for (excluding other subdocuments it the array) you can use projection {"results.$":1}:
db.test.find({ "results._id" : ObjectId("56563e92c8be03ec1a341375") },{"results.$" : 1});
It will give you this output:
{
"_id": ObjectId("56563e92c8be03ec1a341374"),
"results": [{
"_id": ObjectId("56563e92c8be03ec1a341375"),
"second": [{
"sec": 50,
"avg": 40.6,
"grt": 1.2
}]
}]
}