Get matched embedded document(s) from array - mongodb

Question

I've got a lot of documents using the following structure in MongoDB:
{
"_id" : ObjectId("..."),
"plant" : "XY_4711",
"hour" : 1473321600,
"units" : [
{
"_id" : ObjectId("..."),
"unit_id" : 10951,
"values" : [
{
"quarter" : 1473321600,
"value" : 395,
},
{
"quarter" : 1473322500,
"value" : 402,
},
{
"quarter" : 1473323400,
"value" : 406,
},
{
"quarter" : 1473324300,
"value" : 410,
}
]
}
]
}
Now I need to find all embedded document values where the quarter is between some given timestamps (eg: { $gte: 1473324300, $lte: 1473328800 }).
I've only got the unit_id and the quarter timestamp from/to for filtering the documents. And I only need the quarter and value grouped and ordered by unit.
I'm new in MongoDB and read something about find() and aggregate(). But I don't know how to do it. MongoDB 3.0 is installed on the server.
Finally I've got it:
I simply have to take apart each array, filtering out the things I don't need and put it back together:
db.collection.aggregate([
{$match : {$and : [{"units.values.quarter" : {$gte : 1473324300}}, {"units.values.quarter" : {$lte : 1473328800 }}]}},
{$unwind: "$units"},
{$unwind: "$units.values"},
{$match : {$and : [{"units.values.quarter" : {$gte : 1473324300}}, {"units.values.quarter" : {$lte : 1473328800 }}]}},
{$project: {"units": {values: {quarter: 1, "value": 1}, unit_id: 1}}},
{$group: {"_id": "$units.unit_id", "quarter_values": {$push: "$units.values"}}} ,
{$sort: {"_id": 1}}
])
Will give:
{
"_id" : 10951,
"quarter_values" : [
{
"quarter" : 1473324300,
"value" : 410
},
{
"quarter" : 1473325200,
"value" : 412
},
{
"quarter" : 1473326100,
"value" : 412
},
{
"quarter" : 1473327000,
"value" : 411
},
{
"quarter" : 1473327900,
"value" : 408
},
{
"quarter" : 1473328800,
"value" : 403
}
]
}
See: Return only matched sub-document elements within a nested array for a detailed description!
I think I have to switch to $map or $filter in the future. Thanks to notionquest for supporting my questions :)

Answer 1

Please see the sample query below. I didn't exactly get your grouping requirement. However, with this sample query you should be able to change and get your desired output.
db.collection.aggregate([
{$unwind : {path : "$units"}},
{$match : {$and : [{"units.values.quarter" : {$gte : 1473324300}}, {"units.values.quarter" : {$lte : 1473328800 }}]}},
{$project : {"units" : {values : {quarter : 1, "value" : 1}, unit_id : 1}}},
{$group : { _id : "$units.unit_id", quarter_values : { $push :{ quarter : "$units.values.quarter", value : "$units.values.value"}}}},
{$sort : {_id : 1 }}
]);
Sample output:-
{
"_id" : 10951,
"quarter_values" : [
{
"quarter" : [
1473321600,
1473322500,
1473323400,
1473324300
],
"value" : [
395,
402,
406,
410
]
}
]
}