MongoDB - Project specific element from array (big data) - mongodb

Question

I got a big array with data in the following format:
{
"application": "myapp",
"buildSystem": {
"counter": 2361.1,
"hostname": "host.com",
"jobName": "job_name",
"label": "2361",
"systemType": "sys"
},
"creationTime": 1517420374748,
"id": "123",
"stack": "OTHER",
"testStatus": "PASSED",
"testSuites": [
{
"errors": 0,
"failures": 0,
"hostname": "some_host",
"properties": [
{
"name": "some_name",
"value": "UnicodeLittle"
},
<MANY MORE PROPERTIES>,
{
"name": "sun",
"value": ""
}
],
"skipped": 0,
"systemError": "",
"systemOut": "",
"testCases": [
{
"classname": "IdTest",
"name": "has correct representation",
"status": "PASSED",
"time": "0.001"
},
<MANY MORE TEST CASES>,
{
"classname": "IdTest",
"name": "normalized values",
"status": "PASSED",
"time": "0.001"
}
],
"tests": 8,
"time": 0.005,
"timestamp": "2018-01-31T17:35:15",
"title": "IdTest"
}
<MANY MORE TEST SUITES >,
]}
Where I can distinct three main structures with big data: TestSuites, Properties, and TestCases. My task is to sum all times from each TestSuite so that I can get the total duration of the test. Since the properties and TestCases are huge, the query cannot complete. I would like to select only the "time" value from TestSuites, but it kind of conflicts with the "time" of TestCases in my query:
db.my_tests.find(
{
application: application,
creationTime:{
$gte: start_date.valueOf(),
$lte: end_date.valueOf()
}
},
{
application: 1,
creationTime: 1,
buildSystem: 1,
"testSuites.time": 1,
_id:1
}
)
Is it possible to project only the "time" properties from TestSuites without loading the whole schema? I already tried testSuites: 1, testSuites.$.time: 1 without success. Please notice that TestSuites is an array of one element with a dictionary.
I already checked this similar post without success:
Mongodb update the specific element from subarray

Answer 1

Following code prints duration of each TestSuite:
query = db.my_collection.aggregate(
[
{$match: {
application: application,
creationTime:{
$gte: start_date.valueOf(),
$lte: end_date.valueOf()
}
}
},
{ $project :
{ duration: { $sum: "$testSuites.time"}}
}
]
).forEach(function(doc)
{
print(doc._id)
print(doc.duration)
}
)

Answer 2

Is it possible to project only the "time" properties from TestSuites
without loading the whole schema? I already tried testSuites: 1,
testSuites.$.time
Answering to your problem of prejecting only the time property of the testSuites document you can simply try projecting it with "testSuites.time" : 1 (you need to add the quotes for the dot notation property references).
My task is to sum all times from each TestSuite so that I can get the
total duration of the test. Since the properties and TestCases are
huge, the query cannot complete
As for your task, i suggest you try out the mongodb's aggregation framework for your calculations documents tranformations. The aggregations framework option {allowDiskUse : true} will also help you if you are proccessing "large" documents.