How to distinct (count) value when value is nested in array? - node.js

Question

I have a data sample something like this:
"diagnostics" : {
"_ID" : "554bbf7b761e06f02fef3561",
"tests" : [
{
"_id" : "59d678064e4645ec562a37e2",
"name" : "RBC",
},
{
"_id" : "59d678064e4645ec562a37e1",
"name" : "Calcium",
}
]
}
I want to get all distinct _ID and count of all test groups in with there names
which is something like this:
"_ID" : "554bbf7b761e06f02fef3561"{ {"name" : "Calcium", count :(count of Calcium)},{"name" : "RBC", count :(count of RBC)}
Thing to keep in mind are tests is inside diagnostics and contain any number of $name field it can be two or one or any number of times and I want individual count of each distinct name .
db.collection('transactions').aggregate([
{ $unwind : '$diagnostics.tests' },
{ $group : {
_id: {
"Test_Name" : '$diagnostics.tests.name',
"ID" : '$diagnostics._id'
},
test_count: { $sum: 1 }
}
}
])
and I am getting result something like this
[
{
"_id": {
"Test_Name": "Fasting Blood Sugar",
"ID": "554bbf7b761e06f02fef3561"
},
"test_count": 76
},
{
"_id": {
"Test_Name": "Fasting Blood Sugar",
"ID": "566726c35dc18d13242fffcc"
},
"test_count": 1
},
{
"_id": {
"Test_Name": "CBC - 7 Part",
"ID": "566726c35dc18d13242fffcc"
},
"test_count": 1
},
{
"_id": {
"Test_Name": "RBC",
"ID": "554bbf7b761e06f02fef3561"
},
"test_count": 1
},
{
"_id": {
"Test_Name": "Fasting Blood Sugar",
"ID": "5a2c9edfe0d0ec71aef1e526"
},
"test_count": 6
},
{
"_id": {
"Test_Name": "Calcium",
"ID": "554bbf7b761e06f02fef3561"
},
"test_count": 77
}
]
Can anybody help me with the query?

Answer 1

You need to use mulitple $group stages here.
First $unwind the tests and $group it by "name" and then resize it to original and lastly then $group by "diagnostics_ID" and for the tests count you can check the $size of the "tests" array.
db.collection.aggregate([
{ "$unwind": "$diagnostics.tests" },
{ "$group": {
"_id": {
"_id": "$diagnostics.tests.name",
"diagnosticID": "$diagnostics._ID"
},
"count": { "$sum": 1 }
}},
{ "$group": {
"_id": {
"_ID": "$_id.diagnosticID"
},
"tests": {
"$push": {
"name": "$_id._id",
"count": "$count"
}
}
}},
{ "$project": {
"diagnostics._ID": "$_id._ID",
"diagnostics.tests": "$tests",
"_id": 0,
"testCount": { "$size": "$tests" }
}}
])
Code snippet