Mongo DB - Group By and Having Implementation - mongodb

Question

I'm trying to write a Mongo DB query where I do the following,
JSON list - Representing documents in my collection,
Industry[]:
{
"_id" : ObjectId("57aa6058be0c853c8cee34cd"),
"options": {
"paramList" : [
{
"name" : "industryCategory",
"value" : "Travel",
"mandatory" : true
},
{
"name" : "someOtherThing",
"value" : "dontMind",
"mandatory" : true
}
]
}
"mostRecent" : true
},
{
"_id" : ObjectId("57aa6058be0c853c8cee34cd"),
"options": {
"paramList" : [
{
"name" : "industryCategory",
"value" : "Dining",
"mandatory" : true
},
{
"name" : "someOtherThing",
"value" : "dontMind",
"mandatory" : true
}
]
}
"mostRecent" : true
},
{
"_id" : ObjectId("57aa6058be0c853c8cee34cd"),
"options": {
"paramList" : [
{
"name" : "industryCategory",
"value" : "Travel",
"mandatory" : true
},
{
"name" : "someOtherThing",
"value" : "dontMind",
"mandatory" : true
}
]
}
"mostRecent" : true
}
I'm trying to group and get a count of values for those paramList - values where name is industryCategory. Essentially, the output I am looking for is something like this,
Travel: 2
Dining: 1
I'm trying to do the following,
Industry is the name of the collection,
db.Industry.aggregate (
[
{$match: {mostRecent: true}},
{$group: {
_id: '$options.paramList.value',
count: {$sum: 1}
}},
{$match: {'options.paramList.name': 'industryCategory'}}
])
I'm getting an empty result. Please suggest what I can do

Answer 1

Well, I didn't have anyone answering. But, in the meanwhile I managed to figure it out myself. Posting the answer below,
aggregate (
[
{"$match": {mostRecent: true}},
{"$unwind" : "$options.paramList"},
{"$group" :
{
_id: "$options.paramList.value",
count: {$sum : 1}
}
}
]
Essentially, use unwind wherever you have to iterate over arrays (a list of sub-documents). This has been a productive learning, at least for me.