MongoDB Aggregation - mongodb

Question

I have a the following collection
{ "data" :[
{ "country" :"USA", "state": "NJ", "County" : "Middlesex", "city" : "Edison", "population" :0923422 },
{ "country" :"USA", "state": "NJ", "County" : "Mercer", "city" : "Princeton", "population" :0923422 },
{ "country" :"USA", "state": "NY", "County" : "Middlesex", "city" : "Edison", "population" :234234 },
{ "country" :"USA", "state": "NY", "County" : "Ocean", "city" : "Albony", "population" :234324 },
{ "country" :"USA", "state": "PA", "County" : "Central", "city" : "Edison", "population" :0923422 },
{ "country" :"USA", "state": "NJ", "County" : "Middlesex", "city" : "Edison", "population" :23432 },
{ "country" :"USA", "state": "OH", "County" : "Middlesex", "city" : "Cincinatti", "population" :0923422 },
{ "country" :"USA", "state": "OH", "County" : "Middlesex", "city" : "Columbos", "population" :23432 } ]
}
looking to find the total population by Country, State, County and City with nested aggregation in mongodb.
Please help with query.

Answer 1

Query:-
db.collection.aggregate([
{$group:
{
_id : {"country" : "$country",
"state" : "$state",
"County" : "$County",
"city" : "$city"
},
"totalPopulationOfCity" : {$sum: "$population" }
}},
{$group:
{
_id : {"country" : "$_id.country",
"state" : "$_id.state",
"County" : "$_id.County"
},
"cities" : { $addToSet: {"city" : "$_id.city", "totalPopulationOfCity" : "$totalPopulationOfCity"} } ,
"totalPopulationOfCounty" : {$sum: "$totalPopulationOfCity" }
}},
{$group:
{
_id : {"country" : "$_id.country",
"state" : "$_id.state"
},
"counties" : {$addToSet: {"County": "$_id.County", "cities" : "$cities",
"totalPopulationOfCounty" : "$totalPopulationOfCounty"} } ,
"totalPopulationOfState" : {$sum: "$totalPopulationOfCounty" }
}},
{$group:
{
_id : {"country" : "$_id.country"
},
"states" : {$addToSet : {"state" : "$_id.state", "counties": "$counties", "totalPopulationOfState" : "$totalPopulationOfState"}},
"totalPopulationOfCountry" : {$sum: "$totalPopulationOfState" }
}},
]);
Output:-
/* 1 */
{
"_id" : {
"country" : "USA"
},
"states" : [
{
"state" : "NY",
"counties" : [
{
"County" : "Ocean",
"cities" : [
{
"city" : "Albony",
"totalPopulationOfCity" : 234324
}
],
"totalPopulationOfCounty" : 234324
},
{
"County" : "Middlesex",
"cities" : [
{
"city" : "Edison",
"totalPopulationOfCity" : 234234
}
],
"totalPopulationOfCounty" : 234234
}
],
"totalPopulationOfState" : 468558
},
{
"state" : "NJ",
"counties" : [
{
"County" : "Mercer",
"cities" : [
{
"city" : "Princeton",
"totalPopulationOfCity" : 923422
}
],
"totalPopulationOfCounty" : 923422
},
{
"County" : "Middlesex",
"cities" : [
{
"city" : "Edison",
"totalPopulationOfCity" : 946854
}
],
"totalPopulationOfCounty" : 946854
}
],
"totalPopulationOfState" : 1870276
},
{
"state" : "OH",
"counties" : [
{
"County" : "Middlesex",
"cities" : [
{
"city" : "Cincinatti",
"totalPopulationOfCity" : 923422
},
{
"city" : "Columbos",
"totalPopulationOfCity" : 23432
}
],
"totalPopulationOfCounty" : 946854
}
],
"totalPopulationOfState" : 946854
},
{
"state" : "PA",
"counties" : [
{
"County" : "Central",
"cities" : [
{
"city" : "Edison",
"totalPopulationOfCity" : 923422
}
],
"totalPopulationOfCounty" : 923422
}
],
"totalPopulationOfState" : 923422
}
],
"totalPopulationOfCountry" : 4209110
}
Verification using excel:-