How to find count of a key in one document using mongoDB? - mongodb

Question

I have following structure in my collection:
users:[
{
"name":"ABC",
"address":{
"city":"London",
"country":"UK",
}
},
{
"name":"XYZ",
"address":{
"city":"London",
"country":"UK",
}
},
{
"name":"PQR",
"address":{
"city":"NewYork",
"country":"US",
}
}
]
I want count of number of occurrences of 'city' key in 'address' and 'name' as a result.
I want to query above collection and want following output:
[{
"name":"ABC",
"city":"London",
"count":2
},{
"name":"XYZ",
"city":"London",
"count":2
}, {
"name":"PQR",
"city":"NewYork",
"count":1
}
]

Answer 1

I simulated your collection
{
"_id" : ObjectId("547c30ae371ea419f07b9550"),
"users" : [
{
"name" : "ABC",
"address" : {
"city" : "London",
"country" : "UK"
}
},
{
"name" : "XYZ",
"address" : {
"city" : "London",
"country" : "UK"
}
},
{
"name" : "PQR",
"address" : {
"city" : "NewYork",
"country" : "US"
}
}
]
}
And then I use aggregate framework
db.coll.aggregate([
{
$unwind:"$users"
},
{
$group:{
_id:"$users.address.city",
name:{$push:"$users.name"},
city:{$first:"$users.address.city"},
count:{$sum:1}
}
},{
$unwind:"$name"
},{
$project:{
_id:0,
"city":"$_id",
"name":1,
"city":1,
"count":1
}
}])
result:
{
"result" : [
{
"name" : "PQR",
"city" : "NewYork",
"count" : 1
},
{
"name" : "ABC",
"city" : "London",
"count" : 2
},
{
"name" : "XYZ",
"city" : "London",
"count" : 2
}
],
"ok" : 1
}
UPDATE AFTER QUESTION
I added a new Document
{
"_id" : ObjectId("547c394c371ea419f07b9551"),
"users" : [
{
"address" : {
"city" : "Livorno",
"country" : "LI"
}
},
{
"address" : {
"city" : "Livorno",
"country" : "LI"
}
},
{
"address" : {
"city" : "NewYork",
"country" : "US"
}
}
]
}
and new Query
db.coll.aggregate([
{
$unwind:"$users"
},
{
$group:{
_id:"$users.address.city",
"name": {
$push:{"$ifNull": ["$users.name","$_id"]}
},
city:{$first:"$users.address.city"},
count:{$sum:1}
}
},{
$unwind:"$name"
},{
$project:{
_id:0,
"city":"$_id",
"name":1,
"city":1,
"count":1
}
}])
Result:
{
"result" : [
{
"name" : "PQR",
"city" : "NewYork",
"count" : 2
},
{
"name" : ObjectId("547c394c371ea419f07b9551"),
"city" : "NewYork",
"count" : 2
},
{
"name" : ObjectId("547c394c371ea419f07b9551"),
"city" : "Livorno",
"count" : 2
},
{
"name" : ObjectId("547c394c371ea419f07b9551"),
"city" : "Livorno",
"count" : 2
},
{
"name" : "ABC",
"city" : "London",
"count" : 2
},
{
"name" : "XYZ",
"city" : "London",
"count" : 2
}
],
"ok" : 1
}