Mongo DB group records and return selected fields - mongodb

Question

I want to group the documents on the basis of a specific value. Also I need the selected keys in return.
Here is my document:
{
title: "Add 1",
userId: 1,
description: "this is add 1",
location: {
city: "Newyork",
address: "Street 1, Flat # 40"
},
createdAt: "2015-10-20",
title: "Add 2",
userId: 1,
description: "this is add 2",
location: {
city: "Paris",
address: "Street 2, Flat # 80"
},
createdAt: "2015-10-22",
title: "Add 3",
userId: 1,
description: "this is add 3",
location: {
city: "Newyork",
address: "Street 5, Flat # 58"
},
createdAt: "2015-10-23"
}
I want to group the documents by location.city. Also I need only title and location in return.
What should be the query for above scenario?
I have tried this query:
Adds.aggregate([
{ $match: { userId: params.userId } },
{ $group: { _id: "$location.city" } },
]);
The above query only returns location.city, I want complete object of location & title.

Answer 1

Assuming that your data actually looks like this:
[
{
title: "Add 1",
description: "this is add 1",
location: {
city: "Newyork",
address: "Street 1, Flat # 40"
},
createdAt: "2015-10-20",
},
{
title: "Add 2",
description: "this is add 2",
location: {
city: "Paris",
address: "Street 2, Flat # 80"
},
createdAt: "2015-10-22",
},
{
title: "Add 3",
description: "this is add 3",
location: {
city: "Newyork",
address: "Street 5, Flat # 58"
},
createdAt: "2015-10-23"
}
]
You could use an aggregate query such as:
db.adds.aggregate([
{ $group :
{
_id : "$location.city",
data : { $push : { "title" : "$title", "location" : "$location" } }
}
}
]);

Answer 2

userId is missing in your documents, if your collection looks like this your aggregate function is correct.
{
"title": "Add 1",
"userId": 1,
"description": "this is add 1",
"location": {
"city": "Newyork",
"address": "Street 1, Flat # 40"
},
"createdAt": "2015-10-20"
},
{
"title": "Add 2",
"userId": 2
"description": "this is add 2",
"location": {
"city": "Paris",
"address": "Street 2, Flat # 80"
},
"createdAt": "2015-10-22"
},
{
"title": "Add 3",
"userId": 1,
"description": "this is add 3",
"location": {
"city": "Newyork",
"address": "Street 5, Flat # 58"
},
"createdAt": "2015-10-23"
}
Test using Mongodb's console
db.Adds.aggregate([
{ $match: { userId: 1 } },
{ $group: { _id: "$location.city" } }
]);
Adding title to your results
db.Adds.aggregate([
{ $match: { userId: 1 } },
{
$group: {
_id: "$location.city",
title: {$push: "$title"}
}
}
]);