Aggregating an array of values in MongoDB - mongodb

Question

I have an array of values I want to group by the id of, and get the sum of all the values. Currently I'm trying:
db.entries.aggregate(
[
{ $match: {"user": "John" } },
{ "$unwind": '$games'},
{ $group: {
"_id": "$games.id",
"score": { "$sum": "$games.score"} }},
])
The data looks like:
{
"user":"john",
"games":[
{
"id":123,
"score":123
}
]
},
{
"user":"john",
"games":[
{
"id":123,
"score":123
}
]
},
{
"user":"john",
"games":[
{
"id":256,
"score":256
}
]
}
In this example, for "John" I would like to get the total of all the unique game scores. I should get (123 + 256) in this example.
However, right now I'm getting the sum of individual games, not all of them as a total.

Answer 1

I have here:
> db.entries.find();
{ "_id" : ObjectId("56a9610cca390d7e14a54486"), "user" : "john", "games" : [ { "id" : 123, "score" : 123 } ] }
{ "_id" : ObjectId("56a9610cca390d7e14a54487"), "user" : "john", "games" : [ { "id" : 123, "score" : 123 } ] }
{ "_id" : ObjectId("56a9610cca390d7e14a54488"), "user" : "john", "games" : [ { "id" : 256, "score" : 256 } ] }
> db.entries.aggregate([ {$match: {user: "john"}}, {$unwind: "$games"}, {$group: {_id: "$games.id", score: {$sum: "$games.score"}}} ]);
{ "_id" : 256, "score" : 256 }
{ "_id" : 123, "score" : 246 }
What’s the problem?