$match and $unwind and $group
db.scores.aggregate( [
{ $match: { name: "bar" } },
{ $unwind: "$scores" },
{ $group: { _id: "$name", score: { $sum: "$scores" } } }
] )
{
"result": [
{
"_id": "bar",
"score": 18
}
],
"ok": 1
}