{
    "_id": {
        "$oid": "5abcbee7ff1e4849b8f642b5"
    },
    "name": "test1",
    "email": "[email protected]",
    "username": "test1",
    "password": "$2a$10$/Y6Gns8OPsp8eudVBrfUx.clwNwixAmeqhVzBYKUyNuoGcR3XQP8e",
    "joindate": "29/03/2018 11:24",
    "lastdailybonus": "28/03/2018 11:24",
    "profileimgurl": "img.jpg",
    "referralUrl": "r1xk1rq5g",
    "referredBy":"syiqyb9cz",
    "referredUsers": [
        {
            "id": {
                "$oid": "5abcbf29ff1e4849b8f642b6"
            },
            "coins": 50
        },
        {
            "id": {
                "$oid": "5abcbf9b9a3ca4425489777e"
            },
            "coins": 76
        }
    ],
    "completedMissions": [],
    "coinsEarned":1500,
    "__v": 2
}

回答如下：

尝试这个：

db.sample.aggregate([
{
    $addFields: {
        totalCoins: {
            $reduce: {
                input: "$referredUsers",
                initialValue: 0,
                in: { $add : ["$$value", "$$this.coins"] }
            }
          }
        }
     },
     {$addFields:{totalCoins:{$add:["$totalCoins","$coinsEarned"]}}},
     {$out: "sample"}
])