node.js - 如何获取特定数字字段与所有匹配记录的总和

Question

我将 Mongoose 与node.js一起使用，我有交易模型和发票模型。我想获取所有具有特定发票 ID 的记录。我使用此查询来获取发票的匹配交易。

Transaction.find({invoice_id: invoiceId})

我正在以这种形式获取记录

[
  {
    "_id": "5795e3f4f4a0fb8c1dff20ad",
    "description": "This is a transcation",
    "invoice_id": "5795db00bfa9d366194a454d",
    "amount": 50
  },
  {
    "_id": "5795e3faf4a0fb8c1dff20ae",
    "description": "This is a transcation",
    "invoice_id": "5795db00bfa9d366194a454d",
    "amount": 100
  }
]

但问题是我还想通过交易数组的每个对象中的“金额”字段值之和来获取totalAmount。我想要的结果是

[
  {
    "_id": "5795e3f4f4a0fb8c1dff20ad",
    "description": "This is a transcation",
    "invoice_id": "5795db00bfa9d366194a454d",
    "amount": 50
  },
  {
    "_id": "5795e3faf4a0fb8c1dff20ae",
    "description": "This is a transcation",
    "invoice_id": "5795db00bfa9d366194a454d",
    "amount": 100
  },
{
totalAmount: 150
}
]

我使用 $sum 聚合函数，但我不知道我的问题将如何解决。

Answer 1

为此目的，您应该使用聚合和 $group

  Transaction.aggregate([{
                $group: {
                   _id:{ invoice_id:"$invoice_id"
                    },
                    count: {
                        $sum: 1
                    },
                  totalAmount: { $sum: "$amount" },
                }
            }]).exec()