使用 MongoDB 时获取组 _id 的数组

Question

我需要在 mongoDB 中使用 group 计算一些记录，但在我的情况下，_id 数组即将到来。我在下面解释我的查询。

let query = {
      $group: {
             _id:  "$Products.ProductName",
             dispatchcount: { $sum: 1 },
             totalDispatchValue: {$sum:"$TotalAmount.TotalPayment"},
             totalDiscountValue: {$sum: "$TotalDiscount.TotalDiscountAmount"}
      }
}
pipeLine.push(query);
const orders = await dispatchOrdersCol.aggregate(pipeLine);

实际输出：

[
            {
                "_id": [
                    "Unisex Navy Blue Belt"
                ],
                "dispatchcount": 1,
                "totalDispatchValue": 27922,
                "totalDiscountValue": 4084
            },
            {
                "_id": [
                    "Writing Ruled Note Book",
                    "Physics Record Book",
                    "Chemistry Record Book",
                    "Computer Science Record Book"
                ],
                "dispatchcount": 1,
                "totalDispatchValue": 2190,
                "totalDiscountValue": 0
            },
            {
                "_id": [
                    "PU2-Physics Part-1 Text Book",
                    "PU2-Physics Part-2 Text Book",
                    "PU2-Mathematics Part - 1 Text Book",
                    "PU2-Chemistry Part - 1 Text Book",
                    "PU2-English Text Book",
                    "PU2-Mathematics Part - 2 Text Book",
                    "PU2-Chemistry Part - 2 Text Book",
                    "PU2-English Work Book",
                    "PU2-TEXT BOOK",
                    "PU2-Sanskrit Text Book",
                    "Boys White & Blue Striped Half Shirt",
                    "Boys Navy Blue Regular Fit Trousers",
                    "Illume Calf-length Cotton Black Socks  "
                ],
                "dispatchcount": 1,
                "totalDispatchValue": 4131,
                "totalDiscountValue": 150
            },
            {
                "_id": [
                    "PU2-TEXT BOOK"
                ],
                "dispatchcount": 1,
                "totalDispatchValue": 1679,
                "totalDiscountValue": 0
            }
        ]

这里对于_id 键有多个值，其中一些值还在下一条记录中重复。

猫鼬模型：

const Model = new Schema({
        DispatchId: { type: Number, required: true },
        OrderNumber: { type: String, unique: true, required: true },
        OrderStatus: { type: String },
        OrderType: { type: String },        
        DispatchPriority: { type: String },

        Comments: { type: Array },
        Products: { type: Array },

        Customer: { type: Object },     
        TotalDiscount: { type: Object },
        TotalShipping: { type: Object },
        TotalCoupon: { type: Object },
        TotalAmount: { type: Object },
        PaymentDetails: { type: Object },
        ClientDetails: { type: Object },

        DispatchCreatedAt: { type: String },
        DispatchUpdatedAt: { type: String },

        IsActive: { type: Boolean }
    }, 
    {
        timestamps: { 
            createdAt: 'CreatedAt', 
            updatedAt: 'UpdatedAt' 
        },
        collection: DISPATCH_ORDERS_COLLECTION
    }
);

这里我需要根据产品名称计算total Payment and total Discount。但在我的情况下，一个产品也在两个记录中出现两次。

Answer 1

在您的文档中Products 是一个数组，（可能是一个带有ProductName 字段的对象数组）当您执行"$Products.ProductName" 时，它会给您一个产品名称数组。所以$group 必须对其中包含完全相同元素的数组进行分组（即使两个数组之间的一个元素不匹配也会在小组赛阶段被视为_id 上的两个值）。所以你需要在 $group 阶段之前对 Products 数组执行 $unwind ：

查询不正确：

db.collection.aggregate([
  /** You don't need this addFields stage, just given to test, you can remove `$group` stage & check the `products` field value */
  {
    $addFields: {
      products: "$products.productName"
    }
  },
  {
    $group: {
      _id: "$products" // arrays
    }
  }
])

测试： mongoplayground

正确查询：

db.collection.aggregate([
  {
    $unwind: "$products"
  },
  {
    $addFields: {
      products: "$products.productName"
    }
  },
  {
    $group: {
      _id: "$products" // Single value
    }
  }
])

测试： mongoplayground

参考： $unwind