問題描述

我正在查詢一個集合并根據一個屬性對結果進行排序.有些文檔還沒有該屬性值，即 null.在排序和限制(asc 或 desc)之后，我想在結果末尾保留具有空值的文檔.Mongoose 中是否有一種簡單的方法可以使用單個查詢來做到這一點?如果沒有，我如何分別使用兩個查詢，因為我必須限制結果以及分頁?

I am querying a collection and sorting results based on a property. Some documents don't the that property value yet i.e. null. I want to keep the documents with null values at the end of the results after sorting and limiting (asc or desc). Is there a simple way in Mongoose to do that using a single query? If not, how can I use two queries separately since I have to limit the results as well for pagination?

var dealSchema = new Schema({

    // For Presentation Purposes Only
    dealId: { type: Number, index: true, unique: true },

    // BRAND Info
    brand: { type: ObjectId, ref: 'brand', index: true },
    brandUser: { type: ObjectId, ref: 'user', index: true, required: true },
    campaign: { type: ObjectId, ref: 'campaign', index: true },

    metrics: {
        totalCost: Number,
        totalValue: Number,
        roi: { type: Number, index: true },
        cpe: { type: Number, index: true }
    }

})

我想根據metrics.cpe"按升序排序，但希望 null 或 0 值位于列表末尾.示例:

I want to sort based on 'metrics.cpe' in ascending order, but want null or 0 values to be at the end of the list. Example:

[0.1, 0.4, 0.7, 1.5, 2.5, 0, 0, null, null]

示例文檔

{
  "_id": "590cdf29c102ae31208fa43a",
  "campaign": "587e6a880c844c6c2ea01563",
  "brand": "5a4cff5f8eaa1c26ca194acc",
  "brandUser": "57fd30cf0df04f1100153e07",
  "metrics": {
    "roi": 0,
    "cpe": 0,
    "totalValue": 0,
    "totalCost": 6000
  }
}

推薦答案

我不確定我要說的解決方案.我無法測試這一點，因為我現在沒有設置 mongo db，但我認為你可以使用 <collection>.aggregate 以及 $project 和 $sort 來實現這一點.

Am not sure about the solution am about to say. I cant test this out as I dont have a mongo db set right now, but I think that you can use <collection>.aggregate along with $project and $sort to achieve this.

示例代碼:

db.inventory.aggregate(
   [
      {
         $project: {
            item: 1,
            description: { $ifNull: [ "$amount", -1*(<mimimum value>)* ] }
         }
      },
      { 
         $sort : { 
           amount : (-1 or 1 depending on the order you want)
         }
      }
   ]
)

希望對你有幫助！！

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