node.js - Mongodb 查找 + 使用 mongoose 进行分组

Question

我有两个不同的 Mongoose 集合，如下:

{ "_id" : 1, "countryId" : 1, "price" : 12, "quantity" : 24 }
{ "_id" : 2, "countryId" : 2, "price" : 20, "quantity" : 1 }
{ "_id" : 3  }
{ "_id" : 4, "countryId" : 1, "price" : 12, "quantity" : 24 }



{ "_id" : 1, "id" : 1, description: "Colombia"}
{ "_id" : 3, "id" : 2, description: "Mexic" }

我正在尝试聚合它们，以便得到如下结果:

{"country":"Colombia","total":48}
{"country":"Mexic","total":1}

我尝试了很多东西，但总是失败，这是我正在开发的最后一个版本(我已经更改了数据，但你明白了):

Model.aggregate([
      {
      $lookup:
        {
          from: "countryList",
          localField: "countryId",
          foreignField: "id",
          as: "country"
        },
       {
       $project: {
                    quantity:1, country:{$country:"$countryList.description"}
                 }
       },{
         $group:{
                 { _id : null, qtyCountry: { $sum: "$quantity" } }
         }
       }
   }],function (err, result) {
        if (err) {
            console.log(err);
        } else {
            console.log(result)
        }
    }
);

这可能吗？

Answer 1

是的，这是可能的。您可以尝试以下聚合管道。

var pipeline = [
                    {"$match":{"countryId":{"$exists":true}}},
                    {"$group" : {"_id":"$countryId", "quantity":{"$sum":"$quantity"}}}, 
                    {"$lookup":{"from":"countryList","localField":"_id", "foreignField":"id","as":"country"}}, 
                    {"$unwind":"$country"}, 
                    {"$project": {"country":"$country.description", "total":"$quantity", _id:0}}
                ]

示例输出:

{ "country" : "Mexic", "total" : 1 }
{ "country" : "Colombia", "total" : 48 }