json - 获取 null，$sum 聚合 - Mongo

Question

谁能告诉我为什么在尝试按供应商 ID 汇总广告系列集合中的预算值时会得到 []？

这是我在数据库中的文档 - Campaign Collection

{
"_id" : ObjectId("5acf6ca923cdca5be18518cf"),
"vendorID" : ObjectId("5acf11eaeab7b52d8403ac17"),
"bookingID" : ObjectId("5acf6c9123cdca5be18518ce"),
"listingID" : ObjectId("5acf6c4d23cdca5be18518cd"),
"budget" : 200000,
"date" : "Thu Apr 12 2018 17:26:49 GMT+0300 (EAT)",
"__v" : 0
}

这是我正在使用的路由器 block

router.get('/campaign_sum/:vendorID', (req, res, next) => {
Campaign.aggregate([
    { $match : { "vendorID" : req.params.vendorID } },
    { 
        $group: {
            _id: null,
            total: { $sum: "$budget" }
        }
    }
], (err, value) => {
    res.json(value);
});
});

Answer 1

首先需要这样的 Mongoose :

var Mongoose = require('mongoose');

然后使用:

{ $match : { "vendorID" :  Mongoose.Types.ObjectId(req.params.vendorID)} }

而不是:

{ $match : { "vendorID" : req.params.vendorID } }