node.js - Mongoose 聚合查询 $match 中的 $max

Question

我是 Mongoose 的新手，在尝试使用聚合查询获取一些数据时遇到问题。

我的拍卖模式的一部分是:

  "_id" : ObjectId("56c58be1faaa402c0d4ae66f"),
        "auction_name" : "Auction2",
        "auction_start_datetime" : ISODate("2016-02-18T09:30:00.000Z"),
        "auction_end_datetime" : ISODate("2016-02-22T09:00:00.000Z"),
        "auction_status" : "active",
        "auction_series" : "GA-06-C",
        "auction_reserve_price" : 1000,
        "auction_increment_amount" : 200,
        "fancy_numbers" : [ 
            {
                "number_end_datetime" : ISODate("2016-02-22T09:00:00.000Z"),
                "number_start_datetime" : ISODate("2016-02-18T09:30:00.000Z"),
                "increment_amount" : 200,
                "reserve_price" : 1000,
                "number" : 5000,
                "_id" : ObjectId("56c58da3faaa402c0d4ae739"),
                "bid_users" : [ 
                    {
                        "user_id" : "56c416a599ad7c9c1611b90b",
                        "bid_amount" : 7200,
                        "bid_time" : ISODate("2016-02-18T11:58:53.025Z"),
                        "user_name" : "amit@mailinator.com",
                        "_id" : ObjectId("56c5aec4acebf3b4061a645e")
                    }, 
                    {
                        "user_id" : "56c172dc302a2c90179c7fd1",
                        "bid_amount" : 15400,
                        "bid_time" : ISODate("2016-02-19T10:38:43.506Z"),
                        "user_name" : "rbidder@mailinator.com",
                        "_id" : ObjectId("56c5afe0d2baef7020ede1b6")
                    }, 
                    {
                        "user_id" : "56c477afb27a7ed824c54427",
                        "bid_amount" : 2800,
                        "bid_time" : ISODate("2016-02-18T11:56:58.830Z"),
                        "user_name" : "bidder2@mailinator.com",
                        "_id" : ObjectId("56c5b18a78c3fb340a8c6d75")
                    }, 
                    {
                        "user_id" : "56c5b17378c3fb340a8c6d73",
                        "bid_amount" : 5600,
                        "bid_time" : ISODate("2016-02-18T11:58:34.616Z"),
                        "user_name" : "bidder3@mailinator.com",
                        "_id" : ObjectId("56c5b1d778c3fb340a8c6d78")
                    }
                ]
            }
]

这里，fancy_number是拍卖集合下的一个数组，bid_users是每个fancy_number下的一个数组。

我有user_id，我想查询并只获取出价最高者的bid_user记录。

例如:

There are 3 users bidded 200,300,400 respectively, I want to get the record (i.e number and amount) only if this particular user bid is 400 (highest). where ill be passing the user_id

我编写的聚合查询是:

var ObjectID = require('mongodb').ObjectID;
tempId = new ObjectID(req.body.aId);

auctionModel.aggregate({$match: {'_id': tempId}},
                        {$unwind: '$fancy_numbers'},
                        {$unwind:"$fancy_numbers.bid_users"},
                        {$group: {'_id':"$fancy_numbers.number" , maxBid: { $max: '$fancy_numbers.bid_users.bid_amount'}}},  
    function(err, bidData){
        if(err){
            console.log('Error :' + err);
        }
        else if(bidData) {
            console.log(bidData);
        }
     });

不知何故，这个查询不起作用，它只给出最高出价和数量的记录。仅当他是出价最高者时我才想要记录。

Answer 1

如果我没猜错，请尝试通过$sort和$limit检索最高出价者，如下

auctionModel.aggregate(.aggregate([
                            {$match: {'_id': '123'}}, 
                            {$unwind: '$fancy_numbers'}, 
                            {$unwind: '$fancy_numbers.bid_users'}, 
                            {$sort: {bid_amount: 1}}, 
                            {$limit: 1}]);