在同一个查询mongodb中获取最大值和计数

Question

在执行导出之前，我正在尝试验证数据。大多数人会首先验证数据，然后再将其添加到集合中，但在这种情况下，无法进行验证，因为需要在人员注册后分配网络和团队。所以，我要做的是检查序列中缺少的net#s。它应该去1，2，3，等等。我想我可以按事件分组，并使用$max来获得为该事件分配的最高的网。然后，我可以比较唯一的网数和$max数。如果他们是平等的，我们是好的。我想不出如何正确地进行查询。$max总是空的，或者没有出现。

样本数据：

{ "_id" : ObjectId("591c7e1710c42a02a1833fef"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 1, "team" : 1 },
{ "_id" : ObjectId("591c7e1710c42a02a1833fef"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 1, "team" : 2 },
{ "_id" : ObjectId("591c7e1710c42a02a1833fef"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 1, "team" : 3 },
{ "_id" : ObjectId("591c7e1710c42a02a1833fef"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 1, "team" : 4 }
{ "_id" : ObjectId("591e07186f335b497bef0f9a"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 3, "team" : 1 },
{ "_id" : ObjectId("591e07186f335b497bef0f9a"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 3, "team" : 2 },
{ "_id" : ObjectId("591e07186f335b497bef0f9a"), "event" : "Junior Girls 16s", "field" : "Main", "day" : "Friday", "division" : "Junior Girls", "level" : "16s", "group" : "nonpro", "numplayers" : 2, "price" : 50, "net" : 3, "team" : 3 }

我希望这些数据能够显示出来：

event                maxNet      count (count of unique event/net field combo)    
Junior Girls 16s     3           2

我尝试过的许多事情之一：

db.registrations.aggregate([
            {$match: {event: "Juniors Girls 16s"}},
            {$group: {_id: {event: "$event", net: "$net"}, count: {$sum:1}}},
            { $project: {event: "$event", count: {$sum: 1}, maxNet: {$max: "$_id.net"}}}
        ]);

有人能帮我弄清楚我怎么能修好它吗？

Answer 1

好吧，在上面你们这些出色的贡献者的帮助下，我能够让它发挥作用：

db.registrations.aggregate([          
     { "$match": searchParams },                
     { "$group": { "_id": { "event": "$event" },                         
                "netCount": {$addToSet: "$net"},                          
                "maxNet":{$max: "$net"}      }},
    {$project: {nets: {$size: "$netCount"},maxNet: "$maxNet"}}, 
    {$match: {nets: {$ne: "$maxNet"} }}       
])

这给出了事件，使用的唯一净编号的数目，以及用于该事件的最高净数。我试图使用最后一行：{$match: {nets: {$ne: "$maxNet"}}}只显示那些数字不相同的事件(我们跳过了一个网号，或者在两个不同的字段上使用了相同的一个)。不知道我做了什么使这个部分不工作，但它显示了我想要的结果，以最干净的方式。

Answer 2

如果我正确理解你的问题，这将给你你想要的：

db.registrations.aggregate([
    {$match: {event: 'Junior Girls 16s'}}, 
    {$group: {_id: {event: "$event", net: "$net"}, count: {$sum:1}}}, 
    {$project: {event: "$_id.event", count: "$count", maxNet: {$max: "$_id.net"}}}
]);