带有条件的 MongoDB 查找答案

【问题标题】：MongoDB Lookup with Conditions带有条件的 MongoDB 查找
【发布时间】：2020-02-27 14:25:04
【问题描述】：

很抱歉，我确定这是一个新手问题，但经过几个讲台后，我完全不知道如何解决这个问题。

我目前有两个系列，一个是orders，另一个是offers。报价基本上是订单的报价报价（由_id<->orderId链接）。

订单集合示例：

{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : true, 
    "updated" : ISODate("2017-06-02T08:20:47.772+0000"), 
    "created" : ISODate("2017-06-02T08:10:51.401+0000"), 
    "name" : "Sicherungsbolzen",
    "state" : "active"
}
{ 
    "_id" : ObjectId("59311ee2a0ea6500113df5d8"), 
    "deleted" : false, 
    "updated" : ISODate("2017-06-02T08:16:34.911+0000"), 
    "created" : ISODate("2017-06-02T08:16:34.911+0000"), 
    "name" : "Mitnehmerstein SK50 ",
    "state" : "active"
}

报价集合示例：

{ 
    "_id" : ObjectId("59311ee2a0ea6500113df5d8"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T13:18:34.872+0000"), 
    "created" : ISODate("2019-11-08T06:54:14.072+0000"), 
    "orderId" : ObjectId("5db6c679d8499800286ff64a"), 
    "proposal" : {
        "price" : NumberInt(19800), 
        "currency" : "CUR51", 
        "deliveryDate" : NumberInt(21), 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T10:11:48.112+0000"), 
    "created" : ISODate("2019-10-29T11:31:05.980+0000"), 
    "orderId" : ObjectId("5db74034d849980028701a95"), 
    "proposal" : {
        "price" : 31.78, 
        "currency" : "CUR48", 
        "deliveryDate" : NumberInt(1), 
        "files" : [

        ]
    }
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T08:37:04.354+0000"), 
    "created" : ISODate("2019-11-08T08:37:04.354+0000"), 
    "orderId" : ObjectId("5db80b84ed142100263a5088"), 
    "proposal" : {
        "price" : NumberInt(2345), 
        "deliveryDate" : NumberInt(18), 
        "currency" : "CUR48", 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-15T14:32:15.958+0000"), 
    "created" : ISODate("2019-11-06T14:42:23.492+0000"), 
    "orderId" : ObjectId("5dc03382751ecc002899e1fa"), 
    "proposal" : {
        "price" : NumberInt(86400), 
        "currency" : "CUR48", 
        "deliveryDate" : NumberInt(90), 
        "files" : [

        ]
    }
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-22T23:10:07.056+0000"), 
    "created" : ISODate("2019-11-06T20:09:20.706+0000"), 
    "orderId" : ObjectId("5dc03382751ecc002899e1fa"), 
    "proposal" : {
        "price" : NumberInt(57419), 
        "currency" : "CUR48", 
        "deliveryDate" : NumberInt(27), 
        "files" : [

        ]
    }
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T08:52:18.910+0000"), 
    "created" : ISODate("2019-11-08T08:52:18.910+0000"), 
    "orderId" : ObjectId("5dc05c0a751ecc00289a0187"), 
    "proposal" : {
        "price" : NumberInt(9900), 
        "deliveryDate" : NumberInt(35), 
        "currency" : "CUR48", 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311d8ba0ea6500113df5d6"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T09:39:12.383+0000"), 
    "created" : ISODate("2019-11-08T09:39:12.383+0000"), 
    "orderId" : ObjectId("5dc47fb10a1f7c00262763e3"), 
    "proposal" : {
        "price" : NumberInt(79), 
        "deliveryDate" : NumberInt(7), 
        "currency" : "CUR48", 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311ee2a0ea6500113df5d8"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T09:45:41.392+0000"), 
    "created" : ISODate("2019-11-08T09:45:41.392+0000"), 
    "orderId" : ObjectId("5dc480ab751ecc00289b32c7"), 
    "proposal" : {
        "price" : NumberInt(240), 
        "deliveryDate" : NumberInt(7), 
        "currency" : "CUR48", 
        "message" : "Hi Alex, I saw you put several RFQs in the platform,attached quotation for reference.If you have any question,please contact me at engineer07@top-rp.cn. Looking forward to your feedback.By the way,may I know your email?\n\nRebecca", 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311ee2a0ea6500113df5d8"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T09:43:29.928+0000"), 
    "created" : ISODate("2019-11-08T09:43:29.928+0000"), 
    "orderId" : ObjectId("5dc482430a1f7c00262763e6"), 
    "proposal" : {
        "price" : NumberInt(390), 
        "deliveryDate" : NumberInt(7), 
        "currency" : "CUR48", 
        "message" : "Hi Alex, I saw you put several RFQs in the platform,attached quotation for reference.If you have any question,please contact me at engineer07@top-rp.cn. Looking forward to your feedback.By the way,may I know your email?\n\nRebecca", 
        "files" : [

        ]
    }, 
}
{ 
    "_id" : ObjectId("59311ee2a0ea6500113df5d8"), 
    "deleted" : false, 
    "updated" : ISODate("2019-11-08T06:56:15.346+0000"), 
    "created" : ISODate("2019-11-08T06:56:15.346+0000"), 
    "orderId" : ObjectId("5dc4843b0a1f7c00262763ed"), 
    "proposal" : {
        "price" : NumberInt(3), 
        "deliveryDate" : NumberInt(7), 
        "currency" : "CUR48", 
        "files" : [

        ]
    }, 
}

我有一个主要目标： 导出将显示每个报价的“平均”价格的 Excel。也就是说，如果一个订单收到 3 个报价（20、30、40），它将是：OrderID, 30（30 是 20、30、40 的平均值）。

在这种情况下，有 2 个订单（59311d8ba0ea6500113df5d6 和 59311ee2a0ea6500113df5d8），它必须显示：

ORDERID, AVERAGE OF PRICE

59311ee2a0ea6500113df5d8, 99 (average all the proposal.price for each quote of this order)
59311d8ba0ea6500113df5d6, 129 (average all the proposal.price for each quote of this order)

任何提示、技巧、帮助？

提前致谢

【问题讨论】：

请提供两种情况下的样本数据和预期结果
being 90 the average of 20, 30, 40 是错字还是您的意思是 sum？
这确实是一个错字对不起。现在更正它。

标签： mongodb aggregation-framework lookup

【解决方案1】：

这看起来像是新的$lookup 的工作

db.Orders.aggregate([
 {$project:{_id:1}),
 {$lookup: {
     from: "Quotes",
     let: {order:"$_id"},
     pipeline: [
        {$match: {$expr: {$eq:["$orderId","$$order"]}}},
        {$group: {_id:null, average:{$avg:"$proposal.price"}}}
     ],
     as: "quotes"
 }}
])

这应该返回类似

的文档

{_id: ObjectId("..."),
quotes:[{_id:null, average:xxx}]}

【讨论】：