MongoDb

Question

给定以下集合：

留言合集

{ 
    "_id" : ObjectId("59f76fc3a8e87e411c22d0ac"),
    "OriginApp" : "App1", 
    "MsgGroupId" : "499", 
    "UserName" : "User1", 
    "Message" : "Test Message [Group ID: 499]"
}
{ 
    "_id" : ObjectId("59f76fc3a8e87e411c22d0ad"),
    "OriginApp" : "App1", 
    "MsgGroupId" : "499", 
    "UserName" : "User2", 
    "Message" : "Test Message [Group ID: 499]"
}
{ 
    "_id" : ObjectId("59f76fc3a8e87e411c22d0af"),
    "OriginApp" : "App1", 
    "MsgGroupId" : "499", 
    "UserName" : "User3", 
    "Message" : "Test Message [Group ID: 499]"
}

消息事件集合

{ 
    "_id" : ObjectId("59f772d1d22ea83b249d19c2"),
    "Event" : "Send", 
    "Msg" : {
        "UserName" : "User1", 
        "Metadata" : {
            "OriginApp" : "App1", 
            "MessageId" : "59f76fc3a8e87e411c22d0ac"
        }, 
    }, 
    "TimeStamp" : "2017-10-30T18:20:17Z"
}
{ 
    "_id" : ObjectId("59f772d1d22ea83b249d19c2"), 
    "Event" : "Open", 
    "Msg" : {
        "UserName" : "User1", 
        "Metadata" : {
            "OriginApp" : "App1", 
            "MessageId" : "59f76fc3a8e87e411c22d0ac"
        }, 
    }, 
    "TimeStamp" : "2017-10-30T18:30:16Z"
}
{ 
    "_id" : ObjectId("59f772d1d22ea83b249d19c2"), 
    "Event" : "Click", 
    "Msg" : {
        "UserName" : "User1", 
        "Metadata" : {
            "OriginApp" : "App1", 
            "MessageId" : "59f76fc3a8e87e411c22d0ac"
        }, 
    }, 
    "TimeStamp" : "2017-10-30T18:38:57Z"
}

我想要 return 如下所示的投影：

{ 
    "MessageId" : "59f76fc3a8e87e411c22d0ac" 
    "EventId" : "59f772d1d22ea83b249d19c2", 
    "Event" : "Send", 
    "UserName" : "User1", 
    "OriginApp" : "App1", 
    "TimeStamp" : "2017-10-30T18:20:17Z"
}
{ 
    "MessageId" : "59f76fc3a8e87e411c22d0ac" 
    "EventId" : "59f772d1d22ea83b249d19c2", 
    "Event" : "Open", 
    "UserName" : "User1", 
    "OriginApp" : "App1", 
    "TimeStamp" : "2017-10-30T18:30:16Z"
}
{ 
    "MessageId" : "59f76fc3a8e87e411c22d0ac" 
    "EventId" : "59f772d1d22ea83b249d19c2", 
    "Event" : "Click", 
    "UserName" : "User1", 
    "OriginApp" : "App1", 
    "TimeStamp" : "2017-10-30T18:38:57Z"
}

我运行立即遇到问题，因为 MsgEvent.Msg.Metadata.MessageId 是一个字符串，而 Message._id 是一个 ObjectId。不可能将 create MsgEvent.Msg.Metadata.MessageId 作为 ObjectId，因为它由外部应用程序 return 编辑到服务，就像 json 一样简单。

有没有办法使用不同的运算符或某种类型的聚合来实现所需的结果？

--更新--

鉴于 MongoDb 不允许在查询中进行数据转换（这是原始问题的一部分），我现在通过提供一个附加属性（作为字符串的 Guid）解决了这个问题：

留言合集

{ 
    "_id" : ObjectId("59f76fc3a8e87e411c22d0ac"),
    "GuidString" : "d273a5dd-7291-432f-a9ab-8bad7343a1a4",
    "OriginApp" : "App1", 
    "MsgGroupId" : "499", 
    "UserName" : "User1", 
    "Message" : "Test Message [Group ID: 499]"
}

消息事件集合

{ 
    "_id" : ObjectId("59f772d1d22ea83b249d19c2"),
    "Event" : "Send", 
    "Msg" : {
        "UserName" : "User1", 
        "Metadata" : {
            "OriginApp" : "App1", 
            "MessageId" : "59f76fc3a8e87e411c22d0ac",
            GuidString" : "d273a5dd-7291-432f-a9ab-8bad7343a1a4"
        }, 
    }, 
    "TimeStamp" : "2017-10-30T18:20:17Z"
}

等...

以下聚合将 return 预期结果：

db.MessageEvent.aggregate(
[
{ $match : { "Msg.Metadata.GuidString" : "d273a5dd-7291-432f-a9ab-8bad7343a1a4" } },
{ $unwind: "$Msg" },
{
   $lookup: {
    "from": "GuidString",
    "localField": "ChannelSenderId",
    "foreignField": "GuidString",
    "as": "messages"
  } 
}
]);

Answer 1

合并多个集合或对数据进行任何重塑（例如分组、取消分组（unwind））的唯一方法是使用聚合框架（推荐）或旧的 map reduce 框架（不推荐）。

具体来说，在聚合时，您可以选择各种聚合步骤，包括 $lookup。

通过简要查看您的数据，您需要聚合 MessageEvent 集合和 Message 集合中的查找数据（因为 ID 从 MessageEvent 指向 Message 对象，反之亦然）。

您有 $project、$group 阶段可以帮助您重塑数据。

MongoDb - "Join" 合集

MongoDb - "Join" Collections

join

distinct

aggregation