如果查找id位于嵌入式文档mongodb中，如何高效地实现连接？

考虑一个场景，

用户

可以订阅许多

频道

，而

频道

属于

出版商

基本上有三个实体

1：用户

2：频道

3：出版商

下面是以db格式保存的示例数据：

{
  "_id" : ObjectId("5a7428b7408437d7155bbde9"),
  "name" : "some subscriber who is a user ",
    "channelSubscription" : {
      "5a740c88408437d7155bbdca" : {
      "_id" : "5a740c88408437d7155bbdca",
      "channel_name" : "1st channel",
      "channelBelongsTo" : "publisher._id" // replace id with publisher details
   },

    "5a7411dc408437d7155bbdcb" : {
       "_id" : "5a7411dc408437d7155bbdcb",
       "channel_name" : "2nd channel",
       "channelBelongsTo" : "someOtherPublisher._id" // replace id with publisher details
     }
   }
}

---

我如何在此处进行连接以获取发布者的详细信息，以便

channelBelongsTo

可以拥有发布者的详细信息。您需要在此处使用聚合框架以获得所需的结果。聚合管道最初应该创建一个新字段，该字段是hashmap的键/值对数组，可以使用管道步骤和$objectToArray操作符。因此，您的第一个管道步骤是：

db.user.aggregate([
    {
       "$addFields": {
           "subscriptions": { "$objectToArray": "$channelSubscription" }
       } 
    }
])

产生

{
    "_id" : ObjectId("5a7428b7408437d7155bbde9"),
    "name" : "some subscriber who is a user ",
    "channelSubscription" : {
        "5a740c88408437d7155bbdca" : {
            "_id" : "5a740c88408437d7155bbdca",
            "channel_name" : "1st channel",
            "channelBelongsTo" : "1"
        },
        "5a7411dc408437d7155bbdcb" : {
            "_id" : "5a7411dc408437d7155bbdcb",
            "channel_name" : "2nd channel",
            "channelBelongsTo" : "2"
        }
    },
    "subscriptions" : [ 
        {
            "k" : "5a740c88408437d7155bbdca",
            "v" : {
                "_id" : "5a740c88408437d7155bbdca",
                "channel_name" : "1st channel",
                "channelBelongsTo" : "1"
            }
        }, 
        {
            "k" : "5a7411dc408437d7155bbdcb",
            "v" : {
                "_id" : "5a7411dc408437d7155bbdcb",
                "channel_name" : "2nd channel",
                "channelBelongsTo" : "2"
            }
        }
    ]
}

---

对于加入，您需要附加管道步骤，该步骤获取发布者的详细信息，如下所示：

db.user.aggregate([
    {
       "$addFields": {
           "subscriptions": { "$objectToArray": "$channelSubscription" }
       } 
    },
    {
        "$lookup": {
            "from": "publisher",
            "localField": "subscriptions.v.channelBelongsTo",
            "foreignField": "_id",
            "as": "publishers"
        }
    }
])

---

没用的出版商现在是一片空白，我错了，

“localField”：“subscriptions.v.channelBelongsTo”

存储为

字符串，而不是
对象ID
谢谢！！