Mongodb 将 _id 字段从 String 加入到 ObjectId [英] Mongodb Join on _id field from String to ObjectId

问题描述

我有两个收藏

1. 用户

   <代码>{"_id" : ObjectId("584aac38686860d502929b8b"),姓名":约翰"}

2. 角色

   <代码>{"_id" : ObjectId("584aaca6686860d502929b8d"),"角色": "管理员",用户 ID":584aac38686860d502929b8b"}

我想根据 userId(在 role 集合中) - _id(在 user> 收藏).

我尝试了以下查询:

db.role.aggregate({$查找":{"来自": "用户","localField": "userId","foreignField": "_id",作为":输出"}})

只要我将 userId 存储为 ObjectId，这就会给我预期的结果.当我的 userId 是一个字符串时，没有结果.Ps:我试过了

<块引用>

外来字段:'_id'.valueOf()

和

<块引用>

外来字段:'_id'.toString()

.但是没有运气匹配/加入基于 ObjectId 字符串字段.

任何帮助将不胜感激.

解决方案

从 MongoDB 3.4 开始，这是不可能的.此功能已被请求，但尚未实现.以下是相应的门票:

• SERVER-22781:允许在 ObjectId (_id.str) 和字符串
• SERVER-24947:需要布尔值的类型转换机制，ISODates、ObjectID

现在您必须将 userId 存储为 ObjectId

<小时>

编辑

以前的票在 MongoDB 4.0 中已修复.您现在可以使用以下查询实现此目的:

db.user.aggregate([{$项目":{_ID": {"$toString": "$_id"}}},{$查找":{"from": "角色","localField": "_id","foreignField": "userId",作为":角色"}}])

结果:

<预><代码>[{"_id": "584aac38686860d502929b8b",角色": [{"_id": ObjectId("584aaca6686860d502929b8d"),"角色": "管理员",用户 ID":584aac38686860d502929b8b"}]}]

在线试用:mongoplayground.net/p/JoLPVIb1OLS

I have two collections

1. User

   {
      "_id" : ObjectId("584aac38686860d502929b8b"),
      "name" : "John"
   }
   

2. Role

   {
      "_id" : ObjectId("584aaca6686860d502929b8d"),
      "role" : "Admin",
      "userId" : "584aac38686860d502929b8b"  
   }
   

I want to join these collection based on the userId (in role collection) - _id ( in user collection).

I tried the below query:

db.role.aggregate({
  "$lookup": {
    "from": "user",
    "localField": "userId",
    "foreignField": "_id",
    "as": "output"
  }
})

This gives me expected results as long as i store userId as a ObjectId. When my userId is a string there are no results. Ps: I tried

foreignField: '_id'.valueOf()

and

foreignField: '_id'.toString()

. But no luck to match/join based on a ObjectId-string fields.

Any help will be appreciated.

解决方案

This is not possible as of MongoDB 3.4. This feature has already been requested, but hasn't been implemented yet. Here are the corresponding tickets:

• SERVER-22781: Allow $lookup between ObjectId (_id.str) and string
• SERVER-24947: Need a type conversion mechanism for booleans, ISODates, ObjectID

For now you'll have to store userId as ObjectId

---

EDIT

The previous tickets were fixed in MongoDB 4.0. You can now achieve this with the folowing query:

db.user.aggregate([
  {
    "$project": {
      "_id": {
        "$toString": "$_id"
      }
    }
  },
  {
    "$lookup": {
      "from": "role",
      "localField": "_id",
      "foreignField": "userId",
      "as": "role"
    }
  }
])

result:

[
  {
    "_id": "584aac38686860d502929b8b",
    "role": [
      {
        "_id": ObjectId("584aaca6686860d502929b8d"),
        "role": "Admin",
        "userId": "584aac38686860d502929b8b"
      }
    ]
  }
]

try it online: mongoplayground.net/p/JoLPVIb1OLS

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