mongodb聚合查找返回集合中的每个项

我想使用mongodb和aggregate查找两个集合，这是我的查询：

db.getCollection('buddies').aggregate([
{
     $lookup:
       {
         from: "users",
         localField: "ObjectId(userId)",
         foreignField: "ObjectId(_id)",
         as: "user_buddy"
       }
  }
])

问题是我使用userId来聚合它

users

collection和

buddies

collection是1对1

我希望它将添加由buddies.userId和users匹配的

user\u buddy

属性。\u id，但我得到的是不同的：

/* 1 */
{
    "_id" : ObjectId("5b3a2fca0fe843093879b5bc"),
    "isVerified" : false,
    "isActivated" : false,
    "createdAt" : ISODate("2018-07-02T13:59:05.273Z"),
    "userId" : "5b2deca18966a405412d1266",
    "phone" : "+6239109301",
    "photo" : "https://cloudinary.com",
    "idCardType" : "KTP",
    "idNumber" : "19901390193019",
    "updatedAt" : ISODate("2018-07-02T13:59:05.273Z"),
    "__v" : 0,
    "user_buddy" : [ 
        {
            "_id" : ObjectId("5b2dec013efecd0514a50561"),
            "createdAt" : ISODate("2018-06-23T06:43:11.092Z"),
            "username" : "lalaland",
            "email" : "lalaland@gmail.com",
            "fullname" : "Lala Princess",
            "nickname" : "lala",
            "password" : "$2a$08$LUs3fW/YPzkQeHvqH7QvTOr5H8RgqTGVvldFcUHFcfBGoRs.jn0hS",
            "updatedAt" : ISODate("2018-06-23T06:43:11.092Z"),
            "__v" : 0
        }, 
        {
            "_id" : ObjectId("5b2deca18966a405412d1266"),
            "createdAt" : ISODate("2018-06-23T06:45:48.578Z"),
            "username" : "yozawiratama",
            "email" : "yoza@yahoo.com",
            "fullname" : "Yoza Extra",
            "nickname" : "Yoza",
            "password" : "$2a$08$uZ/G61qtqdlSgSz.Qzt/i.ufiUBoPq7H8ViVwlJ1pA9SUZYUp34sO",
            "updatedAt" : ISODate("2018-06-23T06:45:48.578Z"),
            "__v" : 0
        }
    ]
} 

正如您所看到的，好友的userid是5b2deca18966a405412d1266，但在

user\u buddy

中返回两个文档，其中一个文档具有不同的

\u id

我希望它能匹配

buddies.userId

和

users.\u id

---

如何解决这个问题？

localField

和

foreignField

是字段名

应该是

db.getCollection('buddies').aggregate([
{
     $lookup:
       {
         from: "users",
         localField: "userId",
         foreignField: "_id",
         as: "user_buddy"
       }
  }
])

没有“ObjectId”

ObjectId应位于文档本身中：

{
    "_id" : ObjectId("5b3a2fca0fe843093879b5bc"),
    "isVerified" : false,
    "isActivated" : false,
    "createdAt" : ISODate("2018-07-02T13:59:05.273Z"),
    "userId" : ObjectId("5b2deca18966a405412d1266")
    ....

---

您的

用户ID

是字符串。。。将其转换为猫鼬对象你是说当我插入它时？