javascript - 如何在 mongodb 中使用 $nin 运算符从集合中获取文档

Question

我有一个像这样的用户架构

const userSchema= new mongoose.Schema({

  Username:{
      type:String,
      trim:true,
      required:true
  },
  email:{
    type:String,
    trim:true,
    required:true
},
hashed_password:{
    type:String,
    trim:true,
    required:true
},
salt:String,
created:{
type:Date,
default:Date.now,
},
updated:Date,
photo:{
data:Buffer,
contentType:String
},

about:{
 type:String   
},

following:[{type:ObjectId,ref:"User",}],

followers:[{type:ObjectId,ref:"User"}]
})

当我运行查询时

User.find({$_id:{$nin:following}} , (err, users) => {
    if (err) {
      return res.status(400).json({
        error: err,
      });
    }
    res.json(users)
  //  let data=users

  //  console.log(following.length,"following")

  //  console.log(newuser)

  }).select("Username")


};
the following variable is an array of objects like this

[{"_id":"5e9c2c7aa9f4bc46e88c7635","用户名":" bat 侠"},{"正​​在关注":[],"关注者":[],"_id":"5ead159d3b41d7061ce639fe","已创建":"2020-05-13T19:37:17.161Z"}]

after running the query i get an error:
 "errmsg": "unknown top level operator: $_id",
        "code": 2,
        "codeName": "BadValue",

如何在查询中正确输入字段

Answer 1

从_id中删除$，就像运算符mongodb一样，将其识别为运算符，例如($match等) ，但是没有这样的运算符，所以它会抛出错误

User.find({_id:{$nin:following}} , (err, users) => {
    if (err) {
      return res.status(400).json({
        error: err,
      });
    }
    res.json(users)
  //  let data=users

  //  console.log(following.length,"following")

  //  console.log(newuser)

  }).select("Username")


};