无法使用NodeJ检查MongoDB上是否存在字段

Question

I am using NodeJs and MongoDb as a backend service from my android app.I am checking if Phone field exists in my database. My problem is everytime I check for the field it sends response field exists even if Phone field is not present in document.

Here is my code:

const express = require('express');
const bodyParser = require('body-parser');
const env = require('dotenv').config();
const router = express.Router();
const MongoClient = require('mongodb').MongoClient;

var dburl = process.env.URL;

router.use(bodyParser.json());
router.use(bodyParser.urlencoded({extended:true}));

router.post('/checkPhone',(req,res) => {

        var data = req.body.uId;

MongoClient.connect(dburl,{useNewUrlParser:true},(err,client) => {

              if(err){

                console.log("Error:" +err);
              }
              else{

                var collect = client.db('Bookbudi_db').collection('Users');

                collect.find({_id:data,Phone:{$exists:true}},(err,doc) => {

                             if(err){

                                console.log("Error:" +err);
                             }
                             if(doc){

                                res.send("Exist");
                             }
                             else{

                                res.send("Doesn't exist");
                             }

                });

              }

     });  

 });

module.exports = router;

Someone please let me know what I am doing wrong in above code. Any help would be appreciated.

THANKS

Answer 1

if { $exists:true } returns the document - it means that the field is there.

It is possible that your schema defines this field and initiates it w/ null - note that $exists will still return those fields.

References: $exists