Node.js Mongo DB查找查询未按预期工作

Question

Please help me find error in my code

const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:27017';
var a = "2018";
var b = "December";
var c = "12";
var temp = "17";

var query = `{'${b}.${c}.temp':'${temp}'}`;
console.log(query);

MongoClient.connect(url,{ useNewUrlParser: true },(err, client) => {
    if (err){
      return console.log('Unable to login to Mongo DB');
    }
    const db = client.db('test'); 
 db.collection('updateTest').find(query).toArray()
.then((result) =>{
    if(err){
        return console.log(err);
    }if(result.length > 0){
        console.log(JSON.stringify(result));
    }else{
        console.log(JSON.stringify({Error:"Cannot find request"}));
    }
});
client.close();
});

When I use condition directly in the find({"December.12.temp":temp}) it works fine

When I assign condition to a variable and use it in find(query) it works fine.

var query = {"December.12.temp":temp};

But when I assign a value from input by user the query doesn't work as expected instead works as if no condition was specified.

var query = `{'${b}.${c}.temp':'${temp}'}`;

Answer 1

When you use backticks (``), query variable becomes a string, after all the JavaScript embedded in it has executed (ie using the values of b and c). You actually require the query variable to be an object, not a string. Thus it fails. Have a look at this doc Ps: I ended up answering in comments too.

Answer 2

var a = "2018";
var b = "December";
var c = "12";
var temp = "17";
var query = {};

var value = '${b}.${c}.temp';

query[value] = temp;

db.collection('updateTest').find(query).toArray()
.then((result) =>{
    if(err){
       return console.log(err);
    }if(result.length > 0){
        console.log(JSON.stringify(result));
    }else{
        console.log(JSON.stringify({Error:"Cannot find request"}));
    }

}