db.collection is not a function when using MongoClient v3.0

Question

I have been trying W3schools tutorial on nodeJS with MongoDB.

When I try to implement this example in a nodeJS environment and invoke the function with an AJAX call, I got the error below:

TypeError: db.collection is not a function
    at c:\Users\user\Desktop\Web Project\WebService.JS:79:14
    at args.push (c:\Users\user\node_modules\mongodb\lib\utils.js:431:72)
    at c:\Users\user\node_modules\mongodb\lib\mongo_client.js:254:5
    at connectCallback (c:\Users\user\node_modules\mongodb\lib\mongo_client.js:933:5)
    at c:\Users\user\node_modules\mongodb\lib\mongo_client.js:794:11
    at _combinedTickCallback (internal/process/next_tick.js:73:7)
    at process._tickCallback (internal/process/next_tick.js:104:9)

Please find below my implemented code:

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/mytestingdb";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  db.collection("customers").findOne({}, function(err, result) {
    if (err) throw err;
    console.log(result.name);
    db.close();
  });
});

Note that the error occurs whenever the execution hits:

db.collection("customers").findOne({}, function(err, result) {}

Also, note (in case it matters) that I have installed the latest MongoDB package for node JS (npm install mongodb), and the MongoDB version is MongoDB Enterprise 3.4.4, with MongoDB Node.js driver v3.0.0-rc0.

Answer 1

I encountered the same thing. In package.json, change mongodb line to "mongodb": "^2.2.33". You will need to uninstall mongodb npm by removing MongoDB Driver/ node_modules or etc , then install npm to install this version.

This resolved the issue for me. Seems to be a bug or docs need to be updated.

Answer 2

For people on version 3.0 of the MongoDB native NodeJS driver:

(This is applicable to people with "mongodb": "^3.0.0-rc0", or a later version in package.json, that want to keep using the latest version.)

In version 2.x of the MongoDB native NodeJS driver you would get the database object as an argument to the connect callback:

MongoClient.connect('mongodb://localhost:27017/mytestingdb', (err, db) => {
  // Database returned
});

According to the changelog for 3.0 you now get a client object containing the database object instead:

MongoClient.connect('mongodb://localhost:27017', (err, client) => {
  // Client returned
  var db = client.db('mytestingdb');
});

The close() method has also been moved to the client. The code in the question can therefore be translated to:

MongoClient.connect('mongodb://localhost', function (err, client) {
  if (err) throw err;

  var db = client.db('mytestingdb');

  db.collection('customers').findOne({}, function (findErr, result) {
    if (findErr) throw findErr;
    console.log(result.name);
    client.close();
  });
}); 

Answer 3

For those that want to continue using version ^3.0.1 be aware of the changes to how you use the MongoClient.connect() method. The callback doesn't return db instead it returns client, against which there is a function called db(dbname) that you must invoke to get the db instance you are looking for.

const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');

// Connection URL
const url = 'mongodb://localhost:27017';

// Database Name
const dbName = 'myproject';

// Use connect method to connect to the server
MongoClient.connect(url, function(err, client) {
  assert.equal(null, err);
  console.log("Connected successfully to server");

  const db = client.db(dbName);

  client.close();
});

Answer 4

MongoClient.connect(url (err, client) => {
    if(err) throw err;

    let database = client.db('databaseName');

    database.collection('name').find()
    .toArray((err, results) => {
        if(err) throw err;

        results.forEach((value)=>{
            console.log(value.name);
        });
    })
})

The only problem with your code is that you are accessing the object that's holding the database handler. You must access the database directly (see database variable above). This code will return your database in an array and then it loops through it and logs the name for everyone in the database.

Answer 5

Piggy backing on @MikkaS answer for Mongo Client v3.x, I just needed the async / await format, which looks slightly modified as this:

const myFunc = async () => {

     // Prepping here...


    // Connect
    let client = await MongoClient.connect('mongodb://localhost');
    let db = await client.db();

    // Run the query
    let cursor = await db.collection('customers').find({});

    // Do whatever you want on the result.
}

Answer 6

I did a little experimenting to see if I could keep the database name as part of the url. I prefer the promise syntax but it should still work for the callback syntax. Notice below that client.db() is called without passing any parameters.

MongoClient.connect(
    'mongodb://localhost:27017/mytestingdb', 
    { useNewUrlParser: true}
)
.then(client => {

    // The database name is part of the url.  client.db() seems 
    // to know that and works even without a parameter that 
    // relays the db name.
    let db = client.db(); 

    console.log('the current database is: ' + db.s.databaseName);
    // client.close() if you want to

})
.catch(err => console.log(err));

My package.json lists monbodb ^3.2.5.

The 'useNewUrlParser' option is not required if you're willing to deal with a deprecation warning. But it is wise to use at this point until version 4 comes out where presumably the new driver will be the default and you won't need the option anymore.

Answer 7

I solved it easily via running these codes:

 npm uninstall mongodb --save

 npm install [email protected] --save

Happy Coding!

Answer 8

If someone is still trying how to resolve this error, I have done this like below.

const MongoClient = require('mongodb').MongoClient;
// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'mytestingdb';

const retrieveCustomers = (db, callback)=>{
    // Get the customers collection
    const collection = db.collection('customers');
    // Find some customers
    collection.find({}).toArray((err, customers) =>{
        if(err) throw err;
      console.log("Found the following records");
      console.log(customers)
      callback(customers);
    });
}

const retrieveCustomer = (db, callback)=>{
    // Get the customers collection
    const collection = db.collection('customers');
    // Find some customers
    collection.find({'name': 'mahendra'}).toArray((err, customers) =>{
        if(err) throw err;
      console.log("Found the following records");
      console.log(customers)
      callback(customers);
    });
}

const insertCustomers = (db, callback)=> {
    // Get the customers collection
    const collection = db.collection('customers');
    const dataArray = [{name : 'mahendra'}, {name :'divit'}, {name : 'aryan'} ];
    // Insert some customers
    collection.insertMany(dataArray, (err, result)=> {
        if(err) throw err;
        console.log("Inserted 3 customers into the collection");
        callback(result);
    });
}

// Use connect method to connect to the server
MongoClient.connect(url,{ useUnifiedTopology: true }, (err, client) => {
  console.log("Connected successfully to server");
  const db = client.db(dbName);
  insertCustomers(db, ()=> {
    retrieveCustomers(db, ()=> {
        retrieveCustomer(db, ()=> {
            client.close();
        });
    });
  });
});

Answer 9

I have MongoDB shell version v3.6.4, below code use mongoclient, It's good for me:

var MongoClient = require('mongodb').MongoClient,
assert = require('assert');
var url = 'mongodb://localhost:27017/video';
MongoClient.connect(url,{ useNewUrlParser: true }, function(err, client) 
{
assert.equal(null, err);
console.log("Successfully connected to server");
var db = client.db('video');
// Find some documents in our collection
db.collection('movies').find({}).toArray(function(err, docs) {
// Print the documents returned
docs.forEach(function(doc) {
console.log(doc.title);
});
// Close the DB
client.close();
});
// Declare success
console.log("Called find()");
 });

Answer 10

It used to work with the older versions of MongoDb client ~ 2.2.33

Option 1: So you can either use the older version

npm uninstall mongodb --save

npm install [email protected] --save

Option 2: Keep using the newer version (3.0 and above) and modify the code a little bit.

let MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://localhost:27017', function(err, client){
  if(err) throw err;
  let db = client.db('myTestingDb');
  db.collection('customers').find().toArray(function(err, result){
    if(err) throw err;
    console.log(result);
    client.close();
    });
 });

Answer 11

MongoDB queries return a cursor to an array stored in memory. To access that array's result you must call .toArray() at the end of the query.

  db.collection("customers").find({}).toArray() 

Answer 12

Late answer but maybe someone will need it in future

we can create async function which one will return our collection and db instances

const dBInstances = async () => {
  const collection = await db
    .then((client) => {
      const db = client.db();
      const collection = db.collection("AGGREGATION");
      return { collection: collection, db: db };
    })
    .catch((err) => {
      console.log(`Data base instances error ${err}`);
    });

  return collection;
};

and after we can use result of execution dBInstances() by this way i used JS destructurisation in example below

const test = async (req, res) => {
  const { collection, db } = await dBInstances();
  console.log(collection);
  console.log(db);
};

now we have separated access to our db and collection.