node.js db.collection.insertOne - MongoError: E11000 duplicate key error collection: _id_ dup

Question

In node.js, from one javascript loop, I am trying to insert one json object into one mongodb collection but getting duplicate key error on _id column.

{ MongoError: E11000 duplicate key error collection: app.Tab2017index: id dup key: { : ObjectId('5cbc813227b2ca2864b3c66a') }

Here is my part of my javascript code, which is causing error.

const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');
const url = 'mongodb://localhost:27017';
const dbName = 'app';    
var jsonData = {};

  MongoClient.connect(url,{useNewUrlParser: true}, function(err, client) {
    assert.equal(null, err);
    if(err) { return console.dir(err); }
    const db = client.db(dbName);
    const collection = db.collection('Tab2017')

    for (var i = 0; i < 5; i++) {        
            jsonData["test"] = "line";                          
                console.log('LINE_'+i+'- '+JSON.stringify(jsonData));
                collection.insertOne(jsonData, (err, result) => {                       
                    if(err) { console.dir(err); }                           
                    console.log('mongodb insert done');             
                })              
        }     
  })

Above code is showing error on console,

D:\app\server\routes>node linmon.route-backup3.js
LINE_0- {"test":"line"}
LINE_1- {"test":"line","_id":"5cbc813227b2ca2864b3c66a"}
LINE_2- {"test":"line","_id":"5cbc813227b2ca2864b3c66a"}
LINE_3- {"test":"line","_id":"5cbc813227b2ca2864b3c66a"}
LINE_4- {"test":"line","_id":"5cbc813227b2ca2864b3c66a"}
mongodb insert done
-------------------------------------------
{ MongoError: E11000 duplicate key error collection: app.Tab2017 index: _id_ dup key: { : ObjectId('5cbc813227b2ca2864b3c66a') }
    at Function.create (D:\app\server\node_modules\mongodb\node_modules\mongodb-core\lib\error.js:43:12)
    at toError (D:\app\server\node_modules\mongodb\lib\utils.js:149:22)
    at coll.s.topology.insert (D:\app\server\node_modules\mongodb\lib\operations\collection_ops.js:859:39)
    at D:\app\server\node_modules\mongodb\node_modules\mongodb-core\lib\connection\pool.js:397:18
    at process._tickCallback (internal/process/next_tick.js:61:11)

I am not inserting _id columns value and allowing it to be system generated. Here is the output of getindexes.

> db.Tab2017.getIndexes()
[
        {
                "v" : 2,
                "key" : {
                        "_id" : 1
                },
                "name" : "_id_",
                "ns" : "app.Tab2017"
        }
]
>

When i insert same object through mongo shell command line, it works without error. Looks like javascript does not wait for mongodb insert operation to complete.

Answer 1

You might need to drop the index,then try to insert .

db.collection.dropIndex()

Answer 2

_id field in MongoDB is a unique key field. You cannot insert duplicate values to the _id column.

For example, you have a document with _id value equal to 1 exist in the collection and you are trying to insert one more document with same _id value(1) you will get the E11000 duplicate key error.

In your case, you are not generating a new _id value when inserting the second document which results in a duplicate error. Try creating a new _id for every insert or don't pass the _id value so that MongoDB backend will take care of this.

Answer 3

I have solved the problem myself. Nodejs performs asynchronous operation so it completes the loop but keeps inserting into mongodb collection as well. I noticed that, first operation always gets successful and fails for subsequent inserts. Somehow mongodb generates "_id" value for first insert and keeps that same "_id" in json objects. That's why it throws duplicate error. I just added one line to remove "_id" from json object before mongo insert and it worked.

Here is my modified code.

for (var i = 0; i < 5; i++) {        
            jsonData["test"] = "line"; 
            **delete jsonData["_id"];**
                console.log('LINE_'+i+'- '+JSON.stringify(jsonData));
                collection.insertOne(jsonData, (err, result) => {                       
                    if(err) { console.dir(err); }                           
                    console.log('mongodb insert done');             
                })              
        }