Question 115780 in Mongodb Question posted in
The official documentation can be found here.

Mongodb – TypeError: Cannot read properties of undefined (reading 'length') when using mongoose

i’m making a todolist (angela yu), i’m trying to write to a new database, but i keep getting error.this is the error:

C:UserstunjiDesktopwebdevtodolist-v2-starting-filesnode_modulesmongooselibmodel.js:3519
        for (let i = 0; i < error.writeErrors.length; ++i) {
                                              ^

TypeError: Cannot read properties of undefined (reading 'length')
    at C:UserstunjiDesktopwebdevtodolist-v2-starting-filesnode_modulesmongooselibmodel.js:3519:47
    at collectionOperationCallback (C:UserstunjiDesktopwebdevtodolist-v2-starting-filesnode_modulesmongooselibdriversnode-mongodb-nativecollection.js:133:26)
    at Timeout.<anonymous> (C:UserstunjiDesktopwebdevtodolist-v2-starting-filesnode_modulesmongooselibdriversnode-mongodb-nativecollection.js:160:11)        
    at listOnTimeout (node:internal/timers:564:17)
    at process.processTimers (node:internal/timers:507:7)

this is the code:

const express = require("express");
const bodyParser = require("body-parser");
const mongoose = require("mongoose");

const app = express();
mongoose.connect('mongodb://localhost:27017/todolistDB');

app.set('view engine', 'ejs');

app.use(bodyParser.urlencoded({extended: true}));
app.use(express.static("public"));


// const itemsSchema = {
//   name: String
// };

const itemsSchema = new mongoose.Schema({
  name: String
});

const Item = mongoose.model("Item", itemsSchema);

const item1 = new Item({name: "Workout"});
const item2 = new Item({name: "skydive"});
const item3 = new Item({name: "bungee"});

const defaultItems = [item1, item2, item3];

Item.insertMany(defaultItems, function(err){
  if (err){
    console.log(err + "yea");
  } else {
    console.log("good to go");
  }
});

app.get("/", function(req, res) {


  res.render("list", {listTitle: "Today", newListItems: items});

});

app.listen(3000, function() {
  console.log("Server started on port 3000");
});

i’ve checked the server, deleted and installed the node module ,everything, still no fix,nothing at all

Tags:

3

Answers


  1. 0

    I think you cannot connect to mongoose, as per mongoose documentation connect is an async method.

    Try waiting for connection to be established, then write to the database

    example:

    const express = require("express");
const bodyParser = require("body-parser");
const mongoose = require("mongoose");

const app = express();
app.set('view engine', 'ejs');

app.use(bodyParser.urlencoded({extended: true}));
app.use(express.static("public"));

app.get("/", function(req, res) {
  res.render("list", {listTitle: "Today", newListItems: items});
});

app.listen(3000, function() {
  console.log("Server started on port 3000");
});

async function connect() {
    try {
        await mongoose.connect('mongodb://localhost:27017/todolistDB');
        console.log('Connected to MongoDB');
    } catch (error) {
        console.log('Could not connect to MongoDB');
        throw error;
    }
    const itemsSchema = new mongoose.Schema({
        name: String
    });
      
    const Item = mongoose.model("Item", itemsSchema);  
    const item1 = new Item({name: "Workout"});
    const item2 = new Item({name: "skydive"});
    const item3 = new Item({name: "bungee"});
    
    const defaultItems = [item1, item2, item3];
    
    Item.insertMany(defaultItems, function(err){
    if (err){
        console.log(err + "yea");
    } else {
        console.log("good to go");
    }
    });
      
}

connect();

``
    Login or Signup to reply.
  2. 0

    Instead of using localhost:27017
    Rather use 127.0.0.1:27017

    So it should look like this:

    mongoose.connect("mongodb://127.0.0.1:27017/todolistDB")
    Login or Signup to reply.
  3. 0

    To solve this problem you have first to comment the tiem.insert and your array

    const itemsSchema = new mongoose.Schema({
  name: String
});

const Item = mongoose.model("Item", itemsSchema);

const item1 = new Item({name: "Workout"});
const item2 = new Item({name: "skydive"});
const item3 = new Item({name: "bungee"});

// const defaultItems = [item1, item2, item3];

// Item.insertMany(defaultItems, function(err){
//   if (err){
//     console.log(err + "yea");
//   } else {
//     console.log("good to go");
//   }

    after that run the app.js in the terminal, now move to the mongo or mongosh and write show dbs, you should now see the todolistDB already. so now you could go and uncomment the rest of your code and run thr app.js again

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search