MongoDB - Error: document must have an _id before saving

Question

I\'ve been struggling so much with this project. I am following a tutorial that is out of date in some areas, for instance their version of Jquery used a totally different f

Answer 1

_id is added automatically by MongoDb.

If you want to keep _id on your data structure be sure to initialize correctly:

var obj = new UserSchema({ 
    "_id": new ObjectID(), 
    "username": "Bill", 
    "password" : "...." 
});

Answer 2

Its pretty simple:

1. If you have declared _id field explicitly in schema, you must initialize it explicitly
2. If you have not declared it in schema, MongoDB will declare and initialize it.

What you can't do, is to have it in the schema but not initialize it. It will throw the error you are talking about

Answer 3

Try below snippet I wanted to name _id as userId you can do without it as well.

var Schema = mongoose.Schema,
ObjectId = Schema.ObjectId;

var UserSchema = new Schema({
    username: String,
    password: String
});
UserSchema.virtual('userId').get(function(){
    return this._id;
});

Answer 4

No need to specify the document _id in your model. The system generates the id automatically if you leave out the _id like so:

var UserSchema = new mongoose.Schema({    
    username: String,
    password: String
}); 

That being said, if you still want to generate the _id yourself, see the answers above.

Answer 5

You can write your model without _id so it will be autogenerated

or

you can use .init() to initialize the document in your DB.

Like:

const mongoose = require('mongoose');

const UserSchema = mongoose.Schema({
  _id: mongoose.Schema.Types.ObjectId,
  username: String,
  password: String
})

module.exports = mongoose.model('User', UserSchema);

and then

const User = require('../models/user');

router.post('/addUser',function(req,res,next){

  User.init() // <- document gets generated

  const user = new User({
    username: req.body.username,
    password: req.body.password
  })

  user.save().then((data)=>{
    console.log('save data: ',data)
   // what you want to do after saving like res.render
  })
}

Answer 6

In my case, I accidentally had the following at the end of my Schema. Removing that worked:

{ _id: false }