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 I am following a tutorial that is out of date in some areas, for instance their version of Jquery used a totally different format for some functions and I had to do a lot of changing around. But I think I am down to one last major problem that I can't seem to find a fix for. In my Schema variable I've got the _id, username, and password types

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

but when I go to try to add a new user to my app, instead of getting the alert I am supposed to get, it pops up as [object Object] and nothing gets added to the database. Then this error pops up in the mongo cmd

"Error: document must have an _id before saving".

I've tried commenting out the _id line and I get the right message but still nothing shows up in my database.

Answer 1

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 2

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 3

_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 4

Do not specify _id: mongoose.Schema.ObjectId in your model. The system creates the id if you leave out the _id like so:

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