Why Mongoose Populate Required?

Question

Why Mongoose Populate Required?

Using mongoose populate: http://mongoosejs.com/docs/populate.html

It seams that mongoose is forcing me to declare a ref value for populate when I first create the document but in my case i don't have the ref info yet. When I try to create a new document while providing an empty string I get to my developer field I get:

{"message":"Cast to ObjectId failed for value \"\" at path \"developer\"","name":"CastError","type":"ObjectId","value":"","path":"developer"}

Object that I'm saving through mongoose:

var Project = {
  name: 'Coolproject',
  status: 'pending',
  developer: '',
  type: 'basic',
};

Project.create(req.body, function(err, project) {
  if(err) { return handleError(res, err); }
  return
});

My Model:

var ProjectSchema = new Schema({
  name: String,
  status: {type:String, default:'pending'},
  developer:{type: Schema.Types.ObjectId, ref: 'User'},
  type:String
});

Basically I need to set it later, but it doesn't seam like this is possible. Currently my work around is populate it with a dummy user until later but this is less than desirable.

Thoughts?

Update

Realized that if i provide a object id like value (55132a418b3cde5546b01b37) it lets me save the document. Very odd. Guess it just figured it can find the document moves on. Wondering why this doesn't happen for a blank value.

node.js
mongodb
mongoose

Answer 1

The problem is explained in the error message. You cannot save an Empty String in the place of an ObjectId. The field is not listed as 'required', so there is no problem leaving it out and saving the document.

Code correction:

// you can save this
var Project = {
    name: 'Coolproject',
    status: 'pending',
    type: 'basic',
};

Answer 2

You need to use the sparse index in model. So, the valid model can have developer equal to nil

var ProjectSchema = new Schema({
  name: String,
  status: {type:String, default:'pending'},
  developer:{type: Schema.Types.ObjectId, ref: 'User', sparse:true},
  type:String
});

See http://mongoosejs.com/docs/api.html#schematype_SchemaType-sparse and http://docs.mongodb.org/manual/core/index-sparse/ for additional info