Mongoose, CastError: Cast to Array failed for valu

Question

I am trying to create the model for my mongodb database using mongoose. This is what I am trying to do:

var Class = mongoose.model('Class', {className: String, marks: [{type: Number}], grades: [{type: Number}]});
var User = mongoose.model('User', {email: String, classes: [Class] });


//Lets create a new user
var class1 = new Class({className: 'aaa', marks: [72, 88, 63], grades: [30, 40, 30]});
var user1 = new User({email: '[e-mail]', classes: [class1]});

Saving class1 seems to work okay but when I check mongodb, this is displayed:

{ 
  "_id" : ObjectId("someId"), 
  "className" : "TEST1234", 
  "grades" : [ 30, 40, 30 ], 
  "marks" : [ 72, 88, 63 ], 
  "__v" : 0 
}

What is "__v : 0"?

Saving the user is not successful at all, this is the following error:

ValidationError: CastError: Cast to Array failed for value "{ marks: [ 72, 88, 63 ], grades: [ 30, 40, 30 ], _id: someId, className: 'TEST1234' }" at path "classes" `

What exactly does the error mean? Why is it casting anything to a array? Shouldn't classes: [Class] be an array of type class?

Answer 1

Just for Update

Now Mongoose supports subdocuments, which are the documented way to nest arrays,

var arraySchema = new Schema({
    property: String
});

var objectSchema = new Schema({
    arrays: [arraySchema]
});

Sources

http://mongoosejs.com/docs/schematypes.html