GraphQL and MongoDB - "Cast to Array failed" With Array [duplicate] - mongodb

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: 'aaa#some.com', 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

Man, I had a similar issue creating an Schema like this:
QuestionnaireSchema = mongoose.Schema({
formId: Number,
name: String,
questions: [
{
type: String,
title: String,
alternatives:[{
label: String,
value: "Mixed"
}]
}
]
});
My mistake was that I am using "type" as a field name and this is reserved word in mongoose.
I just change:
type: String,
to
formType: String,
and that works.
see: https://github.com/Automattic/mongoose/issues/1760

Answer 2

Explicitly defining the type rule on a property called type is allowed and won't throw an error. like this:
type: {type: String}

Answer 3

Try changing the class definition to :
var classSchema = mongoose.Schema({className: String, marks: [{type: Number}], grades: [{type: Number}]});
var userSchema = mongoose.Schema({email: String, classes: [classSchema] });
var User = mongoose.model('User',userSchema);
This is required since mongoose is not able to parse the object without a related schema. Now when you create a new Schema for the internal class object and refer it in the main userSchema mongoose should be able to parse your object.

Answer 4

Your model definition is incorrect, you should fix like below.
// var Schema = mongoose.Schema;
var User = mongoose.model('User',{
email: String,
classes: [ {type: Schema.Types.ObjectID, ref: 'Class'}]
});
var Class1 = new Class({/*yourDataWillBeHere*/})
Class1.save(function(err, classData) {
var User1 = new User({/*YourDataWillBeHere*/})
User1.classes.push(classData._id);
User1.save(function(err, userData) {
//make something with userData object
})
})
Then you can get fetched data using with populate() like this
User
.find()
.populate('classes')
.exec()

Answer 5

By default, if you have an object with key 'type' in your schema, mongoose will interpret it as a type declaration.
// Mongoose interprets this as 'loc is a String'
var schema = new Schema({ loc: { type: String, coordinates: [Number] } });
Changing the typeKey:
var schema = new Schema({
// Mongoose interpets this as 'loc is an object with 2 keys, type and coordinates'
loc: { type: String, coordinates: [Number] },
// Mongoose interprets this as 'name is a String'
name: { $type: String }
}, { typeKey: '$type' }); // A '$type' key means this object is a type declaration
Link: http://mongoosejs.com/docs/guide.html#typeKey

Answer 6

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

Answer 7

I got a similar issue using mongoose 5.7.0+ using double nested schema.
Except it wasn't related to the keyword type but a mongoose validation bug.
https://github.com/Automattic/mongoose/issues/8472
Temporary workaround: Use Schema.Types.Mixed for the subschema