GraphQL和MongoDB-“Cast to Array failed”和Array[duplicate]

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]});

保存 class1 似乎工作正常,但当我检查mongodb时,显示:

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

"__v : 0" 是吗?

ValidationError:CastError:Cast to Array失败,值为“{marks:[72,88,63], _身份证:某某, 类名:路径“classes”处的“TEST1234”}

这个错误到底是什么意思?为什么它要向数组中投射任何东西?不应该 classes: [Class] class 是吗?