Error/warn if `default` is the wrong type

[JosephScript]

Do you want to request a feature or report a bug?

Bug? Might be just unclear from the docs.

What is the current behavior?

Let's say you have two models, and one has an array of the other. You use ObjectId in an array. There are two ways to define this from what I can see:

// classroom.js
import { Schema, model } from 'mongoose'
const ClassroomSchema = new Schema(
  {
    name: { type: String, required: true, trim: true },
    students: {
      type: [Schema.Types.ObjectId],
      ref: 'Person',
      default: [],
    },
  },
)
  .set('toJSON', { virtuals: true })
export default model('Classroom', ClassroomSchema)

And:

// classroom.js
import { Schema, model } from 'mongoose'
const ClassroomSchema = new Schema(
  {
    name: { type: String, required: true, trim: true },
    students: [{
      type: Schema.Types.ObjectId,
      ref: 'Person',
      default: [],
    }],
  },
)
  .set('toJSON', { virtuals: true })
export default model('Classroom', ClassroomSchema)

If the current behavior is a bug, please provide the steps to reproduce.

When I use the first version of the schema, and create documents, then switch to the second version I can no longer load those documents. Are these underlyingly different? Is this a bug or expected?

What is the expected behavior?
I would expect them to behave the same.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

Node v14.1.0, Mongoose v5.8.11, MongoDB 4.0.14 Community.

[AbdelrahmanHafez]

In the second example, you're telling mongoose that students is an array of items, each item is an object id, and the default value for that item is an empty array.

Does trying the following schema work?

const ClassroomSchema = new Schema({
  name: { type: String, required: true, trim: true },
  students: {
    type: [{
      type: Schema.Types.ObjectId,
      ref: 'Person'
    }],
    default: []
  }
}).set('toJSON', { virtuals: true });

Is there a reason to favor the second example over the first one?

[JosephScript]

OK awesome that helps explain the difference. I don't necessarily need to use one or the other. It was more a confusion around the variety of ways to express an array and defaults together.

Personally, I find the example you have provided to be more clear. As I know the type is an array of ObjectIds for a certain ref, and the default for that is an empty array because if there is an old object that was saved before a type was added I don't want it to be undefined.

Whereas the first example seems like it is actually each item's default is an array (again, this is my personal preference).

Your example works, and because I find it more clear I can use that instead. My second example wasn't a bug, but a misunderstanding of the syntax. This can be closed.

Thank you for the help!