Defining nested discriminator with the discriminator key as part/property of the sub-document

[chandu]

Let's say I have the typescript models as follows:

interface LibraryBook {
isDigital: false;
name: string
}
interface AmazonBook {
 name: string;
 isDigital: true
}
interface Author {
 name: string;
 book: Book
}

 type Book = AmazonBook | LibraryBook;

How can define Author schema and subsequently Book schema I add a discriminator to the book property of Author model leveraging isDigital property?

Based on my understanding w.r.t documentation @ https://mongoosejs.com/docs/discriminators.html the only way I can think of is by defining a schema matching the following Author definition

interface Author {
 name: string;
 book: {
  isDigital: boolean;
  bookData: Book 
 }
}

// Mongoose Schema

const bookSchema = new Schema({}, { discriminatorKey: "isDigital" });
// Casting as mongoose.Schema.Types.DocumentArray as the discriminator is not availabel int typescipt definitions
(bookSchema.path('bookData') as mongoose.Schema.Types.DocumentArray).discriminator("YES", <schema of amazon book>)
(bookSchema.path('bookData') as mongoose.Schema.Types.DocumentArray).discriminator("NO", <schema of library book>)
const authorSchema = new Schema<Author & Document>({
  name: String,
  book: bookSchema,
});