TypeScript: Regression in allowing Virtuals with Setters in Document creation/initialization after upgrading to v9

[nikzanda]

Prerequisites

• I have written a descriptive issue title

Mongoose version

9.1.6

Node.js version

24.11.0

MongoDB version

6.0.2

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

No response

Issue

After upgrading from Mongoose 8 to Mongoose 9, I've encountered a strict typing issue when initializing documents that contain subdocuments with virtual setters.

In Mongoose 8, it was possible to pass a value to a virtual field (which has a setter) during document creation. In Mongoose 9, the TypeScript compiler throws an error, forcing the use of the raw database paths instead of the virtual path.

Schema setup

I have a decimalSchema used as a subdocument. It stores a number as base and exponent but exposes a value virtual for ease of use:

import {
  HydratedSingleSubdocument,
  Model,
  Schema,
  SchemaOptions,
  SchemaTypes,
} from 'mongoose';

export interface IDecimal {
  base: number;
  exponent: number;
}

export interface IDecimalVirtuals {
  value: number;
}

export type DecimalInstance = HydratedSingleSubdocument<IDecimal, IDecimalVirtuals>;

type DecimalModelType = Model<IDecimal, {}, {}, IDecimalVirtuals, DecimalInstance>;

type DecimalSchemaOptions = SchemaOptions<
  IDecimal,
  {},
  {},
  {},
  IDecimalVirtuals,
  DecimalInstance,
  DecimalModelType
>;

const options: DecimalSchemaOptions = {
  _id: false,
  toJSON: { virtuals: true },
  toObject: { virtuals: true },
};

const decimalSchema = new Schema<
  IDecimal,
  DecimalModelType,
  {},
  {},
  IDecimalVirtuals,
  {},
  DecimalSchemaOptions,
  IDecimal,
  DecimalInstance
>({
  base: {
    type: SchemaTypes.Number,
    required: true,
  },
  exponent: {
    type: SchemaTypes.Number,
    required: true,
  },
}, options);

decimalSchema.virtual('value')
  .get((_value, _virtual, doc) => fromDecimal(doc)) // returns number
  .set((value: number, _virtual, doc) => doc.set(toDecimal(value))); // converts number to IDecimal

export default decimalSchema;

The issue

When I try to create a parent document containing this subdocument:

// Parent Schema usage
const parentSchema = new Schema({
  quantity: decimalSchema
});

// Mongoose 8: Worked fine
// Mongoose 9: Type Error
const doc = new ParentModel({
  quantity: { value: 10 } 
});

I would like to know if there is a recommended way in Mongoose 9 to allow virtuals with setters to be accepted as valid input types during document initialization/creation, or if this is a regression in the new type inference engine.

Ideally, the inferred type for the document constructor should include keys from IDecimalVirtuals if they have a setter defined, or allow us to merge virtuals into the "Input" type of the schema more easily.

[vkarpov15]

What is the compiler error you get? You would only get a compiler error if you did ParentModel.create({ quantity: { value: 10 } }). As you wrote it, new ParentModel({ quantity: { value: 10 } }) would not cause a compiler error.

[nikzanda]

Sorry, you're right. The error only occurs when using Model.create({}), not new Model({}). The error message is:

const bom = await Bom.create({
    stockable: prototype,
    rows: [{
      _id: '123456',
      // quantity: toDecimal(0),
      quantity: { value: 0 },
    }],
  });

No overload matches this call.
  The last overload gave the following error.
    Object literal may only specify known properties, and 'value' does not exist in type '{ base?: number | undefined; exponent?: number | undefined; } | { base?: number | undefined; exponent?: number | undefined; }'.ts(2769)
bomRow.d.ts(13, 5): The expected type comes from property 'quantity' which is declared here on type '{ _id?: string | undefined; category?: ObjectId | { _id?: ObjectId | undefined; $assertPopulated?: (<Paths = {}>(path: string | string[], values?: Partial<Paths> | undefined) => Omit<...> & Paths) | undefined; ... 61 more ...; updatedAt?: Date | undefined; } | undefined; ... 9 more ...; updatedAt?: Date | undefined;...'
models.d.ts(357, 5): The last overload is declared here.