Aggregation Typing not working as expected

[jeff-titan]

Hey! Love the project, really hope Papr makes it big!

I'm trying to figure out how to get proper typing out of the aggregation pipeline. Docs reference that says this is possible:
https://plexinc.github.io/papr/#/api/model?id=aggregate

Returns:
Promise<Array<Aggregate>> A custom data type based on the pipeline steps

Given these two models:

import { types, schema } from 'papr';
import papr from '@db/papr';

export enum Kind {
  dog = 'dog',
  cat = 'cat',
}

const petSchema = schema({
  name: types.string({ required: true }),
  owner: types.objectId({ required: true }),
  kind: types.enum(Object.values(Kind), { required: true }),
});

export type PetDocument = typeof petSchema[0];

const Pet = papr.model('pets', petSchema);

export default Pet;

import { types, schema } from 'papr';
import papr from '@db/papr';

const ownerSchema = schema({
  firstName: types.string({ required: true }),
  lastName: types.string({ required: true }),
  address: types.object(
    {
      line1: types.string({ required: true }),
      line2: types.string(),
      city: types.string({ required: true }),
      state: types.string({ required: true }),
      zip: types.string({ required: true }),
      country: types.string({ required: true }),
    },
    { required: true }
  ),
  phoneNumber: types.string(),
});

export type OwnerDocument = typeof ownerSchema[0];

const Owner = papr.model('owners', ownerSchema);

export default Owner;

I would expect the below snippet to return a type where owner is fully enumerated, but I'm still seeing that it's type ObjectId. Actually the entire return type of the pipeline is just PetDocument.
When I add a project stage to this pipeline and try and select only a few fields, it also doesn't change the return type.

This does work at runtime as expected (ie I can get the owner.address off of the $lookup => $unwind). We just don't get type hinting from tooling and actually gives us some tsc errors (even though, again, it works at runtime).

async function findPetsByOwnerState(state: string) {
  const res = await Pet.aggregate([
    {
      $lookup: {
        from: 'owners',
        localField: 'owner',
        foreignField: '_id',
        as: 'owner',
      },
    },
    {
      $unwind: '$owner',
    },
    {
      $match: {
        'owner.address.state': state,
      },
    }
  ]);

[avaly]

Supporting truly typed aggregate operations is out of the scope of papr. The MongoDB aggregation pipeline syntax is extremely complicated that adding support for this would be very difficult.

The papr docs around aggregate() should be clearer in this regard though. The following is currently supported:

const res = await Pet.aggregate<YourCustomType>([ ... ]);

With the caveat that you'll have to define your own result type based on the aggregation operations.

[jeff-titan]

Thanks for the response!