Definitelytyped: @types/mongodb - Generics does not work with v3.2.x or v3.3.x

[lirbank]

Using generics to set the schema does not seem to work since v3.2.x of @types/mongodb

See this example using @types/mongodb v3.1.32 (works):
https://codesandbox.io/s/typesmongodb-3132-works-nmxbc

See this example using @types/mongodb v3.3.6 (type error):
https://codesandbox.io/s/typesmongodb-336-type-error-onshs

Reproduction (same as CodeSandbox):

import { Db, Collection } from "mongodb";

export default class Model<Schema extends { _id: string }> {
  private readonly db: Db;
  private readonly collection: Collection<Schema>;

  public constructor(db: Db, collectionName: string) {
    this.db = db;
    this.collection = db.collection(collectionName);
  }

  public findOneById(id: string) {
    // This gives the type error below on @types/mongodb v3.3.6
    return this.collection.findOne({ _id: id });
  }
}

TS Error:

Argument of type '{ _id: string; }' is not assignable to parameter of type 'FilterQuery<Schema>'.
  Type '{ _id: string; }' is not assignable to type '{ [P in keyof Schema]?: MongoAltQuery<Schema[P]> | QuerySelector<MongoAltQuery<Schema[P]>> | undefined; }'.

Authors: @CaselIT @alanmarcell @bitjson @dante-101 @mcortesi @EnricoPicci @AJCStriker @julien-c @daprahamian @denys-bushulyak @BastienAr @sindbach @geraldinelemeur @jishi @various89 @angela-1 @hector7 @floric @erikc5000 @Manc @jloveridge @ranguna @HosseinAgha @albertossilva

[HosseinAgha]

Hi @lirbank,
This looks to me like a TypeScript mapped types bug.
I can confirm that this does __not__ work:

  const genericFunc = async <Schema extends { _id: string }>() => {
    type a = { [P in keyof Schema]: Schema[P] };
    const b: a = { _id: 'sd' };
  }

And this does work:

  type Schema2 = { _id: string };
  type a2 = { [P in keyof Schema2]: Schema2[P] };
  const b2: a2 = { _id: 'sd' };

We've implement collection.find types using mapped types.
There is not much that we can do here. I think you should open (look for) a TypeScript issue.
I have to admit that you are doing a pretty complicated job with TypeScript generics (generic on top of generic on top of generic 😄) and TypeScript is an awesome language that even lets you handle these scenarios.

[jimbuck]

Agreed, this is definitely a bug! If you guys put a bug into the TypeScript repo then please don't forget to reference this PR. I'd love to see where this goes.

My demo code: typescriptlang.org

[kevinclarkadstech]

Grrrrr I found the same issue using a generic service. :/ TypeScript has been a little "dumber" lately it seems. For a workaround I just asserted using as:

collection.findOne({id: 2 } as FilterQuery<Entity<T>>, (error, result) => {

                    })

[HosseinAgha]

Hi @lirbank,
According to (your issue) https://github.com/microsoft/TypeScript/issues/35077 and (my issue) https://github.com/microsoft/TypeScript/issues/35647 TypeScript (and mongo typings) work as expected in this scenario.
I don't think our mongo driver generics can work with other generics in a format that you expect them to. __We need the keyof Schema__ in order to generate right typing for mongo methods and keyof does not have enough information about the generic type in this scenario (checkout https://github.com/microsoft/TypeScript/issues/35647#issuecomment-566543066).
I think we have enough workarounds (including yours) for this issue to close.

[lirbank]

Hi @HosseinAgha - I agree, looks like we're at the end of the road with this one.

Thanks for looking into it!