useRxData doesn't support findOne

[nirvdrum]

I've run into a type definition error when providing useRxData with a query constructor that uses findOne. I think the issue is that findOne can return null, while find always returns a value, even if that value is an empty array. The TypeScript error isn't the clearest thing in the world:

TS2769: No overload matches this call.
  Overload 1 of 3, '(collectionName: string, queryConstructor: QueryConstructor<TodoChainDoc> | undefined): RxQueryResultDoc<TodoChainDoc>', gave the following error.
    Argument of type '(collection: RxCollection<TodoChainDoc>) => RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}> | null>' is not assignable to parameter of type 'QueryConstructor<TodoChainDoc>'.
      Type 'RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}> | null>' is not assignable to type 'RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}>> | RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}>[]> | undefined'.
        Type 'RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}> | null>' is not assignable to type 'RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}>>'.
          The types of '$.value' are incompatible between these types.
            Type 'RxDocument<TodoChainDoc, {}> | null' is not assignable to type 'RxDocument<TodoChainDoc, {}>'.
              Type 'null' is not assignable to type 'RxDocument<TodoChainDoc, {}>'.
  Overload 2 of 3, '(collectionName: string, queryConstructor: QueryConstructor<TodoChainDoc> | undefined, options?: Override<UseRxQueryOptions, { ...; }> | undefined): RxQueryResultDoc<...>', gave the following error.
    Argument of type '(collection: RxCollection<TodoChainDoc>) => RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}> | null>' is not assignable to parameter of type 'QueryConstructor<TodoChainDoc>'.
  Overload 3 of 3, '(collectionName: string, queryConstructor: QueryConstructor<TodoChainDoc> | undefined, options?: Override<UseRxQueryOptions, { ...; }> | undefined): RxQueryResultJSON<...>', gave the following error.
    Argument of type '(collection: RxCollection<TodoChainDoc>) => RxQuery<TodoChainDoc, RxDocument<TodoChainDoc, {}> | null>' is not assignable to parameter of type 'QueryConstructor<TodoChainDoc>'.

I can manually query against the collection or just use find and unwrap the array in the meanwhile. Please let me know if I can be of any assistance. I couldn't see a simple way to change the return type based on using find vs findOne and I don't want to break code on existing users by forcing null as a potential return value on all queries. Maybe the solution is a new hook (e.g, useRxDataOne)?

[cvara]

Hey @nirvdrum. Can you please provide a concrete example? Also which versions of rxdb-hooks/rxdb are you using?

[nirvdrum]

Hi @cvara. Thanks for taking a look. I'm using rxdb-hooks 4.0.1.

What I was trying to do was:

const todosQuery = (collection: any) => {
    collection.findByIds(todoChain.todo_ids)
};
const { result: todoMap, isFetching } = useRxData('todos', todosQuery);

Generally I use type annotations so I don't get back a generic RxDocument or RxCollection, but I couldn't find a signature that would work. So, here I'm just using the any type and letting the type inference engine handle things up to the useRxData call. The TypeScript error I received was:

TS2769: No overload matches this call.
  Overload 1 of 3, '(collectionName: string, queryConstructor: QueryConstructor<unknown> | undefined): RxQueryResultDoc<unknown>', gave the following error.
    Argument of type '(collection: any) => void' is not assignable to parameter of type 'QueryConstructor<unknown>'.
      Type 'void' is not assignable to type 'RxQuery<unknown, RxDocumentBase<unknown, {}>> | RxQuery<unknown, RxDocumentBase<unknown, {}>[]> | undefined'.
  Overload 2 of 3, '(collectionName: string, queryConstructor: QueryConstructor<unknown> | undefined, options?: Override<UseRxQueryOptions, { json?: false | undefined; }> | undefined): RxQueryResultDoc<...>', gave the following error.
    Argument of type '(collection: any) => void' is not assignable to parameter of type 'QueryConstructor<unknown>'.
  Overload 3 of 3, '(collectionName: string, queryConstructor: QueryConstructor<unknown> | undefined, options?: Override<UseRxQueryOptions, { json: true; }> | undefined): RxQueryResultJSON<...>', gave the following error.
    Argument of type '(collection: any) => void' is not assignable to parameter of type 'QueryConstructor<unknown>'.

What I've ended up doing is:

const todosCollection = useRxCollection<TodoDoc>('todos');

useEffect(() => {
  const subscription = todosCollection?.findByIds$(todoIds).subscribe((todos) => {
      // todos is an ES6 Map<string, TodoDocument>.
      console.log("todo map", todos.get("some_id"));
  });

  return () => subscription?.unsubscribe();
}, [todoIds, todosCollection]);

While this works, I really like how rxdb-hooks handles all of the annoying subscribe and unsubscribe logic along with return any "loading" state.

Please let me know if you need anymore info.