Using Angular 21 signal forms submit function with rxMethod from ngrx is impossible, please create a new function to return promise to be able to be used in angular 21 signal forms

[rezaimn]

Which @ngrx/* package(s) are relevant/related to the feature request?

signals

Information

I was trying out the new feature from Angular 21 and wanted to use it with ngrx signal store. However, I realized it is impossible to use it in the signal forms submit function because it requires a promise in return, but rxMethod returns only a destroy. Therefore, we need a function that returns a promise instead.

In this article I explained the issue and created a new method called rxPromiseMethod to be used instead of rxMethod within withMethod(). You can find some examples there.

https://medium.com/@mohammadrezaimn/rxpromisemethod-bridging-ngrx-signal-store-with-angulars-signal-forms-f80483adcb35

Describe any alternatives/workarounds you're currently using

There is a withMutation function from the @angular-architects/ngrx-toolkit library, but the issue is that you can only send a payload to it, and the types are tightly coupled with the HTTP request DTO, which is not good.

I would be willing to submit a PR to fix this issue

• Yes
• No

[rainerhahnekamp]

Since it wouldn't be a feature for Signal Forms only, I can see the possibility for rxMethod to change its type from

type RxMethodRef = {
  destroy: () => void;
};

to

type RxMethodRef<T> = {
  destroy: () => void;
} & Promise<{
  value: T
}>

Given, that I was also involved in the mutation features in the toolkit, we will be facing a challenge with rxMethod: RxJS' operators filter, exhaustMap, etc. can just skip values, which means we are dealing with a Promise that never resolves. Such a thing does not exist. That's also why lastValueFrom would throw an error if an Observables completes without emitting at least one value.

The toolkit solved this by not allowing pipe operators. Users can only choose between 4 custom flattening operators which detect dropped values and would be able to resolve the Promise. We can't do that in rxMethod.

So we will have to find an answer on how to deal with it.

[rainerhahnekamp]

I changed my mind. For mutation it might be very important to have a guranteed Promise which resolves, but rxMethod is more generic.

Since lastValueFrom & firstValueFrom from RxJS also produce Promises which never resolve nor reject, I think the change to RxMethodRef should be doable.

It wouldn't even be a breaking change, but should still be planned for v21, if we decide to move forward.

type RxMethodRef<T> = {
  destroy: () => void;
} & Promise<{
  value: T
}>

The question is, if we want to provide the same for signalMethod as well.