Using an argument for computed filtering in signal store

[blackholegalaxy]

Hi! Signal store is really great. I'm currently rewriting ngrx store selectors in computed. We used factory selectors to pass an argument to underlying selector like this was discussed on props deprecation documentation:

export const hasRight = (rightCode: RightCode) => createSelector(selectUser, (user) => {
    return user?.rights?.indexOf(rightCode) !== -1;
});

How that kind of things be achievable in signal store.

withComputed((store) => ({
    userById: (userId: string) => computed(() => store.users()[userId])
  })),

This produces an error:

Type '(userId: string) => Signal<any>' is not assignable to type 'Signal<unknown>'.
  Type '(userId: string) => Signal<any>' is not assignable to type '() => unknown'.
    Target signature provides too few arguments. Expected 1 or more, but got 0.

My question may be dumb. I don't want to put all filtering logic in components.

[rainerhahnekamp]

No, it is not dumb. In fact, a similar one was posted recently: #4651

So in your case, I'd put hasRight into withMethods or withProps. factory functions for computed don't work at the moment in withComputed.

[blackholegalaxy]

Thanks for the quick answer here !

Putting in withMethods clearly work. Will it still preserve kind of a "memoization" process?
I don't get how withProps can help in this case. Especially for a global signal store. Isn't withProps goal to "inject" some data available everywhere? How would the userId be passed when consuming this in a component?

[rainerhahnekamp]

I mean withProps, if you don't want to put it into withMethods (for whatever reasons).

When you want to have a memoization process you could use it in withComputed() with nested computeds.

Kind of like this:

withComputed(state => ({
  userRights: computed(() => {
    const users = state.users();
    const rightCodes = state.rightCodes();
    return Object.fromEntries(users.map(user => [
      user.id,
      Object.fromEntries(rightCodes.map(rightCode => [rightCode, user.rights.includes(rightCode]))
    ]))
  })
}))

The access from the store would then be

const userId = 1
const rightRole = 'admin';

const hasRight = state.userRights()[userId]['admin']

I am not sure if I would do that. It is memoized but depending on the frequency of potential changes and the amount of users, I'd go with putting it into withMethods.

[blackholegalaxy]

Ok that's very clear. It helps a lot.