NgRx Store: Add createChildSelectors function

[markostanimirovic]

Description

createChildSelectors function creates memoized and strongly typed child selectors based on the parent selector. There are two signatures:

First:

export const selectUserState = createFeatureSelector<fromUsers.State>('users');

export const {
  selectUsers,
  selectLoading,
  selectPagination,
} = createChildSelectors(selectUserState, fromUsers.initialState);

Second:

export const {
  selectUsers,
  selectLoading,
  selectPagination,
} = createChildSelectors(selectUserState, ['users', 'loading', 'pagination']);

Full description is available here: https://github.com/markostanimirovic/ngrx-child-selectors

Other information:

This feature can be implemented when we upgrade TypeScript version to 4.1 or higher.

If accepted, I would be willing to submit a PR for this feature

[x] Yes ❤️
[ ] No

[brandonroberts]

I think we should look at unifying this into something similar to createSlice in Redux Toolkit where you get the reducer key, reducer, the feature selector, and those child selectors for a given slice of state.

[markostanimirovic]

Hey @brandonroberts,

Did you mean something like this?

const {
  selectMusiciansState // 👈 feature selector
  selectMusicians,
  selectLoading,
  selectPagination
} = createSliceSelectors('musicians', initialState);

[brandonroberts]

Something more like

export const {
  reducer(maybe),
  featureKey,<- musicians
  featureSelector, <- createFeatureSelector('musicians') or selectMusiciansState
  selectLoading,
  selectCurrentMusicianId,
 ...
} = createFeature<State>({
  name: 'musicians',
  reducer
})

[markostanimirovic]

Looks good 👍

I will be happy to create a PR if you and the other team members agree :)

Btw, I would also add createChildSelectors function, because it can be used within createFeature function, but also independently, to create nested selectors for any selector.

[david-shortman]