selectHasEntitiesByPredicate

[leon]

Using the entity store, I have the need to check if there are any entities that match a predicate.

const items = [
{
  id: 1,
  favorite: true
},
{
  id: 2,
  favorite: false
}
]

I would now like to check if any of the items are favorite: true

const hasFavorite$: Observable<boolean> = store.pipe(
  selectHasEntitiesByPredicate(i => i.favorite)
)

I could use the selectEntitiesCountByPredicate but that means that it will loop through all entities, even if the first one is a favorite.

I suggest we implement a new function that uses the .some() method
https://github.com/ngneat/elf/blob/master/packages/entities/src/lib/entity.utils.ts#L36

export function hasIdsByPredicate<
  S extends EntitiesState<Ref>,
  Ref extends EntitiesRef
>(state: S, ref: Ref, predicate: ItemPredicate<getEntityType<S, Ref>>) {
  const { idsKey, entitiesKey } = ref;

  const entities = state[entitiesKey];
  return state[idsKey].some((id: getIdType<S, Ref>) =>
    predicate(entities[id])
  );
}

If I put together a PR, would this be something we could add?

[NetanelBasal]

IMHO it seems like premature optimization. How many entities do you have?

[leon]

A couple of thousand at the most, so it's probably not that a big computation to base it on the count.

or what would you suggest is the best way to check if the store has entities based on a predicate?

[NetanelBasal]

Yes. Unless you run it frequently, you should not run into any performance issues. I'd use count.