Question: how to handle get/set for async state

Hi, after watching the awesome video on Recoil, I almost rushed to delete Redux and use Recoil on a large production project with no questions asked. It’s a miracle though that I decided to first try it out.

I’ve seen similar questions in the issues already, but they don’t seem to answer the question - how do you handle setting an async state?. E.g. we have a companies list, and we want to fetch the companies from the API, and then add new company to the list. From what I understand, I could do sth like this:

export const companiesState = atom({
  key: 'companiesState',
  default: [],
});
export const companiesQuery = selector({
  key: 'companiesSelector',
  get: async ({ get }) => {
    get(companiesState);
    const response = await fetch('http://localhost:9000/companies');
    return await response.json();
  },
  set: async ({ set, get }, newCompany) => {
    const response = await fetch('http://localhost:9000/companies', {
      method: 'POST',
      body: JSON.stringify(newCompany),
      headers: {
        'Content-Type': 'application/json',
      },
    });
    const company = await response.json();
    set(companiesState, [company]);
  },
});

Confusing parts for me are:

• do I need to set the get(companiesState); dependency. All I need is to e.g. push the new company to the list. I could do companiesState || fetch(...) in the getter, but that doesn’t seem to be a good thing(?) as there wouldn’t be an easy way to refresh the state
• what’s the difference between selector and atom? As far as I can get, the only difference is that selector can be readonly, as atom is always writable. The docs state that selector is a derived state but then I see in the articles and issues selector being used as a state, not always derived from something
• would you say that in this case, the getting/posting data should be handled in the useEffect in the component instead of the state itself?

Anyway, the library looks very promising - kudos to everyone working on it!

[drarmstr]

@bentron2000 - Here’s the proposed API. We don’t want to expose set during a selector get operation, as that would essentially lead to synchronous side-effects during render.

[drarmstr]

See these updated guides: async requests and atom effects.