Using reducer state inside useEffect

Question

Hello All 👋🏻 I have a question about our favorite Hooks API!

What am I trying to do?

I am trying to fetch photos from some remote system. I store the blob urls for these photos in my reducer state keyed by an id.

I have a helper function wrapped in the memoized version returned by the useCallback hook. This function is called in the useEffect I have defined.

The Problem ⚠️

My callback a.k.a the helper function depends on part of the reducer state. Which is updated every time a photo is fetched. This causes the component to run the effect in useEffect again and thus causing an infinite loop.

component renders --> useEffect runs ---> `fetchPhotos` runs --> after 1st photo, reducer state is updated --> component updates because `useSelector`'s value changes ---> runs `fetchPhotos` again ---> infinite

const FormViewerContainer = (props) => {
  const { completedForm, classes } = props;

  const [error, setError] = useState(null);

  const dispatch = useDispatch();
  const photosState = useSelector(state => state.root.photos);

  // helper function which fetches photos and updates the reducer state by dispatching actions
  const fetchFormPhotos = React.useCallback(async () => {
    try {
      if (!completedForm) return;
      const { photos: reducerPhotos, loadingPhotoIds } = photosState;
      const { photos: completedFormPhotos } = completedForm;
      const photoIds = Object.keys(completedFormPhotos || {});
      
      // only fetch photos which aren't in reducer state yet
      const photoIdsToFetch = photoIds.filter((pId) => {
        const photo = reducerPhotos[pId] || {};
        return !loadingPhotoIds.includes(pId) && !photo.blobUrl;
      });

      dispatch({
        type: SET_LOADING_PHOTO_IDS,
        payload: { photoIds: photoIdsToFetch } });

      if (photoIdsToFetch.length <= 0) {
        return;
      }

      photoIdsToFetch.forEach(async (photoId) => {
        if (loadingPhotoIds.includes(photoIds)) return;

        dispatch(fetchCompletedFormPhoto({ photoId }));
        const thumbnailSize = {
          width: 300,
          height: 300,
        };

        const response = await fetchCompletedFormImages(
          cformid,
          fileId,
          thumbnailSize,
        )

        if (response.status !== 200) {
          dispatch(fetchCompletedFormPhotoRollback({ photoId }));
          return;
        }
    
        const blob = await response.blob();
        const blobUrl = URL.createObjectURL(blob);

        dispatch(fetchCompletedFormPhotoSuccess({
          photoId,
          blobUrl,
        }));
      });
    } catch (err) {
      setError('Error fetching photos. Please try again.');
    }
  }, [completedForm, dispatch, photosState]);

  // call the fetch form photos function
  useEffect(() => {
    fetchFormPhotos();
  }, [fetchFormPhotos]);

  ...
  ...
}

What have I tried?

I found an alternative way to fetch photos a.k.a by dispatching an action and using a worker saga to do all the fetching. This removes all the need for the helper in the component and thus no useCallback and thus no re-renders. The useEffect then only depends on the dispatch which is fine.

Question ?

I am struggling with the mental modal of using the hooks API. I see the obvious problem, but I am not sure how could this be done without using redux middlewares like thunks and sagas.

Edit:

reducer function:

export const initialState = {
  photos: {},
  loadingPhotoIds: [],
};

export default function photosReducer(state = initialState, action) {
  const { type, payload } = action;
  switch (type) {
    case FETCH_COMPLETED_FORM_PHOTO: {
      return {
        ...state,
        photos: {
          ...state.photos,
          [payload.photoId]: {
            blobUrl: null,
            error: false,
          },
        },
      };
    }
    case FETCH_COMPLETED_FORM_PHOTO_SUCCESS: {
      return {
        ...state,
        photos: {
          ...state.photos,
          [payload.photoId]: {
            blobUrl: payload.blobUrl,
            error: false,
          },
        },
        loadingPhotoIds: state.loadingPhotoIds.filter(
          photoId => photoId !== payload.photoId,
        ),
      };
    }
    case FETCH_COMPLETED_FORM_PHOTO_ROLLBACK: {
      return {
        ...state,
        photos: {
          ...state.photos,
          [payload.photoId]: {
            blobUrl: null,
            error: true,
          },
        },
        loadingPhotoIds: state.loadingPhotoIds.filter(
          photoId => photoId !== payload.photoId,
        ),
      };
    }
    case SET_LOADING_PHOTO_IDS: {
      return {
        ...state,
        loadingPhotoIds: payload.photoIds || [],
      };
    }
    default:
      return state;
  }
}