Normalizr - where would I modify an entity?

Question

So I ran ahead and normalized all the entities in my reducers, which means each reducer has a separate entities object. I now realise it makes more sense for one reducer to have all entities in it, then just store IDs (such as currentUser or something) in separate reducers.

This approach makes complete sense for merging in entities from an API response, but I can't work out how I'd change any entity.

For example, where would I do an operation like this?

    case SUBSCRIBER_TOGGLED: {
        let projectSubscriberIDs = cloneDeep(action.payload.project.subscriberIDs);

        let indexIfExists = projectSubscriberIDs.indexOf(action.payload.user.id);

        if(indexIfExists != -1){
            projectSubscriberIDs.splice(indexIfExists, 1);
        }else{
            projectSubscriberIDs.push(action.payload.user.id);
        }

        return {
            ...state,
            entities: {
                ...state.entities,
                projects: {
                    ...state.entities.projects,
                    [action.payload.project.id]: {
                        ...action.payload.project,
                        subscriberIDs: projectSubscriberIDs
                    }
                }
            }
        }
    }

• we can't work this out earlier in an action, as actions can't know what's in state
• we can't do this in a reducer that doesn't contain the relevant entities, as reducers can't/shouldn't access other reducers
• it feels wrong to do all of these in the entities reducer, as it'll become an enormous mess

Anyone have any insights here?

Answer 1

A few thoughts:

• An action creator can know what's in state, as redux-thunk lets you write functions that have access to getState().
• Slice reducers can have access to data that's in other state slices, per the Redux FAQ entry on sharing state between slice reducers.
• There's a lot of other options out there for managing normalized state in Redux besides Normalizr. I personally am a fan of the Redux-ORM library, and have written about it extensively in my "Practical Redux" tutorial series.
• In that series, I've specifically shown an approach for writing "feature reducers" that have access to the entire root state tree, as well as generic logic for updating any entity based on its type and ID.
• Finally, you might also want to look into the immer immutable update library to simplify updating that nested state.