How to extend a StateNotifier with non-model data

[scopendo]

Hi,

I've got a situation where I have a model class Category that can be created on-device at runtime from a template category. I have a corresponding state notifier class CategoryController.

I need to differentiate between whether the category exists on the device or not. At first glance, this might be achieved by the controller holding an AsyncValue<Category>. However, this doesn't allow me to differentiate between an existing or new category, as both would result in an AsyncData value.

An easy "watchable" way to understand whether the category exists would be to extend the Category class with a flag to indicate whether it exists, however, I would prefer to avoid that as that's merging a UI-runtime attribute with the real model attributes.

This leaves me with creating a wrapper class so that I end up with:

class ExtendedCategory {
  const ExtendedCategory(Category category, bool exists);
  final Category category;
  final bool exists;
}

class CategoryController extends StateNotifier<AsyncValue<ExtendedCategory>> {
  ...
  state = AsyncData(ExtendedCategory(category, exists));
  ...
}

I don't like this idea because then using the category values becomes a bit unnatural:

final categoryProvider = StateNotifierProvider<CategoryController, AsyncValue<ExtendedCategory>>(...);
...
final extendedCategory = ref.watch(categoryProvider);
print(extendedCategory.exists);
print(extendedCategory.category);

I think what I really want is a subclass of AsyncData, but I don't believe that is currently possible.

Wondering if anyone has a better approach.

[rrousselGit]

I'm a bit lost. What's the relationship between this "exists" and AsyncData?

AsyncData is purely for having a synchronous representation of a Future/Stream. It's unrelated to business logic

[scopendo]

The controller determines whether the category already exists as an async operation. Post-loading the notifier state should be either a category that already exists or a category that does not already exist.

…

On Sat, 27 Nov 2021, 13:17 Remi Rousselet, ***@***.***> wrote: I'm a bit lost. What's the relationship between this "exists" and AsyncData? AsyncData is purely for having a synchronous representation of a Future/ Stream. It's unrelated to business logic — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#959 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAE6N6TEZINFA77TL3EAGKLUODK6DANCNFSM5I4DAVHQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[rrousselGit]

Right, but why is that the responsibility of Asyncvalue and not category?

[scopendo]

Maybe it's not. I have been thinking that the category is an entity that doesn't need to know whether it's been persisted, however, perhaps it should do. Certainly things fall more neatly into place that way.

…

On Sat, 27 Nov 2021, 14:31 Remi Rousselet, ***@***.***> wrote: Right, but why is that the responsibility of Asyncvalue and not category? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#959 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAE6N6VR34ELMIJ5X2W52M3UODTT5ANCNFSM5I4DAVHQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[scopendo]

To round off this topic, I'm addressing this design question by implementing an overarching "categories controller". This also removes the issue.