Access single item at startup

[batjoc]

First of all thanks for creating this great library 🙏

Similar to the question asked in #17, I was looking into a way to access a single item at startup. My use case is the following: in my app, there are several objects stored (not many, probably 10 at most with some attributes). Now what I want to provide is that when a user opens the app, the last selected object is shown. However I'm running into the problem that Store.items is empty at startup.

I noticed that the discussion was marked as solved, however I think it was mainly based on the speed improvements, not the Store.items being valid at startup right? Is this something you plan to build?

[mergesort]

Hey @batjoc! Apologies but not too sorry for the delay, I've been on vacation and wanted to really give myself a nice break. 🙂

You're right that the first access of Store.items will return [] on startup, that's something I want to improve but I'm honestly not sure how. The issue is that there has to be a default value, and since the initial query of all the persisted items has to take place on the @MainActor, there will be some non-zero initialization time when the Task is dispatched.

I do think I have some potential help for you though. I've been working hard on a 2.0 releases of Boutique and Bodega, and one of the improvements is the ability to have a @StoredValue type, similar to @Store. As the name implies it can store a single value which should be accessible at startup. You can see the code in this commit and even pull it into your project now if you'd like.

I can recommend using the 2.0 branch, I'm going to cut a preview release version in the next day or two. There are some minimal API breaking changes, for the purposes of creating a better overall API. The migration should be very small and I think you'll see it's not hard to implement, the reason it's a preview release and not an official release is only because is I want to document a migration path, new features, and build some walkthroughs to show people how to use Boutique and Bodega.

Hope that helps, if that works lemme know how it goes, and if not lemme know if I can help otherwise!

[mergesort]

Thanks a lot for confirming @batjoc, I should have time to look over this today! Could I ask you to share the code you're testing this with? Most helpful would be the object you're trying to save so I can try to recreate this, but all of the initialized objects and call-sites would be really valuable to me as well.

[batjoc]

Sure, see here: https://github.com/batjoc/Boutique/tree/stored-value-bug. I've added a storedItem to the RichNotesController. Each time you add objects, the first one will be set to the storedItem. Now when you restart the app you will notice that it says there are 0 stored objects.

[mergesort]

Hey @batjoc, I took a look and I'm pretty sure you don't have a fresh store, but why that's the case isn't intuitive and is my fault.

If you don't provide a StorageEngine parameter to both @Stored and @StoredValue they will default to SQLiteStorageEngine(directory: .documents(appendingPath: "Data"))!. In the buggy demo variant of the repo you provided neither the Store in App.Store nor the StoredItem provide a parameter, so what happens is that they're sharing the same underlying database. When you try to decode a value for one or the other, it's going to encounter a value that wasn't saved with the same schema (given @Stored and @StoredValue store their data differently), and thus a key decoding error.

If you change this

extension Store where Item == RichNote {
    static let notesStore = Store<RichNote>(cacheIdentifier: \.id)
}

To this

extension Store where Item == RichNote {
    static let notesStore = Store<RichNote>(
        storage: SQLiteStorageEngine(directory: .defaultStorageDirectory(appendingPath: "Notes"))!,
        cacheIdentifier: \.id
    )
}

Then you'll start to see decoding work again once more once you delete your app (since the database is already corrupted).

---

Now of course this isn't something you should have to worry about, and an immediate fix is to make @StoredValue's default parameter be different than @Stored's default parameter. But the best way I can think of to do this is to have an initializer for @StoredValue that computes a deterministic hash by default (so you don't have to think about StorageEngines at all), and allow you to still provide a parameter if that's what you think is best for your needs.

I'm not sold on anything though and very open to ideas if anyone has suggestions.

[batjoc]

Thanks so much for this @mergesort. I indeed wasn't aware that each store needs a different database. After using core data for such a long time where everything is in one database this never crossed my mind sorry. Thanks again for your great support and this nice new feature in version 2.0!

[mergesort]

Of course, just glad I can help! I've put together a pull request for all of v2.0 (#25) including some updates to @StoredValue and examples of how to use them, the key parameter should now prevent the issue you ran into, plus I added the ability to set default values today. 🙂

There are some merge conflicts I need to address and I'll be making a few more small changes, but I expect none of them should affect your usage, so I think the 2.0 branch is safe for your needs.