Basic guidance on how to use with TCA

[jaredh159]

Thanks so much for the library, already using it in a prototype and loving it.

I'm having trouble figuring out how I would integrate this library and approach with TCA. I'm certain it's straightforward to do so, but for some reason the mental model of how the pieces would fit together just won't click for me. I looked for a case study involving TCA, but don't see any.

Would you be willing to give just a few sentences, or a few short code snippets of how you would imagine this library being integrated into a reducer-driven TCA app? Just enough to put me on the scent would be great.

Many thanks!

[stephencelis]

When we use observable models in our demos, they mostly map to TCA reducers:

• The view holds onto a store instead of the model,
• It accesses store state instead of model properties, and
• It sends actions to the store instead of invoking model methods

Otherwise things look mostly the same. So you could take the SyncUps demo, which uses observable models, and consider how it would be ported.

But the bottom line is you can use @FetchAll (and @FetchOne and @Fetch) wherever you want, or wherever @Shared properties are held. This includes reducer state, effects, even directly in a view if you want. And you can use @Dependency(\.defaultDatabase) to write to the database.

Let us know if you hit any particular stumbling blocks and we'll see if we can help!

[lukesutton]

I have a similar question, and I've managed to integrate SharingGRDB with TCA, but I'm struggling to find a way to have dynamic queries work.

Specifically, I have defined a @Fetch property on my State, which should load data via a FetchKeyRequest e.g.:

@Fetch(Albums(), animation: .default) var albums = Albums.Value()

Which I then update as required in the reducer:

return .run { _ in 
  state.$albums.load(Albums())
}

The issue I'm having is that I'm not able to call state.$albums.load(...) in my reducer, because the closure passed to .run captures the state variable. I understand why this is an error, but I'm stuck on trying to resolve it.

Do you have any guidance on what I could do in this scenario? Thanks!

[mbrandonw]

The issue I'm having is that I'm not able to call state.$albums.load(...) in my reducer, because the closure passed to .run captures the state variable. I understand why this is an error, but I'm stuck on trying to resolve it.

You can always capture the pieces of state you need in .run:

return .run { [albums = state.$albums] in 
  albums.load(Albums())
}

[lukesutton]

Well… I just learnt something new about Swift! Thank you.

[dominikmayer]

I'm struggling a bit with testing SharingGRDB in the Composable Architecture.

Normally the TestStore would detect changes to properties, even shared ones.

But with a shared database this seems not to work. So I have to assert on the state of the database, which means I could miss a change.

An alternative would be to treat the database as a dependency and create a DatabaseClient similar to, let's say, a FileSystemClient, where I would assert on the overridden test methods.

But then all the @Fetch properties in the reducer would not update as I'm not really interacting with the (in-memory) test database.

What's the best way to test SharingGRDB?