Could you please provide some guidance/documentation for how to use swift-dependencies along with SwiftData?

[bluprince13]

Description

Can swift-dependencies be used along with SwiftData?

Specifically, if I have classes that depend on ModelContext bound to the main actor, then how can I initialise those dependencies?

Example:

class MyClass {
    @Dependency(\.modelContext) private var modelContext

    func save(title: String) {
        let note = Note(title: title, dateCreated: .now)
        modelContext().insert(note)
    }
}

I ran into error:

"Conformance of 'ModelContext' to 'Sendable' is unavailable: contexts cannot be shared across concurrency contexts; this is an error in the Swift 6 language mode"

I'm relatively new to Swift and SwiftData - so do let me know if I'm going about this the wrong way or shouldn't be using swift-dependencies here.

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

No response

Dependencies version information

No response

Destination operating system

No response

Xcode version information

Version 16.3

Swift Compiler version information

[stephencelis]

Dependency values must be Sendable because they can be accessed from anywhere. ModelContext is not, and so you cannot vend one directly from @Dependency.

I'm not super familiar with SwiftData, but it does provide a ModelActor protocol, and actors are sendable, so this could help, but others with more familiarity with SwiftData may be able to provide better ideas.

[bluprince13]

Okay, thank you! I will look into ModelActor and also wait to see if there are other responses.

[bluprince13]

Thought I'd provide a bit more context and some updates after spending a few hours on this today.

Initially, I had set up MyClass using ModelContext as a singleton, but then ran into conflicts when having multiple test suites running tests depending on the same singleton.

I was able to get around the issues by adding a createTestInstance(modelContext: ModelContext) method and using them to instantiate separate objects of MyClass in all my test suites. My tests started passing without any issues. Whilst this confirmed the issues were caused by the singleton, I wasn't happy with the solution as I had to add methods that are now public, but only used for testing.

Therefore, I looked into Dependency Injection frameworks, and swift-dependencies seemed like a simple one. However, at this point, I ran into the problem of the ModelContext not being Sendable. I also tried using https://github.com/hmlongco/Factory and ran into the same issue.

In the end, I ended up not using a Dependency Injection library and instead instantiating the objects in MyApp.swift directly, and passing them along to any descendant classes via SwiftUI's environment as described here.

Whilst this works, I think in the long run, I could end up having to create a lot of objects in MyApp.swift and passing them all along via SwiftUI's environment. This isn't ideal because every time any of the values in the object changes, the view’s body will be re-evaluated, even if the value changed is not a value that is used by this specific view (as described in this article). I can see from the swift-dependencies docs docs that it's possible to specify a minimal interface as the dependency for a view.

Perhaps there are other reasons not to use the environment too, and prefer a dependency injection framework. I'd be interested to learn what they are.

I just need to figure out the right pattern to use it with something that's not Sendable.