Trouble with Persisting One-to-Many Relationship Data in SwiftData, What am I Missing?

Hi everyone,

I'm new to programming and I've been experimenting with Apple's SwiftData. I've run into an issue I can't seem to resolve.

I'm creating a personal relationship manager app where I have a Relation model and an Interaction model. Relation has a one-to-many relationship with Interaction. I'm using SwiftData's @Model and @Relationship property wrappers to define these models and their relationship. I've taken inspiration from Apple's sample code, that can be found here:

Adopting SwiftData for a Core Data app (WWDC23 Session: "Migrate to SwiftData")

The relevant parts of the models look something like this:

@Model
final class Relation {
    ...
    @Relationship(.cascade, inverse: \Interaction.relation)
    var interactions: [Interaction] = []
    ...
}

@Model
final class Interaction {
    ...
    var relation: Relation?
    ...
}

In my SwiftUI view, I'm adding a new Interaction to a Relation like this:

private func AddItem() {
    withAnimation {
        let newInteraction = Interaction(...)
        modelContext.insert(newInteraction)
        newInteraction.relation = relation
        relation.interactions.append(newInteraction)
    }
}

When I add a new Interaction like this, everything seems to work fine during that app session. I can see the new Interaction in my app's UI. But when I quit the app and relaunch it, the new Interaction is gone. It's as if it was never saved.

I've double-checked my code and as far as I can tell, I'm using SwiftData correctly. My usage aligns with the sample code provided by Apple, and I'm not getting any errors or warnings. I think that this issue is not related to SwiftData being in Beta, because Apple's sample code works perfectly fine.

I have a few questions:

1. Is there something I'm missing about how to properly save models using SwiftData?
2. Is there a specific step or method I need to call to persist the changes to the Relation and Interaction objects?
3. Is there a way to debug what's going wrong when SwiftData attempts to save these changes?

Any help would be greatly appreciated.

Thank you in advance!

Louis