Child view not refreshing for changes on SwiftData model

Question

I have two models like these:

@Model
class Post {
    ...
    @Relationship(inverse: \Comment.post) var comments: [Comment]?
}

@Model
class Comment {
    ...
    var post: Post
}

And in one of my views I use a query like the one below where I show a list of posts and their comments count:

struct PostsList: View {
    @Query var posts: [Post]

    var body: some View {
        List {
            ForEach(posts) { post in
                PostListItem(post: post)
            }
        }
    }
}

struct PostListItem: View {
    @State var post: Post

    var body: some View {
        Text("\(post.title)")
        Text("\(post.comments?.count ?? 0) comments")
    }
}

When I insert a new comment with a given post, and then I go back to the view which shows the list of posts and their comments count, the count is not updated for the post I used unless I relaunch the app.

Is there a way to make SwiftData reload a given query, not when the entities returned changed, but when a related one did?

Answer 1

It turns out the issue was simply in the way I pass the single Post to PostListItem.

Given that I am not an expert in SwiftUI, the only two way I found until now to solve this issue are the following.

Solution 1: Remove the subview PostListItem and render each Post directly in the List.

struct PostsList: View {
    @Query var posts: [Post]

    var body: some View {
        List {
            ForEach(posts) { post in
                Text("\(post.title)")
                Text("\(post.comments?.count ?? 0) comments")
            }
        }
    }
}

Solution 2: Wrap the Post in a view model annotated with @Observable and use it as state in PostListItem.

struct PostsList: View {
    @Query var posts: [Post]

    var body: some View {
        List {
            ForEach(posts) { post in
                PostListItem(model: post)
            }
        }
    }
}

@Observable
class PostListItemModel {
    var post: Post

    init(post: Post) {
        self.post = post
    }
}

struct PostListItem: View {
    var model: PostListItemModel

    var body: some View {
        Text("\(model.post.title)")
        Text("\(model.post.comments?.count ?? 0) comments")
    }
}