@FetchResults doesn't refresh view when updating related fields

Question

Created Aug ’20

Replies 1

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If I query an entity with a relationship to another entity, and then I update that related entity, the view does not refresh automatically. I'm 'forcing' it now, but that doesn't seem right. What's the right way?

See code sample:

Code Block swiftstruct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @FetchRequest(
        sortDescriptors: [],
        animation: .none)
    private var categories: FetchedResults<Category>
    private func forceRefresh() {
        viewContext.refresh(categories[0], mergeChanges: true)
    }
    var body: some View {
        
        VStack {
            List {
                
                ForEach(categories) { category in
                    
                    Section {
                        Text("\(category.name!)").font(.title)
                    }
                    
                    ForEach(category.items?.allObjects as! [Item]) { item in
                        Button {
                            item.name = "\(UUID())"
                        } label: {
                            Text("\(item.name!)").font(.caption)
                        }
                    }
                }
            }
            
            Divider()
            
            Button {
                forceRefresh()
            } label: {
                Text("Force Refresh").foregroundColor(.blue)
            }
        }
    }
}

Boost

Answer 1

DelawareMathGuy OP

Aug ’20

hi,

when a Category has a to-many relationship with an Item, and you edit an attribute of an Item, the item will do an objectWillChange.send(). but your @FetchRequest setup is only responding to changes to Categories.

one possible suggestion: on line 26 when you change the name of an item, insert a line in advance of the name change (between line 25 and line 26) to tell your View that the content it is displaying needs to be recomputed:

Code Block category.objectWillChange.send()

i think that will work -- but full disclosure: i did not test.

hope that helps,
DMG

BTW: thanks for asking. turns out i had something like this in one of my projects and realized when i read your question that i had the same situation in one case. sure enough -- one piece of a display was not updating after editing the "Items" associated with a "Category." i used essentially the idea above, although the technique was a little different.

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