private(set) var _X: SwiftData.Query<C.Element, C> = .init() error

Question

Modified to answer concerns appearing in comments.

Have the following code:

import SwiftUI
import SwiftData

@main
struct Fu: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        //.modelContainer(for: Bar.self)
    }
}

@Model
class Bar{
    var a: String
    var b: String

    init(a: String = "", b: String = "") {
        self.a = a
        self.b = b
    }
}

struct ContentView: View {
    //@Environment(\.modelContext) var modelContext
    //@Query var fu: Bar
    var fu = Bar()
    var body: some View {
        NavigationStack {
            if (fu.a.isEmpty) {
                NavigationLink("Lucy! I'm home.") {
                    StartScreen()
                }
            } else {
                Text("whatever")
            }
        }
    }
}
 
struct StartScreen: View {
    var body: some View {
        Text("Hello, World!")
    }
}

The above compiles and runs. In "ContentView," uncomment the '@Query...' and comment 'var fu = ....' on the next line. The editor shows no error. Now click 'run.' The build fails, but no indicataion in the editor. The issues frame shows 'Element is not a member type of class 'example.Bar' - click on the message and the 'private(set)' line appears beneath the @Query.

Well a @Query gives you an array containing all the Bars in the model container. Which one do you want to be edited by the text field? — Sweeper
– Sweeper, Commented Jul 3 at 1:33
What exactly are you trying to achieve here? And what is the point of the line private(set) var _fu: SwiftData.Query<Bar.Element, Bar> = .init(). If you have no idea what that line means, why is it there? — Andrei G.
– Andrei G., Commented Jul 3 at 3:48
I'm NOT putting it there. It shows up during the build and is not removable. I'm just trying access the persistent data across multiple views. I actually only want one Bar. — Cuse70
– Cuse70, Commented Jul 3 at 3:53
@Cuse70 What do you mean it "shows up". If you remove the line, it just reappears? — Andrei G.
– Andrei G., Commented Jul 3 at 3:57
exactly as stated. The error pops on in the "issues" but no indication in the editor of a problem. .Click on the error and that line appears beneath the Query statement — Cuse70
– Cuse70, Commented Jul 3 at 4:00

Andrei G. · Accepted Answer · 2025-07-03 04:26:48Z

With the code as provided, your XCode should light up like a Xmas tree even before building.

Firstly, a @Query returns all instances of the respective model type, so it forcibly needs to be an array - it cannot just return "one Bar", without the proper filtering syntax.

@Query private var bars: [BarModel] // <- needs to be an array type (and private)

Consequently, if bars is an array, something like bars.a.isEmpty makes no sense, because bars is not an instance of a BarModel.

Secondly, a TextField requires a Binding for its text parameter and @Query does not give you any binding. So the error makes sense, because the approach is simply wrong.

Anyway, here's some working code, to show a basic example of how to use @Query, display views conditionally and insert objects into model context:

import SwiftUI
import SwiftData

@Model
class BarModel {
    var a: String
    var b: String
    
    init(a: String = "", b: String = "") {
        self.a = a
        self.b = b
    }
}

struct FooContentView: View {
    
    //Queries
    @Query private var bars: [BarModel]
    
    //Body
    var body: some View {
        
        VStack {
            
            AddBarView()
            
            if bars.isEmpty {
                EmptyBarsView()
            }
            else {
                ForEach(bars) { bar in
                    Text(bar.a)
                }
            }
        }
        .padding()
    }
}

struct EmptyBarsView: View {
    
    //Body
    var body: some View {
        
        VStack {
            Text("There are no bars to show.")
        }
    }
}

struct AddBarView: View {
    
    //Environment
    @Environment(\.modelContext) private var modelContext

    //State values
    @State private var barName: String = ""
    
    //Body
    var body: some View {
        
            TextField("Add a bar...", text: $barName)
                .onSubmit {
                    let newBar = BarModel(a: barName)
                    modelContext.insert(newBar)
                    try? modelContext.save()
                    
                    //Reset input field
                    barName = ""
                }
                .textFieldStyle(.roundedBorder)
    }
}

#Preview {
    FooContentView()
        .modelContainer(for: BarModel.self, inMemory: true)
}

Thanks. I'll play with it. Used to Futter, and the design concepts are different. I'm assuming singletons are somehow supported. Seems like every example out there assumes arrays.

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