Defining a @Query with a variable

[foodstan]

Hi,

I have a NavigationView listing groups, then when tapping on one it switches to a list of messages for that group, and then tapping on a message will load a view of that specific message.

The main @Query finding all groups works fine in MainView, but how do I make a message @Query in the MessageList that only includes messages associated with the group? It won't allow me to pass in the local group variable because it has to be done at init time.

The views:

struct MainView: View {
    @Environment(\.appDatabase) private var appDatabase
    @Query(GroupRequest(ordering: .byName)) private var groups: [Group]

    var body: some View {
      NavigationView {
        List {
          ForEach(groups) { group in
            NavigationLink(destination: MessageList(group: group)) {
              GroupRow(group: group)
            }
          }
        }
      }
   }
}

struct MessageList: View {
    @Environment(\.appDatabase) private var appDatabase
    var group: Group?

    // @Query(MessageRequest(group: group)) private var messages: [Message]
    // error: Cannot use instance member 'group' within property initializer; property initializers run before 'self' is available

    var messages: [Message] {
        do {
            return try appDatabase.databaseReader.read { db in
                return try group!.messages.fetchAll(db)
            }
        } catch {
        }
	return []
    }

    var body: some View {
      List {
        ForEach(messages) { message in
          NavigationLink(destination: MessageView(message: message)) {
            MessageRow(message: message)
          }
        }
      }
    }
}

This works, but it's not a @Query in MessageList so when new messages are inserted, they don't automatically appear in the list like they do from GroupView.

How can I construct a @Query in MessageList that uses the group passed in from the NavigationLink?

[groue]

Hello @foodstan,

Check the "Configuring the Initial Request" section of Adding Parameters to Queryable Types, and the following sections.

In your case, since MainView just wants to initialize MessageList with an "initial request", you'll probably end up with:

struct MessageList: View {
    @Query<MessageRequest> private var messages: [Message]

    init(group: Group) {
        let request = MessageRequest(group: group)
        _messages = Query(request)
    }
}

This will allow MessageList to further control the request if it needs (filter messages, etc), through $messages.

[foodstan]

Thanks!