SwiftUI Firebase -如何查询文档然后更新？

import SwiftUI
import Firebase

struct ContentView: View {
    var body: some View {
        Text("Hello, SwiftUI Firebase!")
            .onAppear {
                // 初始化Firebase
                FirebaseApp.configure()
                
                // 创建Firestore实例
                let db = Firestore.firestore()
                
                // 查询文档
                db.collection("users").whereField("name", isEqualTo: "John")
                    .getDocuments { (snapshot, error) in
                        if let error = error {
                            print("Error getting documents: \(error)")
                        } else {
                            for document in snapshot!.documents {
                                // 更新文档字段
                                let documentRef = db.collection("users").document(document.documentID)
                                documentRef.updateData(["age": 30])
                            }
                        }
                    }
            }
    }
}