如何使用flutter检查Firebase实时数据库的特定节点中是否存在特定的key？

import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_database/firebase_database.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

final databaseReference = FirebaseDatabase.instance.reference();

bool isKeyExists(String node, String key) {
  DatabaseReference nodeRef = databaseReference.child(node);
  DataSnapshot snapshot = await nodeRef.once();
  Map<dynamic, dynamic> values = snapshot.value;
  return values.containsKey(key);
}

bool exists = isKeyExists("节点路径", "要检查的key");
if (exists) {
  print("特定的key存在于特定节点中");
} else {
  print("特定的key不存在于特定节点中");
}