How to sequentially call the Getx controllers - firebase

Question

My Task is :
I have an list of orders in firebase in users collection ,
I want to get information of those orders which is in orders collection,
And moment a list of order is updated in the firebase users collection.
The orders list should be automatically updated to get the latest information from the orders collection.
But for that i have to wait until list of orders is fetched from the users collection and only then i can query from orders collection about those orders..
I am stuck here,
And i want to actually understand Getx's bindStream , ever(), and observable variables,and Obx() is used in widget , But what if it is normal variable and i want to listen to it's changes ,how to do that, because Obx() can be only used while you use Widget
So far my code:
controllers.dart
UtilityController utilityController = UtilityController.instance;
CartController cartController = CartController.instance;
OrderController orderController = OrderController.instance;
UserModel.dart
class UserModel {
String? uid;
String? email;
String? name;
bool? isAdmin;
String? password;
List<CartItemModel>? cart;
String? token;
List<String>? orders;
UserModel({this.uid, this.email, this.name, this.isAdmin, this.password, this.cart, this.token, this.orders});
UserModel.fromSnapshot(DocumentSnapshot snapshot) {
uid = snapshot.id;
name = snapshot['name'];
token = snapshot['token'];
cart = _convertCartItems(snapshot['cart'] ?? []);
orders = new List<String>.from(snapshot['orders']);
}
List<CartItemModel> _convertCartItems(List cartFomDb) {
List<CartItemModel> _result = [];
if (cartFomDb.length > 0) {
cartFomDb.forEach((element) {
_result.add(CartItemModel.fromMap(element));
});
}
return _result;
}
}
UtilityController.dart
class UtilityController extends GetxController {
static UtilityController instance = Get.find();
Rx<UserModel> userModel = UserModel().obs;
#override
void onReady() {
super.onReady();
getUserType();
userModel.bindStream(listenToUser());
}
Stream<UserModel> listenToUser() {
return FirebaseFirestore.instance
.collection("users")
.doc(FirebaseAuth.instance.currentUser?.uid)
.snapshots()
.map((snapshot) => UserModel.fromSnapshot(snapshot));
}
OrderController.dart
class OrderController extends GetxController {
static OrderController instance = Get.find();
RxList<OrderModel> orders = RxList<OrderModel>([]);
#override
void onReady() {
super.onReady();
orders.bindStream(getAllOrders());
ever(utilityController.userModel, function); --> I am using this , but i know this is not the correct way
}
function(UserModel userModel) {
getAllOrders();
}
Stream<List<OrderModel>> getAllOrders() {
return FirebaseFirestore.instance
.collection("orders")
.where(FieldPath.documentId, whereIn: utilityController.userModel.value.orders)
.snapshots()
.map((query) => query.docs.map((item) => OrderModel.fromMap(item.data(), item.id)).toList());
}
}
The utilityController.userModel.value.orders is null !!! it's not yet loaded, so all the orders are fetched :(
And even if the orders are changed... But new orders are not fetched from the orders collection
How to get over this?

Answer 1

Consider using like this.
class OrderController extends GetxController {
static OrderController instance = Get.find();
final isLoading = true.obs;
final isDone = false.obs;
var orders = OrderModel([]).obs;
#override
void onInit() async {
await listenForOrders();
super.onInit();
}
Future listenForOrders() async {
isLoading.value = true;
isDone.value = false;
Stream<QuerySnapshot> _userOrders;
_userOrders = getAllOrders();
_userOrders.listen((QuerySnapshot query) {
if (query.docs.isNotEmpty) {
query.docs.forEach((element) {
orders.addIf(!orders.contains(element), OrderModel.fromDocumentSnapshot(element));
});
} else {
isDone.value = true;
}
isLoading.value = false;
});
}
Stream<QuerySnapshot> getAllOrders() {
return FirebaseFirestore.instance
.collection("orders")
.where(FieldPath.documentId, whereIn: utilityController.userModel.value.orders)
.snapshots();
}
}

Answer 2

The best approach is to use the worker functions provided by getx controller like:
ever - is called every time the Rx variable emits a new value.
everAll - Much like ever , but it takes a List of Rx values Called every time its variable is changed. That's it.
once - is called only the first time the variable has been changed.