How to Upload a list of objects to Firestore - firebase

Question

I'm developing flutter app with FireStore.
I have declared a variable 'total' and List of objects to be filled with some data from collection called 'cart', then upload these data to collection called 'orders'
This code grab the data from collection 'cart':
void submitOrder() async {
List<CartItem> products =[];
double total =0;
CartItem temp= CartItem(customerId:'' ,itemId:'' ,id: '', title: '', quantity:0, price: 0);
DatabaseService().cartCollection.getDocuments().then(
(snapshot) => snapshot.documents.forEach((doc) {
temp = CartItem(
customerId: user.uid,
itemId: doc.data['itemId'].toString(),
id: doc.documentID.toString(),
title: doc.data['itemName'].toString(),
quantity: int.tryParse(doc.data['quantity'].toString()) ,
price: double.tryParse( doc.data['price'].toString()));
total += temp.quantity*temp.price;
print(total); /// This print shows accurate total
products.add(temp);
}
),
);
// Send data to setOrderData in db class to set new doc in order collection
DatabaseService().setOrderData(products, total, user.uid, branchId, 'open');
}
method setOrderData in DB class:
// Add Order
Future setOrderData(List<CartItem> cartProducts, double total, String customerId, String branchId, String status ) async {
final timestamp = DateTime.now();
return await orderCollection.document(uid).setData(
{
'customerId': customerId,
'branchId': branchId,
'status': status ,
'amount': total.toString(), //
'dateTime': timestamp.toIso8601String(),
'products': cartProducts.map((cp) => {
'id': cp.id,
'title': cp.title,
'quantity': cp.quantity,
'price': cp.price,
}).toList(),
});
}
data in FireStore shows that products and total are null?
Link to image:
If anyone can help me out I'd be grateful.

Answer 1

I highly recommend using a code formatter on your code, as it makes it much more likely that people can spot problems like the one you're having. When I reformat the first code block you shared, it becomes:
void submitOrder() async {
List<CartItem> products = [];
double total = 0;
CartItem temp = CartItem(
customerId: '', itemId: '', id: '', title: '', quantity: 0, price: 0);
DatabaseService().cartCollection.getDocuments().then(
(snapshot) => snapshot.documents.forEach((doc) {
temp = CartItem(
customerId: user.uid,
itemId: doc.data['itemId'].toString(),
id: doc.documentID.toString(),
title: doc.data['itemName'].toString(),
quantity: int.tryParse(doc.data['quantity'].toString()),
price: double.tryParse(doc.data['price'].toString()));
total += temp.quantity * temp.price;
print(total);
/// This print shows accurate total
products.add(temp);
}),
);
// Send data to setOrderData in db class to set new doc in order collection
DatabaseService().setOrderData(products, total, user.uid, branchId, 'open');
}
An in this format it's immediately clear to me that you're calling setOrderData before any of the products.add(temp) calls have happened.
This is because data is loaded from Firestore asynchronously. Since this may take some time, your main code (including the return) continues so the UI is not blocked. Then when the data is available, your then callback is invoked.
This means that any code that needs the data from Firestore needs to be inside the then callback. So in your case, the solution could be as simple as moving the call to setOrderData to inside the then:
void submitOrder() async {
List<CartItem> products = [];
double total = 0;
CartItem temp = CartItem(
customerId: '', itemId: '', id: '', title: '', quantity: 0, price: 0);
DatabaseService().cartCollection.getDocuments().then(
(snapshot) => snapshot.documents.forEach((doc) {
temp = CartItem(
customerId: user.uid,
itemId: doc.data['itemId'].toString(),
id: doc.documentID.toString(),
title: doc.data['itemName'].toString(),
quantity: int.tryParse(doc.data['quantity'].toString()),
price: double.tryParse(doc.data['price'].toString()));
total += temp.quantity * temp.price;
print(total);
/// This print shows accurate total
products.add(temp);
}),
// Send data to setOrderData in db class to set new doc in order collection
DatabaseService().setOrderData(products, total, user.uid, branchId, 'open');
);
}
So the things to take away from this:
Always format your code, as it makes it easier for you and others to understand the flow and find problems.
Data is loaded from Firestore (and most cloud APIs) asynchronously, and you can only use the data inside the then() callback, or by using await.

Answer 2

The best Practice to solve such an error is to use try and then catch with the await for each function like the below code
void submitOrder() async {
List<CartItem> products = [];
double total = 0;
CartItem temp = CartItem(
customerId: '', itemId: '', id: '', title: '', quantity: 0, price: 0);
try {
await DatabaseService().cartCollection.getDocuments().then(
(snapshot) => snapshot.documents.forEach((doc) {
temp = CartItem(
customerId: user.uid,
itemId: doc.data['itemId'].toString(),
id: doc.documentID.toString(),
title: doc.data['itemName'].toString(),
quantity: int.tryParse(doc.data['quantity'].toString()),
price: double.tryParse(doc.data['price'].toString()));
total += temp.quantity * temp.price;
print(total);
/// This print shows accurate total
products.add(temp);
}),
);
// Send data to setOrderData in db class to set new doc in order collection
await DatabaseService()
.setOrderData(products, total, user.uid, branchId, 'open');
} catch (error) {
print(error);
}
}