Getting data from Realtime Database with a conditional statement - flutter

Question

how I can show DeliveryBoys in a specific location, in my realtime database I have a value that I need to compare drivers with which is "City" I would like to have all DeliveryBoys that are in a specific city. How can I do that? Using flutter
Am only able to get all drivers without a conditional statement
**This is my Function that i want to modify **
retrieveOnlineDriversInformation(List onlineNearestDriversList) async {
DatabaseReference ref =
FirebaseDatabase.instance.ref().child("DeliveryBoys");
for (int i = 0; i < onlineNearestDriversList.length; i++) {
await ref
.child(onlineNearestDriversList[i].driverId.toString())
.once()
.then((dataSnapshot) {
var driverKeyInfo = dataSnapshot.snapshot.value;
dList.add(driverKeyInfo);
});
}
}
Database Structure

Answer 1

Based on your responses and as far as I can see, you don't need the loop where you have it. Therefore, I am going to ignore it and simply show you the code that will return the list of driver ids of all drivers for city 'Lusaka'.
Future<List<String>> retrieveOnlineDriversInformation() async {
final driverIds = <String>[];
DatabaseReference ref = FirebaseDatabase.instance.ref().child("drivers");
try {
await ref.orderByChild("city")
.equalTo("Lusaka")
.once()
.then(
(event) {
if (event.snapshot.value != null) {
final driverListData =
Map<String, dynamic>.from(event.snapshot.value! as Map);
driverListData.forEach((key, value) {
driverIds.add(key);
});
}
},
} on FirebaseException catch (error, stackTrace) {
// < Some code here to print database error details or otherwise deal with it >
} catch (error, stackTrace) {
// < Some code here to print other error details or otherwise deal with it >
}
return driverIds;
}
You could instead modify this to just return the Map 'driverListData' which contains each driver's id and associated driver data.
A couple of other points:
You don't stick to a standard naming convention for your database node and field names. I suggest that you always use lowerCamelCase as the standard (so for example, change DriverLicense to driverLicense) as it will match what you typically name the variables within the Flutter/Dart code.
You don't need to hold the driver id as a separate field in the driver node. It is a duplicate (and therefore wastes space on the database) of the driver record key, which is already accessible to you.
As you see, you should always wrap your database call logic in a try / catch clauses in order to handle any errors that the call to the database may return. There are specific exceptions that can be tested for with the on clause.