Flutter Cloudfirestore: how to check whether field exists

My Flutter app uses Firbase Cloudfirestore as its backend. Later I’ll want to add new features to my app which would require new fields in a Firestore document. How can I check whether the field exists in the document and return a default value if it doesn’t?

Stream<List<Car>> streamCars() {
    return _carsCollection.snapshots().map((snapshot) => snapshot.docs.map((document) => Car.fromDocumentSnapshot(document)).toList());
}

static Car fromDocumentSnapshot(DocumentSnapshot snapshot) {
  return Car(
    id: snapshot.id,
    date: snapshot['date'] ?? Timestamp.now(),
    seats: snapshot['seats'] ?? 0,
    newFeature: snapshot['newFeature'] ?? '', // This field does not exist yet and throws error
  );
}

This throws the error:

Bad state: field does not exist within the DocumentSnapshotPlatform

>Solution :

You can do it like so.

newFeature: (snapshot.data() as Map)['newFeature'] ?? ''