Flutter Cloudfirestore: how to check whether field exists-CodePudding

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

CodePudding user response：

You can do it like so.

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

CodePudding user response：

static Car fromDocumentSnapshot(DocumentSnapshot snapshot) {
  return Car(
    id: snapshot.id,
    date: snapshot['date'] ?? Timestamp.now(),
    seats: snapshot['seats'] ?? 0,
    newFeature: snapshot['newFeature']==null ?'tjhjhjh': '', // check it if is null will solve the error
  );
}