Create a Firestore ID in Dart

main.dart

import 'dart:math';

const _characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
const _length = 28;

String createFirestoreId() {
  return List.generate(_length, _randomCharacter).join();
}

String _randomCharacter(_) {
  return _characters[Random.secure().nextInt(_characters.length)];
}

void main() {
  print(createFirestoreId()); // Prints a string like 'UhN7eDazLYe8QNMdtyCVzNMrU1t1'
}

DartPad: https://dartpad.dev/?id=cc1f612f45228bfad5837a19a317d2fc

Alternatively, you can use this hack by Luke Pighetti:

FirebaseStore.instance.rootRef.collection('fake').doc().id;

nanoid2 does this neatly. cloud_firestore also does this, but it is not a public interface.