firestore-transactions-in-flutter.dart

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import 'package:cloud_firestore/cloud_firestore.dart';

Future<void> deleteAllDocuments({
    required PostId postId,
    required String inCollection,
  }) {
    return FirebaseFirestore.instance.runTransaction(
      maxAttempts: 3,
      timeout: const Duration(
        seconds: 20,
      ),
      (transaction) async {
        final query = await FirebaseFirestore.instance
            .collection(inCollection)
            .where(
              'post_id',
              isEqualTo: postId,
            )
            .get();
        for (final obj in query.docs) {
          transaction.delete(obj.reference);
        }
      },
    );
  }

Future<void> testIt() async {
  for (final collectionName in const ['likes', 'comments']) {
    await deleteAllDocuments(
      inCollection: collectionName,
      postId: 'postId',
    );
  }
}