description

# openCursor method Null safety

Stream<CursorWithValue> openCursor (

1. {dynamic key,
2. KeyRange? range,
3. String? direction,
4. bool? autoAdvance}

)

Creates a stream of cursors over the records in this object store.

The stream must be manually advanced by calling Cursor.next after each item or by specifying autoAdvance to be true.

    var cursors = objectStore.openCursor().listen(
      (cursor) {
        // ...some processing with the cursor
        cursor.next(); // advance onto the next cursor.
      },
      onDone: () {
        // called when there are no more cursors.
        print('all done!');
      });

Asynchronous operations which are not related to the current transaction will cause the transaction to automatically be committed-- all processing must be done synchronously unless they are additional async requests to the current transaction.

## Implementation

    Stream<CursorWithValue> openCursor(
        {key, KeyRange? range, String? direction, bool? autoAdvance}) {
      var key_OR_range = null;
      if (key != null) {
        if (range != null) {
          throw new ArgumentError('Cannot specify both key and range.');
        }
        key_OR_range = key;
      } else {
        key_OR_range = range;
      }

      // TODO: try/catch this and return a stream with an immediate error.
      var request;
      if (direction == null) {
        request = _openCursor(key_OR_range);
      } else {
        request = _openCursor(key_OR_range, direction);
      }
      return _cursorStreamFromResult(request, autoAdvance);
    }