Feature proposal

Firebase Component: Firestore

Hello,
The Firestore C++ SDK currently supports only the count() method in the firebase::firestore::AggregateQuerySnapshot class but lacks a sum() method (and avg()), which is essential for aggregating numeric fields across documents.

Current State

The public functions of AggregateQuerySnapshot are:

• count()
• is_valid()
• Assignment operators (operator=)
• query()

Reference:

• https://github.com/firebase/firebase-cpp-sdk/blob/main/firestore/src/include/firebase/firestore/aggregate_query_snapshot.h#L109

Flutter SDK Implications

This enhancement would also benefit the Flutter SDK, which relies on the Firestore C++ SDK for Windows platform support. For example, in the FlutterFire plugin, unsupported aggregation types like sum currently result in:

...
      case AggregateType::sum:
        std::cout << "Sum is not supported on C++" << std::endl;
        break;
...

Adding sum() to the C++ SDK would also benefit Flutter developers using Firestore on Windows.

Benefits

Implementing a sum() method would:

1. Provide access to Firestore's aggregation capabilities in the C++ SDK.
2. Support more use cases for C++ and Flutter developers.

Looking forward to hearing thoughts and feedback!
Thanks,