https://docs.cloud.google.com/dotnet/docs/reference/Google.Cloud.Firestore.V1/latest/Google.Cloud.Firestore.V1.StructuredQuery.Types.UnaryFilter.OperandTypeOneofCase
Firestore v1 API - Enum StructuredQuery.Types.UnaryFilter.OperandTypeOneofCase (4.2.0) | .NET...