The implementation and default behavior of UpsertEntity differs in C++ compared to other languages

[ahsonkhan]

1. The default value of UpsertEntityOptions is UpsertKind::Update in C++, but it is Merge in other languages.
2. We are calling AddEntity in the exception path for some reason, which the other language SDKs don't do. Why do we do this?

C++ implementation:

azure-sdk-for-cpp/sdk/tables/azure-data-tables/src/table_clients.cpp

Lines 599 to 627 in 384552a

	Azure::Response<Models::UpsertEntityResult> TableClient::UpsertEntity(
	Models::TableEntity const& tableEntity,
	Models::UpsertEntityOptions const& options,
	Core::Context const& context)
	{
	(void)options;
	try
	{
	switch (options.UpsertType)
	{
	case Models::UpsertKind::Merge: {
	auto response = MergeEntity(tableEntity, Models::MergeEntityOptions(options), context);
	return Azure::Response<Models::UpsertEntityResult>(
	Models::UpsertEntityResult(response.Value), std::move(response.RawResponse));
	}
	default: {
	auto response = UpdateEntity(tableEntity, Models::UpdateEntityOptions(options), context);
	return Azure::Response<Models::UpsertEntityResult>(
	Models::UpsertEntityResult(response.Value), std::move(response.RawResponse));
	}
	}
	}
	catch (const Azure::Core::RequestFailedException&)
	{
	auto response = AddEntity(tableEntity, Models::AddEntityOptions(options), context);
	return Azure::Response<Models::UpsertEntityResult>(
	Models::UpsertEntityResult(response.Value), std::move(response.RawResponse));
	}
	}

P.S. The (void)options line should be removed (on line 604), since the options are being used here.

.NET implementation:
https://github.com/Azure/azure-sdk-for-net/blob/4e1173308d32f0413788359a87376e673f2ab15b/sdk/tables/Azure.Data.Tables/src/TableClient.cs#L818-L856

GoLang implementation:
https://github.com/Azure/azure-sdk-for-go/blob/3ebd0d439f9d8aa06a0764a60892a8001b997a34/sdk/data/aztables/client.go#L420-L478

cc @jhendrixMSFT, @christothes

[gearama]

works as expected

[ahsonkhan]

There's a behavioral difference, and our SDKs need to be:

1. Idiomatic to the language.
2. Consistent across languages where (1) isn't lost.

That's written in our design guidelines:
https://azure.github.io/azure-sdk/cpp_introduction.html#cpp-principles

Client libraries should be consistent within the language, consistent with the service and consistent between all target languages. In cases of conflict, consistency within the language is the highest priority and consistency between all target languages is the lowest priority.