HybridCache support for Tuples

[mrazvanalex]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I've been trying to implement a system based on eTag to return a 304 in case the existing resource has not changed in the Database.

I have a HybridCache instance working alongside this ETag in the API layer. When returning a tuple ( obj, string ) from the cache, they are returned as null, even if values are attributed in the service call. Provided sample code:

var tags = new List<string> { "test" };
var entryOptions = new HybridCacheEntryOptions
{
    Expiration = TimeSpan.FromMinutes(1),
    LocalCacheExpiration = TimeSpan.FromMinutes(1)
};

var clientETag = httpContext.Request.Headers["If-None-Match"].FirstOrDefault();
var  (result, eTag) = await _cache.GetOrCreateAsync($"identifier", async get =>
{
    var (result, eTag) = await _companyService.GetPaginatedBillsAasync(companyId, filter, clientETag); // values retrieved from service 
    return  (result, eTag); // values are attributed.
}, entryOptions, tags); // values are still shown in breakpoints
// After reaching this point, result and eTag are now null.

if (result == null) // Here result is always null. 
{
    return Results.StatusCode(304); 
}

Describe the solution you'd like

I expect the tuple to retain it's value after the Func has finished it's execution.

Additional context

[konjac]

Actually, Tuple is working but ValueTuple is not. A workaround is to use Tuple.Create(result, eTag) explicitly.

The problem is DefaultHybridCache serializes/deserializes the cache item using System.Text.Json.Serializer with JsonSerializerOptions.Default. The default serializer option does not support fields in ValueTuple. Tuple stores items as properties, so it can work.

var valueTuple = ValueTuple.Create<int, string>(123, "string");
var tuple = Tuple.Create<int, string>(123, "string");
var optionsIncludeFields = new JsonSerializerOptions()
{
	IncludeFields = true
};
string tupleJsonString = JsonSerializer.Serialize(tuple, JsonSerializerOptions.Default);
string valueTupleJsonString = JsonSerializer.Serialize(valueTuple, JsonSerializerOptions.Default);
string valueTupleJsonStringIncludeFields = JsonSerializer.Serialize(valueTuple, optionsIncludeFields);
Console.WriteLine("Vuple      serialized with default:\t{0}", tupleJsonString);
Console.WriteLine("ValueTuple serialized with default:\t{0}", valueTupleJsonString);
Console.WriteLine("ValueTuple serialized with fields: \t{0}", valueTupleJsonStringIncludeFields);

//Output
//Tuple      serialized with default:    {"Item1":123,"Item2":"string"}
//ValueTuple serialized with default:    {}
//ValueTuple serialized with fields:     {"Item1":123,"Item2":"string"}

[mgravell]

In addition to #5827, I propose that we detect value-tuples and use a shared field-enabled options instance; we can't do that globally without changing behaviour, but I think it is the correct choice for value-tuples.