[API Proposal]: Add GetAsync to HybridCache

[CoryCharlton]

Background and motivation

There are instances, such as session validation, where a consumer only wants to confirm that an item exists in the cache and not create it. This is not currently (directly) possible with the HybridCache implementation.

API Proposal

namespace Microsoft.Extensions.Caching.Hybrid;

public abstract class HybridCache
{
    public abstract ValueTask<T?> GetAsync<T>(string key, HybridCacheEntryOptions? options = null, CancellationToken cancellationToken = default);
}

API Usage

public async ValueTask<bool> ValidateSession(string sessionId, HybridCache cache) 
{
    var session = cache.GetAsync<Session>(sessionId);
    return (session is not null);
}

Alternative Designs

I can make this work using the existing API but I'm not a fan of my solution so if anyone has a better workaround let me know.

public async ValueTask<T?> GetAsync<T>(string key, HybridCacheEntryOptions? options = null, CancellationToken cancellationToken = default) where T : notnull
{
    try
    {
        return await GetOrCreateAsync<T>(key, _ => throw new CacheMissException(), options, null, cancellationToken);
    }
    catch (CacheMissException)
    {
        return default;
    }
}

More efficient option suggested by @nibdev

public static async Task<(bool Found, T? Result)> TryGetAsync<T>(this HybridCache cache, string key) where T : class
{
    var factoryCalled = false;
    var result = await cache.GetOrCreateAsync(
        key,
        _ =>
        {
            factoryCalled = true;
            return ValueTask.FromResult(default(T));
        },
        new HybridCacheEntryOptions
        {
            Expiration = TimeSpan.Zero,
            LocalCacheExpiration = TimeSpan.Zero,
            Flags = HybridCacheEntryFlags.DisableLocalCacheWrite | HybridCacheEntryFlags.DisableDistributedCacheWrite
        });

    return (!factoryCalled, result);
}

Risks

No response

[ondrej-zoo]

I have another type of issue with not having a simple Get method. I would like to cache the access token so I don't need to obtain it every time I call some API. The problem is that I want to configure the absolute expiration of the cache entry based on the expiration of the token provided by the factory method.
The solution to my problem would be either

• having Get method, or
• having an overload of the GetOrCreate method accepting the delegate to create HybridCacheEntryOptions, something like this Func<CancellationToken, T, HybridCacheEntryOptions>

[nibdev]

I can make this work using the existing API but I'm not a fan of my solution so if anyone has a better workaround let me know.

I don't know if this is better for you but it probably is a bit less expensive as it does not use exceptions. And it could cache null and still would tell you if not found or null was cached

public static async Task<(bool Found, T? Result)> TryGetAsync<T>(this HybridCache cache, string key)
    where T : class
{
    var factoryCalled = false;
    var result = await cache.GetOrCreateAsync(
       key,
       _ =>
       {
           factoryCalled = true;
           return ValueTask.FromResult(default(T));
       },
       new HybridCacheEntryOptions
       {
           Expiration = TimeSpan.Zero,
           LocalCacheExpiration = TimeSpan.Zero,
           Flags = HybridCacheEntryFlags.DisableLocalCacheWrite | HybridCacheEntryFlags.DisableDistributedCacheWrite
       });

    return (!factoryCalled, result);
}

[CoryCharlton]

I don't know if this is better for you but it probably is a bit less expensive as it does not use exceptions. And it could cache null and still would tell you if not found or null was cached

Thanks for the suggestion.

[ThomasBarnekow]

I'd support the first API suggestion. I just replaced my use of IDistributedCache with HybridCache in my solution and found the lack of that API a bit odd, to be honest. While it is possible to implement it ourselves, that shouldn't be necessary.

Apart from the options already discussed in this thread, I also tried to use the HybridCacheEntryFlags.DisableUnderlyingData flag. Based on its documentation, it "Only fetches the value from cache; does not attempt to access the underlying data store." However, if the cache entry does not exist, the following line of code returns null, which is unexpected:

HybridCacheEntryOptions options = new() { Flags = HybridCacheEntryFlags.DisableUnderlyingData };
SomeClass value = await cache.GetOrCreateAsync(someKey, _ => new ValueTask(new SomeClass()), options, ...);

The compiler strongly believes value is non-nullable, so it will complain about null checks, for example. Thus, the proposed API, which returns a ValueTask<T?>, would indeed be very helpful.