How do I log from cache

[dayadam]

        AsyncCachePolicy<TResult> GetCacheOnlyPolicy<TResult, TSerialized>(
            string cacheKey, 
            ICacheItemSerializer<TResult, TSerialized> serializer, 
            Func<TResult, bool> shouldCache, 
            IDistributedCache distributedCache) =>
            Policy.CacheAsync(
                distributedCache.AsAsyncCacheProvider(serializer),
                new ResultTtl<TResult>(result =>
                {
                    //Logger.LogInformation(true, "Result {result}.", result);
                    return shouldCache(result) ? new Ttl(CurrentPolicyOptionRecord.CacheTtl ?? default) : default;
                }),
                _ => cacheKey,
                (context, key) =>
                {
                    Logger.LogDebug(context.ToString());
                    Logger.LogDebug(true, "Cache hit {key}.", key);
                    //Logger.LogDebug(true, "Result being put into the cache: {result}.", result);
                },
                (context, key) =>
                {
                    Logger.LogDebug(context.ToString());
                    Logger.LogDebug(true, "Cache miss {key}.", key);
                    //Logger.LogDebug(true, "Result being put into the cache: {result}.", result);
                },
                (context, key) =>
                {
                    Logger.LogDebug(context.ToString());
                    Logger.LogDebug(true, "Cache put {key}.", key);
                    //Logger.LogDebug(true, "Result being put into the cache: {result}.", result); 
                },
                (context, key, exception) => Logger.LogWarning(true, exception, "Cache error getting {key}.", key),
                (context, key, exception) => Logger.LogWarning(true, exception, "Cache error putting {key}.", key));

How do I log what is being put into or gotten from the cache?

[peter-csala]

• onCachePut

An optional onCachePut delegate allows specific code to be executed (for example for logging), after a value has been put to the cache.

• onCacheGet

An optional onCacheGet delegate allows specific code to be executed (for example for logging), when a value is retrieved from cache.

Here you can see when these above two delegates are being called.

---

Policy.Cache(
      cacheProvider: /* the chosen cache provider */,
      ttl: /* time to live timespan */,
      onCacheGet: (_, key) => Logger.Info("Hit {key}", key),
      onCacheMiss: (_, __) => {},
      onCachePut: (_, key) => Logger.Info("Put {key}", key),
      onCacheGetError: null,
      onCachePutError: null
);

[dayadam]

That just logs the key, not the value

[peter-csala]

cacheProvider.TryGet(key) would retrieve the data from the cache. Either use closure to capture the provider or pass it through the context to the delegates.

[dayadam]

Thank you. Let's say I do that on cache put, would that be what is in the cache before or after the put?

[peter-csala]

@dayadam After the put. See line 56 and 57:

Polly/src/Polly/Caching/CacheEngine.cs

Line 56 in 51044c5

cacheProvider.Put(cacheKey, result, ttl);

Polly/src/Polly/Caching/CacheEngine.cs

Line 57 in 51044c5

onCachePut(context, cacheKey);

[dayadam]

I'm having a really hard time getting the content of the value. When I debug and the type is TResult, I can see headers and there is content from the response availble. I can't access content from type TResult as it's not define and I can't seem to implement a custom class (is this what I need to do somehow?). But once I convert to HTTPResponseMessage the content disappears. How can I access the content of type TResult or convert it without data loss?

[peter-csala]

Sorry, could you please provide a bit more context? Or could you please share the related code fragment?

[peter-csala]

@dayadam

Reading your question after a coffee I think I know what do you want. With C# 9's enhanced pattern matching you can do something like this:

var response = new HttpResponseMessage() { Content = new StringContent("Hello") };

await ProcessGenericResult(response);

async Task ProcessGenericResult<TResult>(TResult response)
{
    if(response is HttpResponseMessage { Content: var content })
    {
        Console.WriteLine(await content.ReadAsStringAsync());
    }
}

So, if the response is an instance of HttpResponseMessage then capture its Content property into a variable called content. Inside the if statement you can easily read content.

I hope it helped.