I share this simple article to show you some code about a TCache async method. I encountered this exception: Unable to convert a async lambda expression in Func.

Asynchronous lambda with Func

//lambda async expression in func
//the previows signature was :T Get(string cacheKeyName, int cacheTimeOutSeconds, Func<T> func)

string cacheName = "all-tenants-cache-name";
                int cacheTimeOutSeconds = 30;
                List<Tenant> tenants = 
                await new TCacheProvider<List<Tenant>>().Get(
                            cacheName, cacheTimeOutSeconds,
                             async () =>{
                                           //here some asynchronous methods
                                           //please return something here
                                        });

ITCache.cs

using System;
using System.Threading.Tasks;

namespace Custom.TCache.Web
{
    public interface ITCache<T>
    {
        Task<T> Get(string cacheKeyName, int cacheTimeOutSeconds, Func<Task<T>> func);
    }  
}

TCacheProvider.cs

using System;
using System.Threading.Tasks;

namespace Custom.TCache.Web
{
    public class TCacheProvider<T>
    {
        public Task<T> Get(string cacheKeyName, int cacheTimeOutSeconds, Func<Task<T>> func)
        {
            return new TCacheInternal<T>().Get(
                cacheKeyName,cacheTimeOutSeconds,func);
        }
    }
}

TCacheProviderInternal.cs

using System;
using System.Threading.Tasks;
using System.Web;

namespace Custom.TCache.Web
{
    public class TCacheProviderInternal<T> : ITCache<T>
    {
        internal static readonly object Locker = new object();

        public Task<T> Get(string cacheName,int cacheTimeOutSeconds,Func<Task<T>> func)
        {
            var obj = HttpContext.Current.Cache.Get(cacheName);
            if (obj != null)
            {
                return (Task<T>)obj;
            }

            lock (Locker)
            {
                if (obj == null)
                {
                    obj = func();
                    HttpContext.Current.Cache.Insert(cacheName, obj, null,
                        DateTime.Now.Add(new TimeSpan(0, 0, cacheTimeOutSeconds)),
                        TimeSpan.Zero);
                }
                return (Task<T>)obj;
            }
        }

    }
}