Question

I have a cache method which is

 public TReturn Get<TParam, TReturn>(string cacheId, Func<TParam, TReturn> getItemCallback, TParam argument)
        where TReturn : class
        where TParam : class
    {
        TReturn item = (TReturn)HttpRuntime.Cache.Get(cacheId);
        if (item == null)
        {
            item = getItemCallback(argument);
            HttpContext.Current.Cache.Insert(cacheId, item);
        }
        return item;
    }

and i try to use it and it seem ive got no luck here… normally it should work. I am using it this way.

 public List<LookupParameter> GetAllLookupEntries(string tableContext)
 {
     return _cacheProvider.Get<string,List<LookupParameter>>("", 
         _lookupTableRepository.GetAllLookupEntries(tableContext), "");
 }

It say it can’t convert System.Collections.Generic.List<Pyrosphere.Providers.LookupParameter> to System.Func<string,System.Collections.Generic.List<Pyrosphere.Providers.LookupParameter>>

Any idea ?

Answer 1

The problem is your passing a List<string> as the second parameter and it’s expecting a Func<string, List<string>>. Try passing the second argument as a lambda expression

return _cacheProvider.Get<string,List<LookupParameter>>(
  "", 
  arg => _lookupTableRepository.GetAllLookupEntries(arg), 
  tableContext);

Also it may be a bit simpler if you change your Get function to not take an argument. The argument is provided to the Get method and then immediately passed back to the delegate with nothing else done in between. So the callsite could be much simpler by having it handle the argument directly. For example

public TReturn Get<TReturn>(string cacheId, Func<TReturn> getItemCallback)
    where TReturn : class
{
    TReturn item = (TReturn)HttpRuntime.Cache.Get(cacheId);
    if (item == null)
    {
        item = getItemCallback();
        HttpContext.Current.Cache.Insert(cacheId, item);
    }
    return item;
}


return _cacheProvider.Get<List<LookupParameter>>(
  "", 
  ()=> _lookupTableRepository.GetAllLookupEntries(tableContext));