Caching attribute for method?

Question

Maybe this is dreaming, but is it possible to create an attribute that caches the output of a function (say, in HttpRuntime.Cache) and returns the value from the cache instead of actually executing the function when the parameters to the function are the same?

When I say function, I'm talking about any function, whether it fetches data from a DB, whether it adds two integers, or whether it spits out the content of a file. Any function.

Answer 1

Your best bet is Postsharp. I have no idea if they have what you need, but that's certainly worth checking. By the way, make sure to publish the answer here if you find one.

EDIT: also, googling "postsharp caching" gives some links, like this one: Caching with C#, AOP and PostSharp

UPDATE: I recently stumbled upon this article: Introducing Attribute Based Caching. It describes a postsharp-based library on http://cache.codeplex.com/ if you are still looking for a solution.

Answer 2

I have just the same problem - I have multiply expensive methods in my app and it is necessary for me to cache those results. Some time ago I just copy-pasted similar code but then I decided to factor this logic out of my domain. This is how I did it before:

    static List<News> _topNews = null;
    static DateTime _topNewsLastUpdateTime = DateTime.MinValue;
    const int CacheTime = 5;  // In minutes

    public IList<News> GetTopNews()
    {
        if (_topNewsLastUpdateTime.AddMinutes(CacheTime) < DateTime.Now)
        {
            _topNews = GetList(TopNewsCount);
        }

        return _topNews;
    }

And that is how I can write it now:

    public IList<News> GetTopNews()
    {
        return Cacher.GetFromCache(() => GetList(TopNewsCount));
    }

Cacher - is a simple helper class, here it is:

public static class Cacher
{
    const int CacheTime = 5;  // In minutes

    static Dictionary<long, CacheItem> _cachedResults = new Dictionary<long, CacheItem>();

    public static T GetFromCache<T>(Func<T> action)
    {
        long code = action.GetHashCode();

        if (!_cachedResults.ContainsKey(code))
        {
            lock (_cachedResults)
            {
                if (!_cachedResults.ContainsKey(code))
                {
                    _cachedResults.Add(code, new CacheItem { LastUpdateTime = DateTime.MinValue });
                }
            }
        }

        CacheItem item = _cachedResults[code];
        if (item.LastUpdateTime.AddMinutes(CacheTime) >= DateTime.Now)
        {
            return (T)item.Result;
        }

        T result = action();

        _cachedResults[code] = new CacheItem
        {
            LastUpdateTime = DateTime.Now,
            Result = result
        };

        return result;
    }
}


class CacheItem
{
    public DateTime LastUpdateTime { get; set; }
    public object Result { get; set; }
}

A few words about Cacher. You might notice that I don't use Monitor.Enter() ( lock(...) ) while computing results. It's because copying CacheItem pointer ( return (T)_cachedResults[code].Result; line) is thread safe operation - it is performed by only one stroke. Also it is ok if more than one thread will change this pointer at the same time - they all will be valid.