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My .NET ICache

24 Aug 2010

UPDATE: I posted the code on github: http://github.com/karlseguin/Metsys.Caching

In my last post on design and testability, some questions were raised about the ICache interface I was using. This is going to be a code heavy post - largely meant to be copy and pasted. If you don't understand it, don't use it.

The API is meant to remove some of the repetition that comes from using a cache, by making use of my very good friends Action<T> and Func<T>.

First, the interface:

using System;
using System.Web.Caching;

public interface ICache
{
    T Get<T>(string key, params object[] keyArgs);

    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, params object[] keyArgs);
    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs);
    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs);

    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, params object[] keyArgs);
    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs);
    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs);
    T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs);


    void Insert(string key, object data, params object[] keyArgs);
    void Insert(string key, object data, DateTime absoluteExpiration, params object[] keyArgs);
    void Insert(string key, object data, TimeSpan slidingExpiration, params object[] keyArgs);
    void Insert(string key, object data, CacheDependency dependencies, params object[] keyArgs);
    void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs);
    void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs);

    void Remove(string key, params object[] keyArgs);

    void RemoveAll();

    int Count();        
}

Next we beef up the System.Web.Caching.Cache class with extension methods so that it can do what we need it to:

using System;
using System.Web.Caching;

public static class CacheExtensions
{
    public static T Get<T>(this Cache cache, string key, params object[] keyArgs)
    {
        return (T)cache.Get(BuildKey(key, keyArgs));
    }

    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, keyArgs);
    }
    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, absoluteExpiration, keyArgs);
    }
    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, slidingExpiration, keyArgs);
    }
    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, dependencies, keyArgs);
    }
    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, keyArgs);
    }
    public static T Fetch<T>(this Cache cache, string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        return cache.Fetch(key, null, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, keyArgs);
    }

    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        var item = (T)cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, keyArgs);
        }
        else if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue(item);
        }
        return item;
    }
    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        var item = cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, absoluteExpiration, keyArgs);
            return (T)item;
        }
        if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue((T)item);
        }
        return (T)item;
    }
    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        var item = (T)cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, slidingExpiration, keyArgs);
        }
        else if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue(item);
        }
        return item;
    }
    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        var item = (T)cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, dependencies, keyArgs);
        }
        else if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue(item);
        }
        return item;
    }
    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        var item = (T)cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, dependencies, absoluteExpiration, slidingExpiration, keyArgs);
        }
        else if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue(item);
        }
        return item;
    }
    public static T Fetch<T>(this Cache cache, string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        var item = (T)cache.Get(BuildKey(key, keyArgs));
        if (item == null)
        {
            item = callIfGetReturnsNull();
            cache.Insert(key, item, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, keyArgs);
        }
        else if (callIfGetReturnsValue != null)
        {
            callIfGetReturnsValue(item);
        }
        return item;
    }

    public static void Insert(this Cache cache, string key, object data, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data);
        }
    }
    public static void Insert(this Cache cache, string key, object data, DateTime absoluteExpiration, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data, null, absoluteExpiration, Cache.NoSlidingExpiration);
        }
    }
    public static void Insert(this Cache cache, string key, object data, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data, null, Cache.NoAbsoluteExpiration, slidingExpiration);
        }
    }
    public static void Insert(this Cache cache, string key, object data, CacheDependency dependencies, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data, dependencies);
        }
    }
    public static void Insert(this Cache cache, string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data, dependencies, absoluteExpiration, slidingExpiration);
        }
    }
    public static void Insert(this Cache cache, string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        if (data != null)
        {
            cache.Insert(BuildKey(key, keyArgs), data, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback);
        }
    }

    public static void Remove(this Cache cache, string key, params object[] keyArgs)
    {
        cache.Remove(BuildKey(key, keyArgs));
    }
    public static void RemoveAll(this Cache cache)
    {
        var enumerator = cache.GetEnumerator();
        while (enumerator.MoveNext())
        {
            cache.Remove((string)enumerator.Key);
        }
    }

    private static string BuildKey(string key, params object[] keyArgs)
    {
        return (keyArgs == null || keyArgs.Length == 0) ? key : string.Format(key, keyArgs);
    }
}

Now we wrap the actual System.Web.Caching.Cache class in a wrapper which implements our interface:

using System;
using System.Web;
using System.Web.Caching;

public sealed class InMemoryCache : ICache
{
    public T Get<T>(string key, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Get<T>(key, keyArgs);            
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, keyArgs);
    }
    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, absoluteExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, slidingExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, dependencies, keyArgs);
    }
    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, keyArgs);
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, keyArgs);
    }
    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, absoluteExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, slidingExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, dependencies, keyArgs);
    }
    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, keyArgs);
    }
    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        return HttpRuntime.Cache.Fetch(key, callIfGetReturnsValue, callIfGetReturnsNull, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, keyArgs);
    }

    public void Insert(string key, object data, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, keyArgs);
    }
    public void Insert(string key, object data, DateTime absoluteExpiration, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, absoluteExpiration, keyArgs);
    }
    public void Insert(string key, object data, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, slidingExpiration, keyArgs);
    }
    public void Insert(string key, object data, CacheDependency dependencies, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, dependencies, keyArgs);
    }
    public void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, dependencies, absoluteExpiration, slidingExpiration, keyArgs);
    }
    public void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        HttpRuntime.Cache.Insert(key, data, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, keyArgs);
    }

    public void Remove(string key, params object[] keyArgs)
    {
        HttpRuntime.Cache.Remove(key, keyArgs);
    }
    public void RemoveAll()
    {
        HttpRuntime.Cache.RemoveAll();
    }

    public int Count()
    {
        return HttpRuntime.Cache.Count;
    }
}

Finally, we need a no-cache solution. This is useful in a number of cases, such as development, and easy testing - when testing, you often don't even need a mock, you just want to circumvent the cache mechanism:

using System;
using System.Web.Caching;

public class NoCache : ICache
{
    public T Get<T>(string key, params object[] keyArgs)
    {
        return default(T);
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        return callIfGetReturnsNull();
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;            
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, DateTime absoluteExpiration, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;
    }

    public T Fetch<T>(string key, Action<T> callIfGetReturnsValue, Func<T> callIfGetReturnsNull, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs)
    {
        var r = callIfGetReturnsNull();
        return r == null ? callIfGetReturnsNull() : r;
    }

    public void Insert(string key, object data, params object[] keyArgs){}
    public void Insert(string key, object data, DateTime absoluteExpiration, params object[] keyArgs) { }
    public void Insert(string key, object data, TimeSpan slidingExpiration, params object[] keyArgs) { }
    public void Insert(string key, object data, CacheDependency dependencies, params object[] keyArgs) { }
    public void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, params object[] keyArgs) { }
    public void Insert(string key, object data, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, params object[] keyArgs) { }

    public void Remove(string key, params object[] keyArgs) { }

    public void RemoveAll() { }

    public int Count()
    {
        return 0;
    }
}

That's it. Here's how you might use it in a test. You can greatly clean up the constraints by encapsulating that in a custom constraint - but I don't want to make it too easy for you.

[Fact]
  public void GetsTheUserFromTheCache()
  {
      var user = new User();
      var userId = new Guid("11c2deee-0794-4874-a581-4a75aa85eca5");
      var cache = Dynamic<ICache>();
      var repository = new UserRepository(cache);
       

      cache.Expect(c => c.Fetch(Arg<string>.Is.Equal("user_{0}"), Arg<Func<User>>.Is.Anything, Arg<DateTime>.Is.Anything, Arg<object[]>.Matches(o => (Guid)o[0] == userId && o.Length == 1)))
          .Return(user);
      ReplayAll();

      Assert.Same(user, repository.GetUser(userId));
      cache.VerifyAllExpectations();
  }

  [Fact]
  public void GetsTheUserFromTheStoreIfNotInTheCache()
  {
      var userId = new Guid("11c2deee-0794-4874-a581-4a75aa85eca5");
      var user = new User{Id = userId, Name = "Goku", IsPowerLevelOver900 = true};
      var repository = new UserRepository(new NoCache());
      SomeTestDbHelper.Insert(user);            
      Assert.Equal(user.Id, repository.GetUser(userId).Id);            
  }

  [Fact]
  public void StoresTheUserInTheCache()
  {
      var userId = new Guid("11c2deee-0794-4874-a581-4a75aa85eca5");
      var user = new User{Id = userId, Name = "Vegeta", IsPowerLevelOver900 = false};
      var cache = new InMemoryCache();
      var repository = new UserRepository(cache);
      
      SomeTestDbHelper.Insert(user);            
      var expected = repository.GetUser(userId);
      Assert.Same(expected, cache.Get<User>("user_{0}", user.Id));
  }
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