ASP.NET

// Contract of a cache
interface ICache
{
    void Add(string key, object toCache);
    object Get(string key);
    void Remove(string key);
}

// Session-based cache for live system
class SessionCache: ICache
{
    private HttpSessionState Session
    {
        get
        {
            if (HttpContext.Current != null)
                HttpSessionState.Current.Session;
            return null;
        }
    }

    private bool IsSessionAvailable
    {
        get { return HttpContext.Current != null; }
    }

    public void Add(string key, object toCache)
    {
        if (!IsSessionAvailable) throw new InvalidOperationException("Session cache is only available within an HttpContext.");
        
        Session[key] = toCache;
    }

    public object Get(string key)
    {
        if (!IsSessionAvailable) throw new InvalidOperationException("Session cache is only available within an HttpContext.");

        object item = Session[key];
        return item;
    }

    public void Remove(string key)
    {
        if (!IsSessionAvailable) throw new InvalidOperationException("Session cache is only available within an HttpContext.");

        Session.Remove(key);
    }
}

// Dictionary based cache for unit testing
class DictionaryCache: ICache
{
    private Dictionary<string,> m_cache;

    private Dictionary<string,> Cache
    {
        get 
        {
            if (m_cache == null)
            {
                Interlocked.CompareExchange(ref m_cache, new Dictionary<string,>(), null);
            }
            return m_cache;
        }
    }

    public void Add(string key, object toCache)
    {        
        Cache.Add(key, toCache);
    }

    public object Get(string key)
    {
        object item = Cache[key];
        return item;
    }

    public void Remove(string key)
    {
        Cache.Remove(key);
    }
}

// Facade that acts as a single access point to cache
static class CacheManager
{
    private static ICache s_cache;

    public static ICache CacheInstance
    {
        private get { return s_cache; }
        set { s_cache = value; }
    }


    public void Add(string key, object toCache)
    {
        CacheInstance.Add(key, toCache);
    }

    public object Get(string key)
    {
        return CacheInstance.Get(key);
    }

    public void Remove(string key)
    {
        CacheInstance.Remove(key);
    }
}

// Globa.asax.cs: Inject cache dependency into CacheManager facade
public class Global: HttpApplication
{
    public void Application_Start(object sender, EventArgs e)
    {
        ICache cache = new SessionCache();
        CacheManager.CacheInstance = cache;
    }
}

// Model object with lazy-loaded, cached data
public class ModelEntity
{
    public object LazyLoadedObject
    {
        object item = CacheManager.Get("LazyLoadedObject");
        if (item == null)
        {
            item = GetLazyLoadedObject();
            CacheManager.Add("LazyLoadedObject", item);
        }

        return item;
    }

    private object GetLazyLoadedObject()
    {
        // TODO: Place retrieval logic here
    }
}

// Unit tests
[TestClass]
public class ModelEntityTests
{
    public void LazyLoadedObject_Get_AlreadyCached()
    {
        ICache cache = new DictionaryCache();
        CacheManager.CurrentCache = cache;
        
        object originalInstance = new object();

        cache.Add("LazyLoadedObject", originalInstance);

        ModelEntity entity = new ModelEntity();
        
        object cachedInstance = entity.LazyLoadedObject;

        Assert.AreEqual(originalInstance, cachedInstance);
    }    
}

billcodes wrote:

how to render a gridview from 2 database tables,all the columns from 1 table and only 1 from another table?