Asp Caching

ASP Caching

For Core, ignore everything below this (although System.Runtime.Caching still exists).

install Microsoft.Extensions.Caching.Memory
in your startup .Services.AddMemoryCache()
In classes, get IMemoryCache via ctor injection

Session (HttpSessionState) - per user cache
Application (HttpApplicationState - global cache (all users). DOES NOT EXPIRE.
Cache (on HttpRuntime and HttpContext.Current) - Web.Caching.Cache) - global cache (all users). CAN SET EXPIRY.
ObjectCache (.Net 4, MemoryCache, reference System.Runtime.Caching.dll) -
global cache for asp/non-asp (no out-of-the-box Sql/State providers). CAN SET EXPIRY as absolute datetime or CachePolicy.
Page Output caching - stores rendered HTML and/or uses HTTP caching

HttpContext.Current is not available in WCF services - you can enable the asp pipeline with <serviceHostingEnvironment aspNetCompatibilityEnabled="true" /> (there's nothing equivalent in OperationContext, but you can use MemoryCache).

State Servers

Use Session State service on development machines, because it reminds you to only store ISerializable objects.

The command to setup the SQLServer session provider for a webfarm is:

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Aspnet_regsql.exe -S ServerName -U username -P password -ssadd

Append -sstype p to use database "ASPState" instead of tempdb. MSDN

Output caching

See Quickstarts, MSDN concept - MSDN OutputCache.

<%@ OutputCache Duration="60" VaryByParam="none"%>

You MUST have Duration and either VaryByParam (QueryString) or VaryByControl
For VaryByCustom you must override GetVaryByCustomString
Configure on page, user control or web.config cache profiles. If you reference cached user controls in code-behind, check for null.
In 2.0 you also have the "anti-caching" Substitution control.

No caching:

Response.Cache.SetCacheability(HttpCacheability.NoCache);

Response.Cache.SetNoStore();

Response.Cache.SetExpires(DateTime.Now.AddMinutes(-1));

Cache API

HttpRuntime.Cache==HttpContext.Current.Cache but works (slowly) when HttpContext.Current is null so you can use it in console apps/unit tests.

Cache Cache = HttpRuntime.Cache;

string filepath = HttpContext.Current.Server.MapPath(@"\\serverX\data.xml");

Cache["Key"] = o; //simple "non-expiring"

//file dependency (see also AggregateCacheDependency)

Cache.Insert("Key", o, new CacheDependency(filepath));

//expire at midnight

Cache.Insert("Key", o, null, DateTime.Now.AddDays(1).Date, TimeSpan.Zero);

//sliding expiration for minimum 30 minutes

Cache.Insert("Key", o, null, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(30));

//Cache.Add == Cache.Insert, but Add will not update if it already exists (silently, no exception).

//Cache.Insert has overloads, Cache.Add does not

Cache clearing

There's no Clear method.

public static void ClearCache()
{
    var cacheKeys = new List<string>();
    var enumerator = HttpRuntime.Cache.GetEnumerator();

    while (enumerator.MoveNext())
    {
        cacheKeys.Add(enumerator.Key.ToString());
    }

    foreach (var key in cacheKeys)
    {
        HttpRuntime.Cache.Remove(key);
    }
}

.Net 4 MemoryCache

Very useful for unit testing. Can be extended for database-backed cache, but it can't use ASP.Net's Session/Application providers (state server, SqlServer).

public static object GetCache<T>(string key, Func<T> load)
    where T : class
{
    //get the static "default" cache.
    ObjectCache cache = MemoryCache.Default;
    //you can't store null in the cache
    var value = cache[key] as T;
    if (value == null)
    {
        value = load();
        cache[key] = value;
        // ...or...
        //var policy = new CacheItemPolicy { AbsoluteExpiration = DateTime.Now.AddMinutes(5) };
        //cache.Add(key, value, policy);
    }
    return value;
}