Data Caching in ASP.Net

Cached Data Reference Pattern

Whenever an attempt is made to access data from the cache, it should be with the assumption that the data might not be there any more. Thus, the following pattern should be universally applied to your access of cached data. In this case, we're going to assume the object that has been cached is a DataTable.

public DataTable GetCustomers(bool BypassCache)
{
  string cacheKey = "CustomersDataTable";
  object cacheItem = Cache[cacheKey] as DataTable;
  if((BypassCache) || (cacheItem == null))
  {
     cacheItem = GetCustomersFromDataSource();
     Cache.Insert(cacheKey, cacheItem, null,
     DateTime.Now.AddSeconds(GetCacheSecondsFromConfig(cacheKey),
     TimeSpan.Zero);
  }
  return (DataTable)cacheItem;
}

There are several points I'd like to make about this pattern:

• Values, like cacheKey, cacheItem and the cache duration, are defined once and only once.
• The cache can be bypassed as needed—for example, after registering a new customer and redirecting to a list of customers, it would probably be best to bypass the cache and repopulate it with the latest data, which would include the newly inserted customer.
• Cache is only accessed once. This has performance benefits and ensures that NullReferenceExceptions don't occur because the item was present the first time it was checked but had expired before the second check.
• The pattern uses strong type checking. The "as" operator in C# will attempt to cast an object to a type and will simply return null if it fails or if the object is null.
• The duration is stored in a configuration file. All cache dependencies, whether file-based, time-based, or otherwise, should ideally be stored in a configuration file so that changes can be made and performance measured easily. I also recommend that a default cache duration be specified, and that the GetCacheSecondsFromConfig() method uses the default if no duration is specified for the cacheKey being used.