In addition, a developer can now use post-cache substitution to replace part of the cached content with refreshed content. Post-cache substitution allows an application to use page level caching even if part of the page should be dynamically generated.

For most data-driven Web sites, caching can be a thorny topic, especially when a situation demands the need for caching and the necessity of up to date data. In ASP.NET 1.x, pages could be cached for a length of time and organized by input parameters (querystring or POST parameters):

EXAMPLE:

<%@ outputcache duration="3600" varybyparam="PRodID" %>

The code in Listing 5 caches a page in memory for one hour based on the variable ProdID. The problem that arises in the above example is what to do if relevant business data is updated elsewhere. For example, consider a product catalog page cached by product ID. If information about this product (quantity available or price, for example) is updated from an administrative site, incorrect data is cached and displayed to customers. With the previous version of ASP.NET, the solution to this problem would require either manually removing the page from cache using Response.RemoveOutputCacheItem, or waiting until the duration time expires and allowing the system to update the page automatically.