petshop中的控件缓存与数据缓存

以petshop中的NavigationControl.ascx控件为例，以下的“页”即指“NavigationControl.ascx”控件

页中通过：

设置了页缓存，由于担心数据过期，所以设置了页的依赖项：

DependencyFacade.GetCategoryDependency();

并采用轮询机制定期查看页的依赖项是否过期，如下：

每隔pollTime的时间查看数据库，看看页的依赖项(表)是否有数据更新，如果有更新，那么缓存失效，重新查询数据。

至于配置文件中的：

则是用于数据缓存的缓存过期时间。从以下方法中可以看出，

        /// Method to retrieve and cache category name by its ID
        /// </summary>
        /// <param name="categoryId">Category id</param>
        /// <returns>Category name</returns>
        public static string GetCategoryName(string categoryId) {

            Category category = new Category();
            if (!enableCaching)
                return category.GetCategory(categoryId).Name;

            string cacheKey = string.Format(CATEGORY_NAME_KEY, categoryId);

            // Check if the data exists in the data cache
            string data = (string)HttpRuntime.Cache[cacheKey];//1
            if (data == null) {
                // Caching duration from Web.config
                int cacheDuration = int.Parse(ConfigurationManager.AppSettings["CategoryCacheDuration"]);

                // If the data is not in the cache then fetch the data from the business logic tier
                data = category.GetCategory(categoryId).Name;

                // Create a AggregateCacheDependency object from the factory
                AggregateCacheDependency cd = DependencyFacade.GetCategoryDependency();

                // Store the output in the data cache, and Add the necessary AggregateCacheDependency object
                HttpRuntime.Cache.Add(cacheKey, data, cd, DateTime.Now.AddHours(cacheDuration), Cache.NoSlidingExpiration, CacheItemPriority.High, null);//2
            }

            return data;
        }