.Net cache與cache更新

/// <summary>
    /// Represents a MemoryCacheCache
    /// </summary>
    public static class CacheManager
    {
        public static ObjectCache Cache
        {
            get
            {
                return MemoryCache.Default;
            }
        }

        public static bool Contains(string key)
        {
            return Cache.Contains(key);
        }

        /// <summary>
        /// Gets or sets the value associated with the specified key.
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="key">The key of the value to get.</param>
        /// <returns>The value associated with the specified key.</returns>
        public static T Get<T>(string key)
        {
            return (T)Cache[key];
        }

        /// <summary>
        /// Adds the specified key and object to the cache.
        /// </summary>
        /// <param name="key">key</param>
        /// <param name="data">Data</param>
        /// <param name="cacheTime">Cache time</param>
        public static void Set(string key, object data, int cacheTime)
        {
            if (data == null)
                return;

            var policy = new CacheItemPolicy();
            policy.AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(cacheTime);
            Cache.Set(new CacheItem(key, data), policy);
        }/// <summary>
        /// Gets a value indicating whether the value associated with the specified key is cached
        /// </summary>
        /// <param name="key">key</param>
        /// <returns>Result</returns>
        public static bool IsSet(string key)
        {
            return (Cache.Contains(key));
        }

        /// <summary>
        /// Removes the value with the specified key from the cache
        /// </summary>
        /// <param name="key">/key</param>
        public static void Remove(string key)
        {
            Cache.Remove(key);
        }

        /// <summary>
        /// Removes items by pattern
        /// </summary>
        /// <param name="pattern">pattern</param>
        public static void RemoveByPattern(string pattern)
        {
            var regex = new Regex(pattern, RegexOptions.Singleline | RegexOptions.Compiled | RegexOptions.IgnoreCase);
            var keysToRemove = new List<String>();

            foreach (var item in Cache)
                if (regex.IsMatch(item.Key))
                    keysToRemove.Add(item.Key);

            foreach (string key in keysToRemove)
            {
                Remove(key);
            }
        }

        /// <summary>
        /// Clear all cache data
        /// </summary>
        public static void Clear()
        {
            foreach (var item in Cache)
                Remove(item.Key);
        }

        public static void SetWithSql(string key, object data, string connStr, string sql, CacheEntryRemovedCallback callback)
        {
            if (data == null)
                return;

            Cache.Add(new CacheItem(key, data), SqlChangePolicy(connStr, sql, callback));
        }

 private static CacheItemPolicy SqlChangePolicy(string connStr,string sql, CacheEntryRemovedCallback callback)
        {
            SqlDependency.Start(connStr);
            using (SqlConnection conn = new SqlConnection(connStr))
            {
                using (SqlCommand command = new SqlCommand(sql, conn))
                {
                    command.Notification = null;
                    conn.Open();

                    SqlDependency dependency = new SqlDependency(command);
                    dependency.AddCommandDependency(command);

                    SqlChangeMonitor monitor = new SqlChangeMonitor(dependency);

                    CacheItemPolicy policy = new CacheItemPolicy();
                    policy.ChangeMonitors.Add(monitor);

                    command.ExecuteScalar();
                    policy.AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(60*24);
                    policy.RemovedCallback = callback;
                    return policy;
                }
            }
        }