支持区域的MemoryCache？

Question

我需要添加缓存功能，并找到了一个名为MemoryCache的新类。然而，我发现MemoryCache有点残缺(我需要区域功能)。在其他东西中，我需要添加像ClearAll(区域)这样的东西。作者做了很大的努力来保持这个类没有区域支持，代码如下：

if (regionName != null)
{
throw new NotSupportedException(R.RegionName_not_supported);
}

几乎在每种方法中都能运行。我看不到一种简单的方法来覆盖这个行为。我能想到的添加区域支持的唯一方法是添加一个新类作为MemoryCache的包装器，而不是作为从MemoryCache继承的类。然后在这个新类中创建一个Dictionary，并让每个方法“缓冲”区域调用。听起来又脏又错，但最终...

您是否知道向MemoryCache添加区域的更好方法？

Answer 1

我知道你问这个问题已经很久了，所以这不是对你的一个真正的回答，而是对未来的读者的补充。

我还惊讶地发现，MemoryCache的标准实现不支持区域。这将是非常容易的立即提供。因此，我决定将MemoryCache包装在我自己的简单类中，以提供我经常需要的功能。

我在这里附上我的代码，以便为其他有同样需求的人节省时间！

/// <summary>
/// =================================================================================================================
/// This is a static encapsulation of the Framework provided MemoryCache to make it easier to use.
/// - Keys can be of any type, not just strings.
/// - A typed Get method is provided for the common case where type of retrieved item actually is known.
/// - Exists method is provided.
/// - Except for the Set method with custom policy, some specific Set methods are also provided for convenience.
/// - One SetAbsolute method with remove callback is provided as an example.
///   The Set method can also be used for custom remove/update monitoring.
/// - Domain (or "region") functionality missing in default MemoryCache is provided.
///   This is very useful when adding items with identical keys but belonging to different domains.
///   Example: "Customer" with Id=1, and "Product" with Id=1
/// =================================================================================================================
/// </summary>
public static class MyCache
{
    private const string KeySeparator = "_";
    private const string DefaultDomain = "DefaultDomain";


    private static MemoryCache Cache
    {
        get { return MemoryCache.Default; }
    }

    // -----------------------------------------------------------------------------------------------------------------------------
    // The default instance of the MemoryCache is used.
    // Memory usage can be configured in standard config file.
    // -----------------------------------------------------------------------------------------------------------------------------
    // cacheMemoryLimitMegabytes:   The amount of maximum memory size to be used. Specified in megabytes. 
    //                              The default is zero, which indicates that the MemoryCache instance manages its own memory
    //                              based on the amount of memory that is installed on the computer. 
    // physicalMemoryPercentage:    The percentage of physical memory that the cache can use. It is specified as an integer value from 1 to 100. 
    //                              The default is zero, which indicates that the MemoryCache instance manages its own memory 
    //                              based on the amount of memory that is installed on the computer. 
    // pollingInterval:             The time interval after which the cache implementation compares the current memory load with the 
    //                              absolute and percentage-based memory limits that are set for the cache instance.
    //                              The default is two minutes.
    // -----------------------------------------------------------------------------------------------------------------------------
    //  <configuration>
    //    <system.runtime.caching>
    //      <memoryCache>
    //        <namedCaches>
    //          <add name="default" cacheMemoryLimitMegabytes="0" physicalMemoryPercentage="0" pollingInterval="00:02:00" />
    //        </namedCaches>
    //      </memoryCache>
    //    </system.runtime.caching>
    //  </configuration>
    // -----------------------------------------------------------------------------------------------------------------------------



    /// <summary>
    /// Store an object and let it stay in cache until manually removed.
    /// </summary>
    public static void SetPermanent(string key, object data, string domain = null)
    {
        CacheItemPolicy policy = new CacheItemPolicy { };
        Set(key, data, policy, domain);
    }

    /// <summary>
    /// Store an object and let it stay in cache x minutes from write.
    /// </summary>
    public static void SetAbsolute(string key, object data, double minutes, string domain = null)
    {
        CacheItemPolicy policy = new CacheItemPolicy { AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(minutes) };
        Set(key, data, policy, domain);
    }

    /// <summary>
    /// Store an object and let it stay in cache x minutes from write.
    /// callback is a method to be triggered when item is removed
    /// </summary>
    public static void SetAbsolute(string key, object data, double minutes, CacheEntryRemovedCallback callback, string domain = null)
    {
        CacheItemPolicy policy = new CacheItemPolicy { AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(minutes), RemovedCallback = callback };
        Set(key, data, policy, domain);
    }

    /// <summary>
    /// Store an object and let it stay in cache x minutes from last write or read.
    /// </summary>
    public static void SetSliding(object key, object data, double minutes, string domain = null)
    {
        CacheItemPolicy policy = new CacheItemPolicy { SlidingExpiration = TimeSpan.FromMinutes(minutes) };
        Set(key, data, policy, domain);
    }

    /// <summary>
    /// Store an item and let it stay in cache according to specified policy.
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="data">Object to store</param>
    /// <param name="policy">CacheItemPolicy</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    public static void Set(object key, object data, CacheItemPolicy policy, string domain = null)
    {
        Cache.Add(CombinedKey(key, domain), data, policy);
    }




    /// <summary>
    /// Get typed item from cache.
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    public static T Get<T>(object key, string domain = null)
    {
        return (T)Get(key, domain);
    }

    /// <summary>
    /// Get item from cache.
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    public static object Get(object key, string domain = null)
    {
        return Cache.Get(CombinedKey(key, domain));
    }

    /// <summary>
    /// Check if item exists in cache.
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    public static bool Exists(object key, string domain = null)
    {
        return Cache[CombinedKey(key, domain)] != null;
    }

    /// <summary>
    /// Remove item from cache.
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    public static void Remove(object key, string domain = null)
    {
        Cache.Remove(CombinedKey(key, domain));
    }



    #region Support Methods

    /// <summary>
    /// Parse domain from combinedKey.
    /// This method is exposed publicly because it can be useful in callback methods.
    /// The key property of the callback argument will in our case be the combinedKey.
    /// To be interpreted, it needs to be split into domain and key with these parse methods.
    /// </summary>
    public static string ParseDomain(string combinedKey)
    {
        return combinedKey.Substring(0, combinedKey.IndexOf(KeySeparator));
    }

    /// <summary>
    /// Parse key from combinedKey.
    /// This method is exposed publicly because it can be useful in callback methods.
    /// The key property of the callback argument will in our case be the combinedKey.
    /// To be interpreted, it needs to be split into domain and key with these parse methods.
    /// </summary>
    public static string ParseKey(string combinedKey)
    {
        return combinedKey.Substring(combinedKey.IndexOf(KeySeparator) + KeySeparator.Length);
    }

    /// <summary>
    /// Create a combined key from given values.
    /// The combined key is used when storing and retrieving from the inner MemoryCache instance.
    /// Example: Product_76
    /// </summary>
    /// <param name="key">Key within specified domain</param>
    /// <param name="domain">NULL will fallback to default domain</param>
    private static string CombinedKey(object key, string domain)
    {
        return string.Format("{0}{1}{2}", string.IsNullOrEmpty(domain) ? DefaultDomain : domain, KeySeparator, key);
    }

    #endregion

}

Answer 2

您可以创建多个MemoryCache实例，每个实例对应于数据的每个分区。

http://msdn.microsoft.com/en-us/library/system.runtime.caching.memorycache.aspx：

您可以创建MemoryCache类的多个实例，以便在同一应用程序和同一AppDomain实例

中使用

Answer 3

另一种方法是在MemoryCache周围实现一个包装器，它通过组合键和区域名称来实现区域，例如

public interface ICache 
{
...
    object Get(string key, string regionName = null);
...
}

public class MyCache : ICache
{
    private readonly MemoryCache cache

    public MyCache(MemoryCache cache)
    {
        this.cache = cache.
    }
...
    public object Get(string key, string regionName = null)
    {
        var regionKey = RegionKey(key, regionName);

        return cache.Get(regionKey);
    }   

    private string RegionKey(string key, string regionName)
    {
       // NB Implements region as a suffix, for prefix, swap order in the format
       return string.IsNullOrEmpty(regionName) ? key : string.Format("{0}{1}{2}", key, "::", regionName);
    }
...
}

它并不完美，但它适用于大多数用例。

我已经实现了这一点，并以NuGet包的形式提供：Meerkat.Caching