nopCommerce 数据缓存

为了提高一个系统或网站的性能和IO吞吐量，我们一般都会采用缓存技术。当然NopCommerce也不例外，本文我们就来给大家分析一下nop中Cache缓存相关类设计、核心源码及实现原理。

一、Nop.Core.Caching.ICacheManager

Nop首先抽象出了一个缓存存储和读取相关管理接口Nop.Core.Caching.ICacheManager。

1. namespace Nop.Core.Caching
   {
   /// <summary>
   /// Cache manager interface
   /// </summary>
   public interface ICacheManager
   {
   /// <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>
   T Get<T>(string 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>
   void Set(string key, object data, int cacheTime);
   /// <summary>
   /// Gets a value indicating whether the value associated with the specified key is cached
   /// </summary>
   /// <param name="key">key</param>
   /// <returns>Result</returns>
   bool IsSet(string key);
   /// <summary>
   /// Removes the value with the specified key from the cache
   /// </summary>
   /// <param name="key">/key</param>
   void Remove(string key);
   /// <summary>
   /// Removes items by pattern
   /// </summary>
   /// <param name="pattern">pattern</param>
   void RemoveByPattern(string pattern);
   /// <summary>
   /// Clear all cache data
   /// </summary>
   void Clear();
   }
   }
   二、Nop.Core.Caching.MemoryCacheManager
   
   接口ICacheManager具体实现是在类Nop.Core.Caching.MemoryCacheManager：
   
   using System;
   using System.Collections.Generic;
   using System.Runtime.Caching;
   using System.Text.RegularExpressions;
   namespace Nop.Core.Caching
   {
   /// <summary>
   /// Represents a manager for caching between HTTP requests (long term caching)
   /// </summary>
   public partial class MemoryCacheManager : ICacheManager
   {
   protected ObjectCache Cache
   {
   get
   {
   return MemoryCache.Default;
   }
   }
   /// <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 virtual 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 virtual void Set(string key, object data, int cacheTime)
   {
   if (data == null)
   return;
   var policy = new CacheItemPolicy();
   policy.AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(cacheTime);
   Cache.Add(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 virtual 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 virtual void Remove(string key)
   {
   Cache.Remove(key);
   }
   /// <summary>
   /// Removes items by pattern
   /// </summary>
   /// <param name="pattern">pattern</param>
   public virtual 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 virtual void Clear()
   {
   foreach (var item in Cache)
   Remove(item.Key);
   }
   }
   }

可以看到上面Nop的缓存数据是使用的的MemoryCache.Default来存储的，MemoryCache.Default是获取对默认 System.Runtime.Caching.MemoryCache 实例的引用，缓存的默认实例，也就是程序运行的内存中。

Nop除了提供了一个MemoryCacheManager，还有一个Nop.Core.Caching.PerRequestCacheManager类，它提供的是MemoryCacheManager相同的功能，不过它是把数据存在HttpContextBase.Items中，如下：

1. using System;
   using System.Collections;
   using System.Collections.Generic;
   using System.Text.RegularExpressions;
   using System.Web;
   namespace Nop.Core.Caching
   {
   /// <summary>
   /// Represents a manager for caching during an HTTP request (short term caching)
   /// </summary>
   public partial class PerRequestCacheManager : ICacheManager
   {
   private readonly HttpContextBase _context;
   /// <summary>
   /// Ctor
   /// </summary>
   /// <param name="context">Context</param>
   public PerRequestCacheManager(HttpContextBase context)
   {
   this._context = context;
   }
   /// <summary>
   /// Creates a new instance of the NopRequestCache class
   /// </summary>
   protected virtual IDictionary GetItems()
   {
   if (_context != null)
   return _context.Items;
   return null;
   }
   //省略其它代码....
   }
   }

三、缓存接口ICacheManager依赖注入

缓存接口ICacheManager使用了依赖注入，我们在Nop.Web.Framework.DependencyRegistrar类中就能找到对ICacheManager的注册代码：

1. //cache manager
   builder.RegisterType<MemoryCacheManager>().As<ICacheManager>().Named<ICacheManager>("nop_cache_static").SingleInstance();
   builder.RegisterType<PerRequestCacheManager>().As<ICacheManager>().Named<ICacheManager>("nop_cache_per_request").InstancePerLifetimeScope();
   //pass MemoryCacheManager as cacheManager (cache settings between requests)
   builder.RegisterType<ProductTagService>().As<IProductTagService>()
   .WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
   .InstancePerLifetimeScope();
   //pass MemoryCacheManager as cacheManager (cache settings between requests)
   builder.RegisterType<PermissionService>().As<IPermissionService>()
   .WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
   .InstancePerLifetimeScope();
   //pass MemoryCacheManager as cacheManager (cache settings between requests)
   builder.RegisterType<AclService>().As<IAclService>()
   .WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
   .InstancePerLifetimeScope();
   //pass MemoryCacheManager as cacheManager (cache settings between requests)
   builder.RegisterType<PriceCalculationService>().As<IPriceCalculationService>()
   .WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
   .InstancePerLifetimeScope();
   //pass MemoryCacheManager as cacheManager (cache settings between requests)
   builder.RegisterType<CustomerActivityService>().As<ICustomerActivityService>()
   .WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
   .InstancePerLifetimeScope();

上面最开始对接口ICacheManager两实现分别是MemoryCacheManager和PerRequestCacheManager并通过.Named来区分。Autofac高级特性--注册Named命名和Key Service服务

接下来可以配置不同的Service依赖不同的ICacheManager的实现：.WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))或者.WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_per_request"))。

四、具体实例BlogController

下面我们来举例看一下怎么使用这个缓存的。我们就以Nop.Web.Controllers.BlogController的方法BlogTags为例：

1. [ChildActionOnly]
   public ActionResult BlogTags()
   {
   if (!_blogSettings.Enabled)
   return Content("");
   var cacheKey = string.Format(ModelCacheEventConsumer.BLOG_TAGS_MODEL_KEY, _workContext.WorkingLanguage.Id, _storeContext.CurrentStore.Id);
   var cachedModel = _cacheManager.Get(cacheKey, () =>
   {
   var model = new BlogPostTagListModel();
   //get tags
   var tags = _blogService.GetAllBlogPostTags(_storeContext.CurrentStore.Id, _workContext.WorkingLanguage.Id)
   .OrderByDescending(x => x.BlogPostCount)
   .Take(_blogSettings.NumberOfTags)
   .ToList();
   //sorting
   tags = tags.OrderBy(x => x.Name).ToList();
   foreach (var tag in tags)
   model.Tags.Add(new BlogPostTagModel()
   {
   Name = tag.Name,
   BlogPostCount = tag.BlogPostCount
   });
   return model;
   });
   return PartialView(cachedModel);
   }

上面var cachedModel = _cacheManager.Get就是从缓存中读取数据，_cacheManager的Get方法第二个参数是一个lambda表达式，可以传一个方法，这时我们就可以把数据的从数据库中的逻辑放在里面，注意：当第二次请求数据时，如果缓存中有数据，这个Lambda方法是不会执行的。为什么呢？我们可以选中_cacheManager的Get方法按F12进去看这个方法的实现就知道了：

1. using System;
   namespace Nop.Core.Caching
   {
   /// <summary>
   /// Extensions
   /// </summary>
   public static class CacheExtensions
   {
   /// <summary>
   /// Get a cached item. If it‘s not in the cache yet, then load and cache it
   /// </summary>
   /// <typeparam name="T">Type</typeparam>
   /// <param name="cacheManager">Cache manager</param>
   /// <param name="key">Cache key</param>
   /// <param name="acquire">Function to load item if it‘s not in the cache yet</param>
   /// <returns>Cached item</returns>
   public static T Get<T>(this ICacheManager cacheManager, string key, Func<T> acquire)
   {
   return Get(cacheManager, key, 60, acquire);
   }
   /// <summary>
   /// Get a cached item. If it‘s not in the cache yet, then load and cache it
   /// </summary>
   /// <typeparam name="T">Type</typeparam>
   /// <param name="cacheManager">Cache manager</param>
   /// <param name="key">Cache key</param>
   /// <param name="cacheTime">Cache time in minutes (0 - do not cache)</param>
   /// <param name="acquire">Function to load item if it‘s not in the cache yet</param>
   /// <returns>Cached item</returns>
   public static T Get<T>(this ICacheManager cacheManager, string key, int cacheTime, Func<T> acquire)
   {
   if (cacheManager.IsSet(key))
   {
   return cacheManager.Get<T>(key);
   }
   else
   {
   var result = acquire();
   if (cacheTime > 0)
   cacheManager.Set(key, result, cacheTime);
   return result;
   }
   }
   }
   }

可以看到其实上面_cacheManager.Get调用的是类型ICacheManager的一个扩展方法。第二个方法就可以知道，当缓存中有数据直接返回cacheManager.Get<T>(key)，如果没有才进入else分支，执行参数的Lambda表达方式acquire()。

博客园的这篇文章写的不错：http://www.cnblogs.com/gusixing/archive/2012/04/12/2443799.html