nopCommerce架构分析系列（二）数据Cache

原文（http://www.cnblogs.com/gusixing/archive/2012/04/12/2443799.html）非常感谢作者顾思行的分享！

序言

在很多访问量较大的系统中，尤其在某一项数据访问频次较高时，我们会考虑使用缓存，减少系统和数据库的交互，以达到良好的用户体验。缓存主要有页面缓存和数据缓存。数据缓存的实现有很多方式，有基于memcached的，还有基于.net 4.0数据缓存框架，还有一些其他的实现方式。院子里有 PetterLiumemcached快递上手之C#，有兴趣的可以查看，本文主要讨论的是基于.net 4.0 数据缓存框架.

数据缓存的实现原理

nopCommerce项目中有两类的数据缓存，一个是全局数据缓存MemoryCacheManager，是用.net 4.0数据缓存框架实现的。另一个是页面请求级的数据缓存PerRequestCacheManager是基于HttpContextBase实现的。

1、数据缓存框架是.net 4.0框架中新增的功能，详细了解.net 4.0  的缓存功能请看阿不写的全面认识一下.NET 4.0的缓存功能。

图1 部分缓存框架相关的类

2、基于HttpContextBase页面请求级数据缓存

HttpContextBase 类为抽象类，该类包含的成员与 HttpContext 类相同。 使用 HttpContextBase 类可以创建一些派生类，这些派生类与

HttpContext 类相似，但是可以进行自定义并在 ASP.NET 管道外部使用。 在执行单元测试时，通常使用派生类实现具有自定义行为的成员以实现正在测试的方案，这更容易进行单元测试。HttpContextWrapper 类是从 HttpContextBase 类派生的。 HttpContextWrapper 类用作 HttpContext 类的包装。 在运行时，通常使用 HttpContextWrapper 类的实例调用 HttpContext 对象上的成员。

HttpContext的Items集合是IDictionary键/值对的对象集合，在HttpRequest的生存期中共享。存储成本很高的调用的结果，防止该调用在页面上出现多次。一个HttpRequest中的各个单元需要处理相同或类似的数据。如果数据的生存期只是一个请求，就可以考虑使用HttpContext. Items作为短期的高速缓存。

nopCommerce项目中的缓存

1、缓存的实现

nopCommerce项目缓存类层级图

ICacheManager接口，该接口定义了数据缓存常用的方法。 

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();
    }

CacheExtensions扩展方法对ICacheManager进行扩展。

/// <summary>
    /// Extensions
    /// </summary>
    public static class CacheExtensions
    {
        public static T Get<T>(this ICacheManager cacheManager, string key, Func<T> acquire)
        {
            return Get(cacheManager, key, 60, acquire);
        }

        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 (result != null)
                    cacheManager.Set(key, result, cacheTime);
                return result;
            }
        }
    }

MemoryCacheCache类，使用.net  缓存框架实现数据缓存

/// <summary>
    /// Represents a MemoryCacheCache
    /// </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 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 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 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 void Remove(string key)
        {
            Cache.Remove(key);
        }

        /// <summary>
        /// Removes items by pattern
        /// </summary>
        /// <param name="pattern">pattern</param>
        public 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 void Clear()
        {
            foreach (var item in Cache)
                Remove(item.Key);
        }
    }

PerRequestCacheManager类，实现页面请求级的数据缓存。

/// <summary>
    /// Represents a NopStaticCache
    /// </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 IDictionary GetItems()
        {
            if (_context != null)
                return _context.Items;

            return null;
        }

        /// <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 T Get<T>(string key)
        {
            var items = GetItems();
            if (items == null)
                return default(T);

            return (T)items[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 void Set(string key, object data, int cacheTime)
        {
            var items = GetItems();
            if (items == null)
                return;

            if (data != null)
            {
                if (items.Contains(key))
                    items[key] = data;
                else
                    items.Add(key, data);
            }
        }

        /// <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 bool IsSet(string key)
        {
            var items = GetItems();
            if (items == null)
                return false;
            
            return (items[key] != null);
        }

        /// <summary>
        /// Removes the value with the specified key from the cache
        /// </summary>
        /// <param name="key">/key</param>
        public void Remove(string key)
        {
            var items = GetItems();
            if (items == null)
                return;

            items.Remove(key);
        }

        /// <summary>
        /// Removes items by pattern
        /// </summary>
        /// <param name="pattern">pattern</param>
        public void RemoveByPattern(string pattern)
        {
            var items = GetItems();
            if (items == null)
                return;

            var enumerator = items.GetEnumerator();
            var regex = new Regex(pattern, RegexOptions.Singleline | RegexOptions.Compiled | RegexOptions.IgnoreCase);
            var keysToRemove = new List<String>();
            while (enumerator.MoveNext())
            {
                if (regex.IsMatch(enumerator.Key.ToString()))
                {
                    keysToRemove.Add(enumerator.Key.ToString());
                }
            }

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

        /// <summary>
        /// Clear all cache data
        /// </summary>
        public void Clear()
        {
            var items = GetItems();
            if (items == null)
                return;

            var enumerator = items.GetEnumerator();
            var keysToRemove = new List<String>();
            while (enumerator.MoveNext())
            {
                keysToRemove.Add(enumerator.Key.ToString());
            }

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

NopNullCache类，空的数据缓存类。

/// <summary>
    /// Represents a NopNullCache
    /// </summary>
    public partial class NopNullCache : 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>
        public T Get<T>(string key)
        {
            return default(T);
        }

        /// <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 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>
        public bool IsSet(string key)
        {
            return false;
        }

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

        /// <summary>
        /// Removes items by pattern
        /// </summary>
        /// <param name="pattern">pattern</param>
        public void RemoveByPattern(string pattern)
        {
        }

        /// <summary>
        /// Clear all cache data
        /// </summary>
        public void Clear()
        {
        }
    }

2、缓存的应用

下面是BlogService类中的CRUD，从中我们可以了解到，数据缓存是如何处理的，在数据检索时，直接从缓存取数据，其他方法均根据相关正则表达式移除BlogPost的所有缓存，以避免读取到脏数据。

/// <summary>
        /// Gets a blog post
        /// </summary>
        /// <param name="blogPostId">Blog post identifier</param>
        /// <returns>Blog post</returns>
        public virtual BlogPost GetBlogPostById(int blogPostId)
        {
            if (blogPostId == 0)
                return null;

            string key = string.Format(BLOGPOST_BY_ID_KEY, blogPostId);
            return _cacheManager.Get(key, () =>
            {
                var pv = _blogPostRepository.GetById(blogPostId);
                return pv;
            });
        }

        /// <summary>
        /// Deletes a blog post
        /// </summary>
        /// <param name="blogPost">Blog post</param>
        public virtual void DeleteBlogPost(BlogPost blogPost)
        {
            if (blogPost == null)
                throw new ArgumentNullException("blogPost");

            _blogPostRepository.Delete(blogPost);

            _cacheManager.RemoveByPattern(BLOGPOST_PATTERN_KEY);

            //event notification
            _eventPublisher.EntityDeleted(blogPost);
        }


        /// <summary>
        /// Inserts an blog post
        /// </summary>
        /// <param name="blogPost">Blog post</param>
        public virtual void InsertBlogPost(BlogPost blogPost)
        {
            if (blogPost == null)
                throw new ArgumentNullException("blogPost");

            _blogPostRepository.Insert(blogPost);

            _cacheManager.RemoveByPattern(BLOGPOST_PATTERN_KEY);

            //event notification
            _eventPublisher.EntityInserted(blogPost);
        }

        /// <summary>
        /// Updates the blog post
        /// </summary>
        /// <param name="blogPost">Blog post</param>
        public virtual void UpdateBlogPost(BlogPost blogPost)
        {
            if (blogPost == null)
                throw new ArgumentNullException("blogPost");

            _blogPostRepository.Update(blogPost);

            _cacheManager.RemoveByPattern(BLOGPOST_PATTERN_KEY);

            //event notification
            _eventPublisher.EntityUpdated(blogPost);
        }

下面是nopCommerce中该部分的依赖注入部分：ps：nopCommerce的依赖注入会在以后为大家介绍：）

//HTTP context and other related stuff
            builder.Register(c => 
                //register FakeHttpContext when HttpContext is not available
                HttpContext.Current != null ?
                (new HttpContextWrapper(HttpContext.Current) as HttpContextBase) :
                (new FakeHttpContext("~/") as HttpContextBase))
                .As<HttpContextBase>()
                .InstancePerHttpRequest();
            builder.Register(c => c.Resolve<HttpContextBase>().Request)
                .As<HttpRequestBase>()
                .InstancePerHttpRequest();
            builder.Register(c => c.Resolve<HttpContextBase>().Response)
                .As<HttpResponseBase>()
                .InstancePerHttpRequest();
            builder.Register(c => c.Resolve<HttpContextBase>().Server)
                .As<HttpServerUtilityBase>()
                .InstancePerHttpRequest();
            builder.Register(c => c.Resolve<HttpContextBase>().Session)
                .As<HttpSessionStateBase>()
                .InstancePerHttpRequest();
       //cache manager
            builder.RegisterType<MemoryCacheManager>().As<ICacheManager>().Named<ICacheManager>("nop_cache_static").SingleInstance();
            builder.RegisterType<PerRequestCacheManager>().As<ICacheManager>().Named<ICacheManager>("nop_cache_per_request").InstancePerHttpRequest();

有何改进指出？

在缓存具体实现的时候，除了检索方法，其他的CRUD方法，均删除了所有同类的数据缓存，我们是不是可以这样想，上面的BlogPost肯定是有主键的，我们可以根据主键对缓存里面数据进行相关的操作，而不是在增删改的时候，移除所有的BlogPost缓存。

总结

在我们的系统中，根据需要去判断是否需要去设置缓存，采用何种方式去实现缓存？nopCommerce项目中给我提供了很好的例子，在实际应用可以借鉴其实现方式，增强我们系统的用户体验。

相关资料：

1、为短时间状态存储应用HttpContext.Current.Items

2、全面认识一下.NET 4.0的缓存功能

3、HttpContext是干什么的

4、为什么是HttpContextBase而不是IHttpContext