1. 引言
很多Web项目，都需要和数据库打交道，典型的就是CRUD（读，写，更新，删除）操作。无论是哪种数据库，Asp.Net MVC 作为后端框架的项目，都有很多操作数据库的类库。最近在一个Web项目中就用到了EntityFramework来存取Sql Server。相信很多人都懂得，如何利用EntityFramework存取数据，所以这方面不做详细的介绍。 今天给大家介绍一种如何利用订阅模式来实现缓存更新。
实现过程主要参照NopCommerce，它是一个开源的电商平台，里面有不少精妙的设计，值得每一个.Net程序员一看。
2. 实现
先来看看未采用Cache的设计，定义一个Service，这个Service主要是利用EntityFramework存取数据。
// 定义简单的数据模型
public class TargetSegment
{
public int Id { get; set; }
public string Segment { get; set; }
}
Service接口和默认实现
public interface ITargetSegmentService
{
TargetSegment GetById(object id);
void Insert(TargetSegment item);
void Update(TargetSegment item);
void Delete(TargetSegment item);
IList<TargetSegment> GetAll();
}
public class TargetSegmentService : ITargetSegmentService
{
private IRepository<TargetSegment> _repository;
public TargetSegmentService(IRepository<TargetSegment> repository)
{
this._repository = repository;
}
public TargetSegment GetById(object id)
{
return this._repository.GetById(id);
}
public void Insert(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Insert(item);
}
public void Update(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Update(item);
}
public void Delete(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Delete(item);
}
public IList<TargetSegment> GetAll()
{
return this._repository.Table.ToList();
}
}
这个实现能够满足基本的需求，但是缺乏优化使得每次当Service调用GetAll 函数的时候，都会从数据库读取所有该类条目。如果没有Update,Create或者Delete每次GetAll返回的数据都是一样的。
因此可以在GetAll这里添加缓存，在Update,Create，Delete更新缓存。
首先我们利用.Net自带的System.Runtime.Caching.ObjectCache 类 定义缓存接口以及简单实现：
public interface ICache : IDisposable
{
T Get<T>(string key);
void Set(string key, object data, int cacheMinutes);
bool IsSet(string key);
void Remove(string key);
void RemoveByPattern(string pattern);
void Clear();
}
public static class CacheExtension
{
public static T GetOrAdd<T>(this ICache cache, string key, int cacheMinutes, Func<T> factory)
{
if (cache.IsSet(key))
{
return cache.Get<T>(key);
}
else
{
var data = factory();
cache.Set(key, data, cacheMinutes);
return data;
}
}
public static void RemoveByPattern(this ICache cache, string pattern, IEnumerable<string> keys)
{
Regex regex = new Regex(pattern, RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.Singleline);
foreach (var target in keys.Where(k=>regex.IsMatch(k)))
{
cache.Remove(target);
}
}
}
public partial class MemoryCache : ICache
{
protected System.Runtime.Caching.ObjectCache Cache
{
get { return System.Runtime.Caching.MemoryCache.Default; }
}
public MemoryCache()
{
}
public T Get<T>(string key)
{
return (T) this.Cache[key];
}
public void Set(string key, object data, int cacheMinutes)
{
if (data == null)
return;
this.Cache.Add(new CacheItem(key, data),
new CacheItemPolicy() {AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(cacheMinutes)});
}
public bool IsSet(string key)
{
return this.Cache.Contains(key);
}
public void Remove(string key)
{
this.Cache.Remove(key);
}
public void RemoveByPattern(string pattern)
{
this.RemoveByPattern(pattern, Cache.Select(item => item.Key));
}
public void Clear()
{
foreach (var item in Cache)
{
this.Remove(item.Key);
}
}
public void Dispose()
{
this.Clear();
}
}
到此为止，已经可以实现缓存跟新了，只要在Insert,Update，Delete 函数里面添加 缓存更新即可。我们进一步利用订阅模式。
订阅模式 一般有三个对象，一个是Subject代表发送给所有订阅者的主题信息。一个是Consumer代表订阅者接受订阅的Subject, 另一个是Publisher代表发送Subject的实现。
这里我们定义几个Subject
// 代表数据删除的Subject
public class EntityDeleted<T> where T: class
{
public T Entity { get; private set; }
public EntityDeleted(T entity)
{
this.Entity = entity;
}
}
public class EntityInserted<T> where T : class
{
public T Entity { get; private set; }
public EntityInserted(T entity)
{
this.Entity = entity;
}
}
public class EntityUpdated<T> where T : class
{
public T Entity { get; private set; }
public EntityUpdated(T entity)
{
this.Entity = entity;
}
}
定义Consumer接口和Cache相关的Consumer实现
public interface IConsumer<T>
{
void HandleEvent(T eventMessage);
}
public class CacheEventConsumer :
IConsumer<EntityInserted<TargetSegment>>,
IConsumer<EntityUpdated<TargetSegment>>,
IConsumer<EntityDeleted<TargetSegment>>
{
private readonly ICache _cache;
public CacheEventConsumer()
{
this._cache = DependencyResolver.Current.GetService(typeof(ICache)) as ICache;
}
public const string AllTargetSegmentPattern = "TargetSegment.All";
public void HandleEvent(EntityInserted<TargetSegment> eventMessage)
{
this._cache.RemoveByPattern(AllTargetSegmentPattern);
}
public void HandleEvent(EntityUpdated<TargetSegment> eventMessage)
{
this._cache.RemoveByPattern(AllTargetSegmentPattern);
}
public void HandleEvent(EntityDeleted<TargetSegment> eventMessage)
{
this._cache.RemoveByPattern(AllTargetSegmentPattern);
}
}
定义publish接口和实现
public interface IEventPublisher
{
void Publish<T>(T eventMessage);
}
public static class EventPublisherExtension
{
public static void EntityInserted<T>(this IEventPublisher eventPublisher, T entity) where T : class
{
eventPublisher.Publish(new EntityInserted<T>(entity));
}
public static void EntityUpdated<T>(this IEventPublisher eventPublisher, T entity) where T : class
{
eventPublisher.Publish(new EntityUpdated<T>(entity));
}
public static void EntityDeleted<T>(this IEventPublisher eventPublisher, T entity) where T : class
{
eventPublisher.Publish(new EntityDeleted<T>(entity));
}
}
public class EventPublisher : IEventPublisher
{
public EventPublisher()
{
}
public void Publish<T>(T eventMessage)
{
var consumers = DependencyResolver.Current.GetServices<IConsumer<T>>();
foreach (var consumer in consumers)
{
this.PublishToConsumer(consumer, eventMessage);
}
}
protected virtual void PublishToConsumer<T>(IConsumer<T> consumer, T eventMessage)
{
try
{
consumer.HandleEvent(eventMessage);
}
catch (Exception exception)
{
throw;
}
}
}
最终的Service多了ICache 和 IEventPublish 两个对象：
public class TargetSegmentService : ITargetSegmentService
{
private IRepository<TargetSegment> _repository;
private ICache _cache;
private IEventPublisher _eventPublisher;
public TargetSegmentService(IRepository<TargetSegment> repository, ICache cache, IEventPublisher eventPublisher)
{
this._repository = repository;
this._cache = cache;
this._eventPublisher = eventPublisher;
}
public TargetSegment GetById(object id)
{
return this._repository.GetById(id);
}
public void Insert(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Insert(item);
this._eventPublisher.EntityInserted(item);
}
public void Update(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Update(item);
this._eventPublisher.EntityUpdated(item);
}
public void Delete(TargetSegment item)
{
if (item == null)
throw new ArgumentNullException("item");
this._repository.Delete(item);
this._eventPublisher.EntityDeleted(item);
}
public IList<TargetSegment> GetAll()
{
return this._cache.GetOrAdd(SnappsCacheEventConsumer.AllTargetSegmentPattern, 60, () =>
{
return this._repository.Table.ToList();
});
}
}
最后通过Unity实现依赖注入
Container.RegisterInstance<ICache>(new MemoryCache(), new ContainerControlledLifetimeManager());
Container.RegisterInstance<IEventPublisher>(new EventPublisher(), new ContainerControlledLifetimeManager());
Container.RegisterType(typeof(IConsumer<>), typeof(CacheEventConsumer), new ContainerControlledLifetimeManager());
3. 总结
这是订阅模式的一种运用，在NopCommerce里面有很多设计模式都运用的非常巧妙，对于EntityFramework的优化远不止这些，以后再给大家分享。
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分类: .Net, Asp.Net MVC