一个NHibernate应用的实际例子(A good open source project to learn how to use NHibernate)

此项目名字叫Cuyahoga，是一个CMS。该项目中就使用了NHibernate0.6作为持久层。并且使用了NHibernate0.6新添加的Lazy loading特性，是学习使用NHibernate的上佳例子。 下面是对他的一些评价： - Use the HttpContext to store your NHibernate session facade. This is what I call the HttpContext Local Session pattern 8-)    使用HttpContext .Item来存储NH的Session，亦即使用了HttpRequest--Session的模式 - Access to the session facade is provided by a property get in your overrided ASP.NET page's base class, such as "base.GetCoreRepository.LoadObjectById(..)". This is an alternative to having the repository itself control instantiation such as "CoreRepository.Instance.LoadObjectById(..)"    CoreRepository就是一个数据访问逻辑组件了，对Session进行了管理，并且提供数据持久化的方法。部分代码如下：

     public   class  CoreRepository      {         private ISessionFactory _factory;         private ISession _activeSession;         /**//// <summary>         /// Get the active NHibernate session.         /// </summary>         public ISession ActiveSession         {             get { return this._activeSession; }         }         /**//// <summary>         /// Create a repository for core objects.         /// </summary>         public CoreRepository() : this(false)         {         }         /**//// <summary>         /// Create a repository for core objects.         /// </summary>         /// <param name="openSession">Indicate if the CoreRepository should open a session and keep it in memory.</param>         public CoreRepository(bool openSession)         {             this._factory = SessionFactory.GetInstance().GetNHibernateFactory();             if (openSession)             {                 this._activeSession = this._factory.OpenSession();             }         }         /**//// <summary>         /// Open a NHibernate session.         /// </summary>         public void OpenSession()         {             if (this._activeSession == null || ! this._activeSession.IsOpen)             {                 this._activeSession = this._factory.OpenSession();             }             else             {                 throw new InvalidOperationException("The repository already has an open session");             }         }         /**//// <summary>         /// Flushes the current active NHibernate session.         /// </summary>         public void FlushSession()         {             if (this._activeSession != null && this._activeSession.IsOpen)             {                 this._activeSession.Flush();             }         }         /**//// <summary>         /// Close the active NHibernate session         /// </summary>         public void CloseSession()         {             if (this._activeSession != null && this._activeSession.IsOpen)             {                 this._activeSession.Close();             }         }         Generic methods#region Generic methods         /**//// <summary>         /// Generic method for retrieving single objects by primary key.         /// </summary>         /// <param name="type"></param>         /// <param name="id"></param>         /// <returns></returns>         public object GetObjectById(Type type, int id)         {             if (this._activeSession != null)             {                 return this._activeSession.Load(type, id);             }             else             {                 throw new NullReferenceException("The repository doesn't have an active session");             }         }         /**//// <summary>         /// Get all objects of a given type.         /// </summary>         /// <param name="type"></param>         /// <returns></returns>         public IList GetAll(Type type)         {             return GetAll(type, null);         }         /**//// <summary>         /// Get all objects of a given type and add one or more names of properties to sort on.         /// </summary>         /// <param name="type"></param>         /// <param name="sortProperties"></param>         /// <remarks>Sorting is Ascending order. Construct a specific query/method when the sort order         /// should be different.</remarks>         /// <returns></returns>         public IList GetAll(Type type, params string[] sortProperties)         {             ICriteria crit = this._activeSession.CreateCriteria(type);             if (sortProperties != null)             {                 foreach (string sortProperty in sortProperties)                 {                     crit.AddOrder(Order.Asc(sortProperty));                 }             }             return crit.List();         }         /**//// <summary>         /// Generic method to insert an object.         /// </summary>         /// <param name="obj"></param>         public void SaveObject(object obj)         {             ITransaction trn = this._activeSession.BeginTransaction();             try             {                 // Try to find a UpdateTimestamp property and when found, set it to the current date/time.                 PropertyInfo pi = obj.GetType().GetProperty("UpdateTimestamp");                 if (pi != null)                 {                     pi.SetValue(obj, DateTime.Now, null);                 }                 this._activeSession.Save(obj);                 trn.Commit();             }             catch (Exception ex)             {                 trn.Rollback();                 throw ex;             }         }         /**//// <summary>         /// Generic method to update an object.         /// </summary>         /// <param name="obj"></param>         public void UpdateObject(object obj)         {             ITransaction trn = this._activeSession.BeginTransaction();             try             {                 this._activeSession.Update(obj);                 trn.Commit();             }             catch (Exception ex)             {                 trn.Rollback();                 throw ex;             }         }         /**//// <summary>         /// Delete a specific object. Settings in the mapping file determine if this cascades         /// to related objects.         /// </summary>         /// <param name="obj"></param>         public void DeleteObject(object obj)         {             ITransaction trn = this._activeSession.BeginTransaction();             try             {                 this._activeSession.Delete(obj);                 trn.Commit();             }             catch (Exception ex)             {                 trn.Rollback();                 throw ex;             }         }         /**//// <summary>         /// Attach potentially stale objects to the current NHibernate session. This is required         /// when objects are cached in the ASP.NET cache and they contain lazy loaded members.         /// </summary>         /// <param name="obj"></param>         public void AttachObjectToCurrentSession(object obj)         {             if (this._activeSession != null)             {                 if (this._activeSession.IsOpen)                 {                     this._activeSession.Update(obj);                 }                 else                 {                     throw new InvalidOperationException("The current NHibernate session is not open, so no objects can be attached.");                 }             }             else             {                 throw new NullReferenceException("No active NHibernate session available to attach the object to.");             }         }         /**//// <summary>         /// Mark an object for deletion. Commit the deletion with Session.Flush.         /// </summary>         /// <param name="obj"></param>         public void MarkForDeletion(object obj)         {             this._activeSession.Delete(obj);         }         #endregion            }

- A new NHibernate Open Session at beginning of a web request and close it at the end of the request. This is the "session-per-request" pattern.  - Using a custom IHttpModule called NHSessionModule to provide the handlers for Context_BeginRequest and Context_EndRequest. This is a nice way of automatically wiring up your creation/opening and closing and sessions.   使用了一个HttpModule 来进行Session的存储和获得，代码如下：

using  System; using  System.Web; using  Cuyahoga.Core.Service; namespace  Cuyahoga.Web.Util {     在一个HTTP Request期间管理NHibetnate的Session#region 在一个HTTP Request期间管理NHibetnate的Session     /**//// <summary>     /// Http module that manages the NHibernate sessions during an HTTP Request.     /// </summary>     public class NHSessionModule : IHttpModule     {         /**//// <summary>         /// Default constructor.         /// </summary>         public NHSessionModule()         {         }         public void Init(HttpApplication context)         {             context.BeginRequest += new EventHandler(Context_BeginRequest);             context.EndRequest += new EventHandler(Context_EndRequest);         }         public void Dispose()         {             // Nothing here             }         private void Context_BeginRequest(object sender, EventArgs e)         {             // Create the repository for Core objects and add it to the current HttpContext.             CoreRepository cr = new CoreRepository(true);             HttpContext.Current.Items.Add("CoreRepository", cr);         }         private void Context_EndRequest(object sender, EventArgs e)         {             // Close the NHibernate session.             if (HttpContext.Current.Items["CoreRepository"] != null)             {                 CoreRepository cr = (CoreRepository)HttpContext.Current.Items["CoreRepository"];                 cr.CloseSession();             }         }     }     #endregion }

也就是将session保存到HttpContext.Current.Items中，这样做的好处请看这里。 NHibernate中添加的最重要的特性就是用proxy对延迟加载的支持（包括对集合的和单个object的延迟加载），这也是因为项目中使用了动态代理技术（这要求业务实体的成员需要是virtual的或者实现某个接口）， 这为多表的join带来了性能上的提升。