EntityFramwork--处理数据并发问题时支持乐观并发，即假定最佳场景(这里是指数据在更新过程中没有发生变化)

 

具体看《Beginning ASP.NET 4.5 Databases》P188-189：

 

 

 

本书源代码下载地址：

http://www.codeplex.com/Download?ProjectName=CommonServiceLocator&DownloadId=45067

 

以一下是截取源代码的实现Unit of work、并发、事务的BaseRepository：

BaseRepository.cs：

1 using System; 2 using System.Collections.Generic; 3 using System.Data; 4 using System.Data.Entity; 5 using System.Data.Entity.Infrastructure; 6 using System.Linq; 7 using System.Text; 8 using System.Threading.Tasks; 9 using System.Transactions;10 using Repository;11 12 namespace DataAccess13 {14     public class s : IDisposable15     {16         protected IUnitOfWork UnitOfWork { get; set; }17         private bool disposed = false;18 19         protected StoreEntities Context20         {21             get { return (EfStoreDataContext)this.UnitOfWork; }22         }23 24         /// 
25         /// .ctor26         /// 
27         /// 28         public BaseRepository(IUnitOfWork unitOfWork)29         {30             if (unitOfWork == null) throw new ArgumentNullException("unitOfWork");31             this.UnitOfWork = unitOfWork;32         }33 34         public void Save()35         {36             try37             {38                 using(var scope = new TransactionScope(TransactionScopeOption.RequiresNew))39                 {40                     this.Context.SaveChanges();41                     scope.Complete();42                 }43             }44             catch (DbUpdateConcurrencyException concurrencyException)45             {46                 concurrencyException.Entries.Single().OriginalValues.SetValues(concurrencyException.Entries.Single().GetDatabaseValues());47                 throw;48             }49         }50 51         protected virtual DbSet
     
       GetDbSet
      
       () where TEntity : class52         {53             return this.Context.Set
       
        ();54         }55 56         protected virtual void SetEntityState(object entity, EntityState entityState)57         {58             this.Context.Entry(entity).State = entityState;59         }60 61         protected virtual void Dispose(bool disposing)62         {63             if (!this.disposed)64             {65                 if (disposing)66                 {67                     this.Context.Dispose();68                 }69             }70             this.disposed = true;71         }72 73         public void Dispose()74         {75             Dispose(true);76             GC.SuppressFinalize(this);77         } 78     }79 }
       
      
     

--------------------------- （一）.事务

38                 using(var scope = new TransactionScope(TransactionScopeOption.RequiresNew))39                 {40                     this.Context.SaveChanges();41                     scope.Complete();42                 }

使用事务的目的：在某个场景中,需要更新多个数据上下文实例，并想要把这些更新放在一个事务中。 2.

--------------- （二）并发

44             catch (DbUpdateConcurrencyException concurrencyException)45             {46                 concurrencyException.Entries.Single().OriginalValues.SetValues(concurrencyException.Entries.Single().GetDatabaseValues());47                 throw;48             }

EF框架处理并发的方式：

方式1：

让客户端决定状态----让项的原始值设置为从数据库中获取的值：

concurrencyException.Entries.Single().OriginalValues.SetValues(concurrencyException.Entries.Single().GetDatabaseValues());

方式2：

让客户端决定状态----用存储中的值刷新新实体值：

concurrencyException.Entries.Single().Reload（）; 方式3： 自定义一种方案，选择合适的选项。 --------------------- （三）工作单元 Unit of work

EF中的Unit Of Work机制

（假设StoreEntities 实例的变量名为contexDb）

contexDb.Entry(Order).State = System.Data.EntityState.Modified; //

------------------------------------------------ 下面代码是设计一个实现了Unit of work机制和Repository模式的具体实现：

56         protected virtual void SetEntityState(object entity, EntityState entityState)57         {58             this.Context.Entry(entity).State = entityState;59         }

this.Context是

19         protected StoreEntities Context20         {21             get { return (EfStoreDataContext)this.UnitOfWork; } 22         }

EfStoreDataContext.cs

1     public class EfStoreDataContext : StoreEntities, IUnitOfWork2     {3         public new void SaveChanges()4         {5             base.SaveChanges();6         }7     }

 

EF生成的访问数据的DbContext

1 namespace DataAccess 2 { 3     using System; 4     using System.Data.Entity; 5     using System.Data.Entity.Infrastructure; 6     using Entities; 7      8     public partial class StoreEntities : DbContext 9     {10         public StoreEntities()11             : base("name=StoreEntities")12         {13         }14     15         protected override void OnModelCreating(DbModelBuilder modelBuilder)16         {17             throw new UnintentionalCodeFirstException();18         }19     20         public DbSet
     
       Contacts { get; set; }21         public DbSet
      
        Orders { get; set; }22     }23 }
      
     

 

IUnitofWork.cs

1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using System.Threading.Tasks; 6  7 namespace Repository 8 { 9     public interface IUnitOfWork10     {11         void SaveChanges();12     }13 }

使用了工作单元 （Unit of work）机制的OrderReposiory:

OrderReposiory.cs:

1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using System.Threading.Tasks; 6 using Entities; 7 using Repository; 8  9 namespace DataAccess.Repositories10 {11     public class OrderRepository : BaseRepository, IOrderRepository12     {13 14         public OrderRepository(IUnitOfWork unitOfWork)15             : base(unitOfWork)16         {17 18         }19 20         public IEnumerable
     
       GetAllOrders()21         {22             return this.GetDbSet
      
       ();23         }24 25         public Order GetByOrderId(int orderId)26         {27             return this.GetDbSet
       
        ().Find(orderId);28         }29 30         public void Create(Order order)31         {32             this.GetDbSet
        
         ().Add(order);33         }34 35         public void Update(Order order)36         {37             this.SetEntityState(order, System.Data.EntityState.Modified);38         }39 40         public void Delete(int orderId)41         {42             var order = this.GetDbSet
         
          ().Find(orderId);43             this.GetDbSet
          
           ().Remove(order);44 }45 }46 }
          
         
        
       
      
     

 

根据上面的设计，这行代码：

37             this.SetEntityState(order, System.Data.EntityState.Modified); 最终调用EF框架生成的

public partial class StoreEntities : DbContext 的方法

contexDb.Entry(Order).State = System.Data.EntityState.Modified; //EF中的Unit Of Work机制

假设StoreEntities 实例的变量名为contexDb