每個請求的上下文背景：如何更新實體

Question

我有一個存儲庫類，如下所示。有一種獲取實體對象的方法 - GetPaymentByID。我正在檢索Payment對象並對其PaymentType屬性進行更改。但這並不反映在數據庫中。我知道原因 - SaveContextChanges方法使用新的上下文。我需要用上下文請求的方法。因此，我正在每種方法中創建新的上下文。

在這種情況下，如何修改代碼以成功更新數據庫？

注意：客戶端程序不應該使用ObjectContext，因爲存儲庫可以使用另一個不使用實體框架的存儲庫進行更改。

注意： 「一個DataContext是輕量級的，不貴創建」

namespace MyRepository 
{ 


public class MyPaymentRepository 
{ 
    private string connectionStringVal; 
    public MyPaymentRepository() 
    { 
     SqlConnectionStringBuilder sqlBuilder = new SqlConnectionStringBuilder(); 
     sqlBuilder.DataSource = "."; 
     sqlBuilder.InitialCatalog = "LibraryReservationSystem"; 
     sqlBuilder.IntegratedSecurity = true; 

     // Initialize the EntityConnectionStringBuilder. 
     EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder(); 
     entityBuilder.Provider = "System.Data.SqlClient"; 
     entityBuilder.ProviderConnectionString = sqlBuilder.ToString(); 
     entityBuilder.Metadata = @"res://*/MyEDMtest.csdl|res://*/MyEDMtest.ssdl|res://*/MyEDMtest.msl"; 

     connectionStringVal = entityBuilder.ToString(); 
    } 




    public MyEntityDataModelEDM.Payment GetPaymentByID(int paymentID) 
    { 
     MyEntityDataModelEDM.Payment payment; 
     using (var myObjectContext2 = new MyEntityDataModelEDM.LibraryReservationSystemEntities(connectionStringVal)) 
     { 

      Func<MyEntityDataModelEDM.Payment, bool> predicate = (p => p.PaymentID == paymentID); 
      payment = myObjectContext2.Payments.SingleOrDefault(predicate); 
     } 
     return payment; 
    } 


    public void SaveContextChanges(MyEntityDataModelEDM.Payment paymentEntity) 
    { 
     using (var myObjectContext = new MyEntityDataModelEDM.LibraryReservationSystemEntities(connectionStringVal)) 
     { 
      myObjectContext.SaveChanges(); 
     } 
    } 


} 


} 

客戶

 MyRepository.MyPaymentRepository rep = new MyRepository.MyPaymentRepository(); 

     MyEntityDataModelEDM.Payment p2= rep.GetPaymentByID(1); 
     p2.PaymentType = "TeSSS"; 
     rep.SaveContextChanges(p2); 

READING

1. 添加/安裝和實體狀態：http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx

2. Best way to initialize an entity framework context?

3. Entity Framework 4.1: how to work with per call life time data context?

4. Attaching and detaching entities from context correctly in EF4.1

5. Context lifetime management in repository and unit of work pattern

6. Entity Framework Multiple Object Contexts

7. EF4 - Context.Entry isn't available to change an Entity State

Answer 1

您需要添加對象（如果該數據是新的）或附加（如果該數據被編輯）上下文：

http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx

東西沿着這些路線：

public void SaveContextChanges(MyEntityDataModelEDM.Payment paymentEntity) 
{ 
    using (var myObjectContext = new MyEntityDataModelEDM.LibraryReservationSystemEntities(connectionStringVal)) 
    { 
     // use your own logic for determining a "new" entity 
     myObjectContext.Entry(paymentEntity).State = 
       (paymentEntity.PaymentID == default(int)) ? 
           EntityState.Added : 
           EntityState.Modified; 

     myObjectContext.SaveChanges(); 
    } 
}