如何使用Entity框架和存储库模式处理对象上下文？

Question

我在我的应用程序中使用Entity Framework 4.0（VS 2010，VB.NET），我试图以正确的方式执行此操作。 我的代码如下所示：

Public Interface ICustomerRepository
  Function GetAll(ByVal preferance As String) As IEnumerable(Of Customer)
End Interface

接口的实现：

Public Class CustomerRepository

    Implements ICustomerRepository

    Protected objectSet As IObjectSet(Of Customer)

    Public Sub New(ByVal context As ObjectContext)
        Me.objectSet = context.CreateObjectSet(Of Customer)()
    End Sub

    Public Function GetAll(ByVal preferance As String) As
          System.Collections.Generic.IEnumerable(Of Customer) Implements    
          ICustomerRepository.GetAll

          Return Me.objectSet.Where(Function(p) p.preferance = preferance).ToArray
     End Function
End Class

Public Interface IUnitOfWork
   ReadOnly Property Customers() As ICustomerRepository
   Sub Commit()
End Interface

Public Class UnitOfWork
    Implements IUnitOfWork

    Private ReadOnly context As ObjectContext
    Private m_customers As ICustomerRepository


    Public Sub New(ByVal context As ObjectContext)
       If context Is Nothing Then
         Throw New ArgumentNullException("context wasn't supplied")
       End If
       Me.context = context
     End Sub

  Public ReadOnly Property Customers() As ICustomerRepository Implements   
      IUnitOfWork.Customers

    Get
        If Me.m_customers Is Nothing Then
            Me.m_customers = New CustomerRepository(Me.context)
        End If
        Return Me.m_customer
    End Get
   End Property


   Public Sub Commit() Implements IUnitOfWork.Commit
     Me.context.SaveChanges()
   End Sub
End Class

当我想在我的业务层中使用它时：

Using context As New MyDatabseEntities()
Dim uow As New UnitOfWork(context)

For Each customer In uow.Customer.GetAll()
    Console.WriteLine(customer.Name)
Next
End Using

我有多个存储库，Customer只是一个（举个例子）。

我不明白......当我编写使用context as New MyDatabseEntities（）时，这不是对DAL层的依赖吗？

什么是更好的解决方案？

我的存储库是属于DAL还是属于BLL？

在我的CustomerRepository类中使用受保护的objectSet作为IObjectSet（Of Customer）是否可以，或者我不应该使用Of Customer？

提前致谢！