Entity Framework 4 上下文是什么？

Question

我只是想了解其他人在使用EF4时如何管理其上下文的反馈意见。我正在创建一个MVC应用程序，使用（我认为：）单元工作、服务层、存储库、EF4 w/POCO技术。

我的控制器使用服务，使用UOW，然后利用存储库从EF获取POCO。

这个实现方式是否正确？

请看下面的代码，任何反馈都将不胜感激！ 控制器

Public Class MyController
    Function ListCustomers() As ActionResult
        Dim _UOW = New UnitOfWork
        Dim _Service = New CustomerService(_UOW)
        Dim _Model = New CustomersViewModel
        _Model.Customers = _Service.GetCustomers
        _UOW.Dispose()

        Return View(_Model)
    End Function
End Class

工作单元

Public Interface IUnitOfWork
    Property Context As GTGContext
    Sub Committ()

End Interface

Public Class UnitOfWork
    Implements IDisposable, IUnitOfWork

    Public Property Context As Domain.GTGContext Implements IUnitOfWork.Context

    Public Sub New()
        _Context = New GTGContext

    End Sub

    Public Sub Committ() Implements IUnitOfWork.Committ
        _Context.SaveChanges()

    End Sub

#Region "IDisposable Support"

    Private _IsDisposed As Boolean

    Protected Overridable Sub Dispose(ByVal Disposing As Boolean)
        If (Not _IsDisposed) Then
            If (Disposing) Then
                If (_Context IsNot Nothing) Then
                    _Context.Dispose()
                End If
            End If

            'TODO: Free unmanaged resources (unmanaged objects) and override Finalize() below.
        End If

        _IsDisposed = True

    End Sub

    'TODO: Override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
    'Protected Overrides Sub Finalize()
    '    Dispose(False)
    '    MyBase.Finalize()
    'End Sub

    Public Sub Dispose() Implements IDisposable.Dispose
        Dispose(True)
        GC.SuppressFinalize(Me)

    End Sub

#End Region

End Class

服务

Public Class CustomerService
    Private _UOW As IUnitOfWork
    Private _Repo As Repository(Of Customer)

    Public Sub New(UOW As IUnitOfWork)
        _UOW = UOW
        _Repo = New Repository(Of Customer)(_UOW)
    End Sub

    Public Function GetCustoemrs() As IQueryable(Of Customer)
        ' Any Business Logic Here
        Return _Repo.GetCustomers()
    End Function

End Class

仓库

Imports System.Data.Objects

Namespace Repositories
    Public Interface IRepository(Of T As Class)
        ReadOnly Property ObjectSet As IObjectSet(Of T)
        ReadOnly Property UnitOfWork As IUnitOfWork
        Function Query(ByVal Expression As Expressions.Expression(Of Func(Of T, Boolean))) As IQueryable(Of T)
        Function GetFirst(ByVal Expression As Expressions.Expression(Of Func(Of T, Boolean))) As T
        Function GetSingle(ByVal Expression As Expressions.Expression(Of Func(Of T, Boolean))) As T
        Sub Add(ByVal Entity As T)
        Sub Attach(ByVal Entity As T)
        Sub Delete(ByVal Entity As T)
        Sub SaveChanges()

    End Interface

    Public Class Repository(Of T As Class)
        Implements IRepository(Of T)

#Region "Private Members/Properties"

        Private _ObjectSet As IObjectSet(Of T)
        Private ReadOnly Property ObjectSet As System.Data.Objects.IObjectSet(Of T) Implements IRepository(Of T).ObjectSet
            Get
                If (_ObjectSet Is Nothing) Then
                    _ObjectSet = UnitOfWork.Context.CreateObjectSet(Of T)()
                End If
                Return _ObjectSet
            End Get
        End Property

        Private _UnitOfWork As IUnitOfWork
        Private ReadOnly Property UnitOfWork As IUnitOfWork Implements IRepository(Of T).UnitOfWork
            Get
                Return _UnitOfWork
            End Get
        End Property

#End Region

#Region "Constructor(s)"

        Public Sub New(ByVal UnitOfWork As IUnitOfWork)
            If (UnitOfWork Is Nothing) Then
                Throw New ArgumentNullException("UnitOfWork")
            End If
            _UnitOfWork = UnitOfWork

        End Sub

#End Region

#Region "IRepository(Of T)"

        Public Sub Add(ByVal Entity As T) Implements IRepository(Of T).Add
            ObjectSet.AddObject(Entity)

        End Sub

        Public Sub Attach(ByVal Entity As T) Implements IRepository(Of T).Attach
            ObjectSet.Attach(Entity)
            UnitOfWork.Context.ObjectStateManager.ChangeObjectState(Entity, EntityState.Modified)

        End Sub

        Public Sub Delete(ByVal Entity As T) Implements IRepository(Of T).Delete
            ObjectSet.DeleteObject(Entity)

        End Sub

        Public Function GetFirst(ByVal Expression As System.Linq.Expressions.Expression(Of System.Func(Of T, Boolean))) As T Implements IRepository(Of T).GetFirst
            Return ObjectSet.FirstOrDefault(Expression)

        End Function

        Public Function GetSingle(ByVal Expression As System.Linq.Expressions.Expression(Of System.Func(Of T, Boolean))) As T Implements IRepository(Of T).GetSingle
            Return ObjectSet.SingleOrDefault(Expression)

        End Function

        Public Function Query(ByVal Expression As System.Linq.Expressions.Expression(Of System.Func(Of T, Boolean))) As System.Linq.IQueryable(Of T) Implements IRepository(Of T).Query
            Return ObjectSet.Where(Expression)

        End Function

        Public Sub SaveChanges() Implements IRepository(Of T).SaveChanges
            UnitOfWork.Committ()

        End Sub

#End Region

    End Class
End Namespace

- Sam

---

从您的总结来看，这听起来是正确的，我也在使用类似的方法 - 除了您的Committ()方法中的拼写错误;-) - BrokenGlass

Answer 1

让我告诉您，我在StackOverflow上花费了很长时间来思考采取什么方法：）

我决定实现这篇关于管理对象上下文的好文章（请注意修订版允许使用多个上下文）。

然后我实现了像这样的外观：

```html

http://dotnetslackers.com/articles/ado_net/Managing-Entity-Framework-ObjectContext-lifespan-and-scope-in-n-layered-ASP-NET-applications.aspx

```

public class MyEntityFacade : FacadeBase<MyEntities, MyEntity>
{
    public object GetAll()
    {
        return this.ObjectContext.MyEntities.ToList();
    }

    public bool HasChild(int parentId)
    {
        return this.ObjectContext.MyEntityChild.Any(c => c.parentId == parentId);
    }
}

当然，这可能有点老旧，但是它确实很好用！所有的服务层/工作单元/存储库都需要写大量的代码来支持它们（EF4肯定是为了减少代码膨胀而生的！）。每次添加新实体时，你还需要写更多乏味的冗余代码。

使用上述方法，我将所有外观/工作单元支持代码放入一个可重用的类库中，我只需编写与实际执行操作相关的外观代码，它可以与多个上下文一起使用。

对我而言，这很好用......哦，不要因为使用“外观”一词而责备我。我从来没有真正去过学校 ;)

谢谢， Richard

附：祝你周末愉快！

- Richard