Question

I have a MVC app using the UnitOfWork, Service Layer, Repository Pattern and EF4 as the ORM.

My question is does this (UnitOfWork) having a property that is the Context to the EF tightly couple my layers?

Unit Of Work

Public Interface IUnitOfWork
    Inherits IDisposable

    Property Context As GTGContext
    Sub Commit()

End Interface

Public Class UnitOfWork
    Implements IUnitOfWork

    Public Property Context As Domain.GTGContext Implements IUnitOfWork.Context

    Public Sub New()
        _Context = New GTGContext

    End Sub

    Public Sub Commit() Implements IUnitOfWork.Commit
        _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

Service

Public Class CustomerService
    Private _UOW As IUnitOfWork
    Public Sub New(UOW As IUnitOfWork)
        _UOW = UOW
    End Sub
End Class

Repository

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
End Namespace

Imports System.Data.Objects

Namespace Repositories
    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.Commit()

        End Sub

#End Region

    End Class
End Namespace

Answer 1

That’s OK, just make sure you to pick proper naming for it like UnitOfWorkEF. You should also remove the EF context from the IUnitOfWork interface as it would be tightly coupled to the data access technology. You could instead have the context only inside the specific UnitOfWorkEF class.