实体框架：如何在断开连接的方案中更新具有独立关联的实体？

Question

我正在尝试使用已在UI中更改的独立关联更新对象。加载和保存在不同的DBContexts中进行。我尝试了以下，但现在我被卡住了。我偶尔会遇到DBUpdateExceptions。

EFTestConsole.UserList.Update: System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception. Handling of exceptions while saving can be made easier by exposing foreign key properties in your entity types. See the InnerException for details. ---> System.Data.Entity.Core.OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.

据我所知，这源于现有对象之间的现有关系，这些关系由Entity Framework添加并且未包含在导航属性中，并且在绘制状态时我没有设置为Unchanged。但是如何识别它们呢？

这就是我到目前为止所做的：

1. 将修改后的对象添加到DBContext并将其状态设置为Modified。
2. 通过将状态设置为已删除，删除与导航属性中删除的对象（存在于数据库中）的关系。
3. 为当前包含在导航属性中的所有对象绘制状态：将现有对象的状态（ID> 0）和关系设置为Unchanged，并将新对象的状态（ID = 0）及其关系设置为Added
4. 绘制对象的状态，这些对象已添加到naviagtion属性中：将对象的状态设置为Unchanged（如果已存在：ID＆gt; 0）oder Added（如果new：ID = 0），以及状态与添加的关系。
5. 从DBContext中删除所有对象和关系，这些对象和关系由实体框架添加到上下文中，但不包含在（旧的或当前的）导航属性中。

以下是代码：

Public Function Update(ByVal userToProcess As User) As Boolean
    Dim Success As Boolean = False
            ' Compute, which objects in the navigation properties were added resp. removed.

            ' Register userToProcess in TempDBContext.
            TempDBContext.UserDBSet.Add(userToProcess)
            TempDBContext.Entry(userToProcess).State = EntityState.Modified

            ' Fixing relationships to objects in navigation properties in 3 steps:
            ' 1. Deleting relationships to objects, which remain in database.
            For Each adg As ADGroup In UsersADGroupsToDelete
                If TempDBContext.Entry(adg).State = EntityState.Detached Then
                    adg = TempDBContext.ADGroupDBSet.Find(adg.ID)
                    TempDBContext.Entry(adg).State = EntityState.Unchanged
                End If
                TempDBContext.Core.ObjectStateManager _
                    .ChangeRelationshipState( _
                        userToProcess, _
                        adg, _
                        "UsersADGroupsList", _
                        EntityState.Deleted)
            Next

            For Each ug As Group In UsersGroupsToDelete
                If TempDBContext.Entry(ug).State = EntityState.Detached Then
                    ug = TempDBContext.GroupDBSet.Find(ug.ID)
                    TempDBContext.Entry(ug).State = EntityState.Unchanged
                End If
                TempDBContext.Core.ObjectStateManager _
                    .ChangeRelationshipState( _
                        userToProcess, _
                        ug, _
                        "UsersGroupsList", _
                        EntityState.Deleted)
            Next

            ' 2.1. Setting objects and relationships to Unchanged for all existing objects in navigation properties.
            ' 2.2. Settings objects and relationships to Added for all new objects (ID = 0) in naviagtion properties.
            For Each adg As ADGroup In userToProcess.UsersADGroupsList
                If adg.ID > 0 Then
                    TempDBContext.Entry(adg).State = EntityState.Unchanged
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            adg, _
                            "UsersADGroupsList", _
                            EntityState.Unchanged)
                Else
                    TempDBContext.Entry(adg).State = EntityState.Added
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            adg, _
                            "UsersADGroupsList", _
                            EntityState.Added)
                End If
            Next

            For Each ug As Group In userToProcess.UsersGroupsList
                If ug.ID > 0 Then
                    TempDBContext.Entry(ug).State = EntityState.Unchanged
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            ug, _
                            "UsersGroupsList", _
                            EntityState.Unchanged)
                Else
                    TempDBContext.Entry(ug).State = EntityState.Added
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            ug, _
                            "UsersGroupsList", _
                            EntityState.Added)
                End If
            Next

            ' 3. Setting objects to Unchanged, which exist in the database, but are newly related to userToProcess.

            For Each adg As ADGroup In UsersADGroupsToAdd
                If adg.ID > 0 Then
                    TempDBContext.Entry(adg).State = EntityState.Unchanged
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            adg, _
                            "UsersADGroupsList", _
                            EntityState.Added)
                Else
                    TempDBContext.Entry(adg).State = EntityState.Added
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            adg, _
                            "UsersADGroupsList", _
                            EntityState.Added)
                End If

            Next

            For Each ug As Group In UsersUserGroupsToAdd
                If ug.ID > 0 Then
                    TempDBContext.Entry(ug).State = EntityState.Unchanged
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            ug, _
                            "UsersGroupsList", _
                            EntityState.Added)
                Else
                    TempDBContext.Entry(ug).State = EntityState.Added
                    TempDBContext.Core.ObjectStateManager _
                        .ChangeRelationshipState( _
                            userToProcess, _
                            ug, _
                            "UsersGroupsList", _
                            EntityState.Added)
                End If
            Next

            ' EntityFramework adds more objects and relationships to DBContext than are contained within the navigation properties.
            ' These are to be deleted now.
            Dim TempGroupForType As Group = New Group
            Dim TempGroupType As System.Type = TempGroupForType.GetType()
            Dim TempADGroupForType As ADGroup = New ADGroup
            Dim TempADGroupType As System.Type = TempADGroupForType.GetType()
            Dim TempUserForType As User = New User
            Dim TempUserType As System.Type = TempUserForType.GetType()

            For Each e As System.Data.Entity.Infrastructure.DbEntityEntry(Of Modelbase) _
                In TempDBContext.ChangeTracker.Entries(Of Modelbase)()
                Select Case e.Entity.GetType()
                    Case TempGroupType
                        Dim TempGroup As Group = TryCast(e.Entity, Group)
                        If TempGroup IsNot Nothing _
                            AndAlso TempGroup.ID > 0 _
                            AndAlso TempGroup.ParentGroup IsNot Nothing _
                            AndAlso TempGroup.ParentGroup.ID > 0 Then
                            ' Detach relations to parent groups from DBContext.
                            TempDBContext.Core.ObjectStateManager _
                                                            .ChangeRelationshipState( _
                                                                TempGroup, _
                                                                TempGroup.ParentGroup, _
                                                                "ParentGroup", _
                                                                EntityState.Detached)
                        End If
                        If e.State = EntityState.Added _
                                AndAlso TempGroup IsNot Nothing _
                                AndAlso TempGroup.ID > 0 Then
                            e.State = EntityState.Detached
                        End If
                    Case TempADGroupType
                        Dim TempADGroup As ADGroup = TryCast(e.Entity, ADGroup)
                        If e.State = EntityState.Added _
                            AndAlso TempADGroup IsNot Nothing _
                            AndAlso TempADGroup.ID > 0 Then
                            e.State = EntityState.Detached
                        End If
                    Case TempUserType
                        Dim TempUser As User = TryCast(e.Entity, User)
                        If e.State = EntityState.Added _
                            AndAlso TempUser IsNot Nothing _
                            AndAlso TempUser.ID > 0 Then
                            e.State = EntityState.Detached
                        End If
                End Select
            Next

            ' Save changes to database.
            TempDBContext.SaveChanges()

            Success = True

        End Using

    Return Success
End Function

对象看起来像这样。有用户，可以属于多个组（n：m）。可选地，它们可以属于AD组（n：m），并且组和AD组之间可以存在（1：1）关系。

Public Class User
    Inherits ModelBase

    Public Property ID() As Integer
    Public Property UserName() As String
    ' List of AD groups to which the user belongs.
    Public Property UsersADGroupsList() As List(Of ADGroup)
    ' List of groups to which the user belongs.
    Public Property UsersGroupsList() As List(Of Group)

    Public Sub New()
        _UsersADGroupsList = New List(Of ADGroup)
        _UsersGroupsList = New List(Of Group)
    End Sub

End Class

Public Class ADGroup
    Inherits ModelBase

    Public Property ID() As Integer
    Public Property Name() As String
    ' List of related users.
    Public Property RelatedUsersList() As List(Of User)
    ' Reference to related group.
    Public Property RelatedGroup() As Group

    Public Sub New()
        _RelatedUsersList = New List(Of User)
    End Sub

End Class

Public Class Group
    Inherits ModelBase

    Public Property ID() As Integer
    Public Property Name() As String
    ' List of related users.
    Public Property UserList() As List(Of User)
    ' Reference to parent group.
    Public Property ParentGroup() As Group
    ' List of children groups.
    Public Property ChildrenGroupsList() As List(Of Group)
    ' Reference to AD group.
    Public Property RelatedADGroup As ADGroup

    Public Sub New()
        _UserList = New List(Of User)
        _ChildrenGroupsList = New List(Of Group)
    End Sub

End Class

最后是DBContext：

Public Class MyDBContext
    Inherits DBContext

    ' DBSets for the classes below.
    Public Property UserDBSet As DbSet(Of User)
    Public Property GroupDBSet As DbSet(Of Group)
    Public Property ADGroupDBSet As DbSet(Of ADGroup)
    ' Access to ObjectContext below DBContext.
    Private _Core As ObjectContext
    Public Property Core() As ObjectContext
        Get
            Return TryCast(Me, IObjectContextAdapter).ObjectContext
        End Get
        Private Set(ByVal value As ObjectContext)
            _Core = value
        End Set
    End Property

    Public Sub New()

    End Sub

    Public Sub New(ByVal nameOrConnectionString As String)
        MyBase.New(nameOrConnectionString)
    End Sub

    ' Controls the generation of the db model.
    Protected Overrides Sub OnModelCreating(modelBuilder As DbModelBuilder)
        modelBuilder.Configurations.Add(New ADGroupConfiguration())
        modelBuilder.Configurations.Add(New GroupConfiguration())
        modelBuilder.Configurations.Add(New UserConfiguration())
    End Sub

End Class

Public Class UserConfiguration
    Inherits EntityTypeConfiguration(Of User)

    Public Sub New()
        ' Defining optional and required properties.
        [Property](Function(u) u.UserName).IsRequired()

        ' Defining n:m-relationships.
        HasMany(Function(u) u.UsersGroupsList).WithMany(Function(g) g.UserList)
    End Sub

End Class

Public Class ADGroupConfiguration
    Inherits EntityTypeConfiguration(Of ADGroup)

    Public Sub New()
        ' n:m-relationships.
        HasMany(Function(a) a.RelatedUsersList).WithMany(Function(u) u.UsersADGroupsList)
    End Sub

End Class

Public Class GroupConfiguration
    Inherits EntityTypeConfiguration(Of Group)

    Public Sub New()
        ' Defining 1:1-relationships.
        HasOptional(Function(g) g.RelatedADGroup).WithOptionalDependent(Function(a) a.RelatedGroup)

        ' Defining n:m-relationships.
        HasMany(Function(g) g.UserList).WithMany(Function(u) u.UsersGroupsList).Map(Sub(t)
                                                                                        t.ToTable("UsersGroups")
                                                                                    End Sub)
    End Sub

End Class

我正在使用Entity Framework 6.0.1和Visual Studio 2013。

对我来说，出现了以下问题：

1. 更新对象（图表）时我做错了什么？
2. 我的解决方案虽然受到Lerman＆amp; Miller（2012，编程实体框架：DBContext）的启发，但看起来过于复杂。如何使其更简单？
3. 如何处理异常？我假设会出现乐观并发异常，但我不知道如何处理它们，因为异常不返回对象，这会导致异常。由于独立协会。

我是Entity Framework的新手。所以我的问题可能有一个简单的解决方案。

提前多多感谢。