检测单个实体是否需要保存在EF4和WPF中

我正在努力检测EF4中的实体是否有需要保存的更改

离开.NET几年后，我肯定会用rusty这个词来形容我现在的处境。我正在努力学习使用EF4和WPF，同时用.NET重新认识自己。我已经学习了很多关于实体框架和WPF的拖放数据绑定的教程，并用几个窗口构建了一个应用程序，让我的知识一点一点地积累起来

我正在使用我的模型中最简单的部分进行训练练习，该模型有实体：网络和实验室，网络和实验室之间存在多对多的联系，即网络实验室，这种关系现在并不特别重要，因为我仍然处于最基本的阶段

我有一个窗口，在列表框中显示网络列表，旁边有一个数据网格，显示网络中的实验室。根据教程，我可以很容易地做到这一点，最后我得到了如下代码：

Public Class NetworkListWindow

Private Function GetNetworksQuery(entities As UKNEQASEntities) As ObjectQuery(Of Network)

    Dim networksQuery As ObjectQuery(Of Network) = entities.Networks
    ' Update the query to include NetworkLabs data in Networks.
    networksQuery = networksQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networksQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    Dim entities As UKNEQASEntities = New UKNEQASEntities()
    ' Load data into Networks.
    Dim networksViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworksQuery(entities)
    networksViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

End Sub

End Class

Public Class NetworkWindow

Private m_id As Integer
Private m_db As New UKNEQASEntities

Public Sub New(id As Integer)

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    m_id = id

End Sub

Private Function GetNetworkQuery() As ObjectQuery(Of Network)

    Dim networkQuery As ObjectQuery(Of Network) = m_db.Networks
    ' Update the query to include only the Network we are editing
    networkQuery = networkQuery.Where(Function(net) net.Id = m_id)
    ' Update the query to include NetworkLabs data in Networks.
    networkQuery = networkQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networkQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    ' Load data into Networks.
    Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworkQuery()
    networkViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

    ' Get laboratories that are not in any networks
    Dim labResult = From laboratory In m_db.Laboratories _
                    Where _
                    Not _
                    (From networklab In m_db.NetworkLabs _
                     Select networklab.Laboratory.Id).Contains(laboratory.Id) _
                    Select laboratory

    Dim laboratoriesViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesLaboratoriesViewSource"), CollectionViewSource)
    laboratoriesViewSource.Source = labResult.ToList

End Sub

End Class

     Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
     Dim entry As ObjectStateEntry = m_db.ObjectStateManager.GetObjectStateEntry(....)

该窗口仅用于查看，用户可以单击编辑按钮编辑所选网络。第二个窗口是我遇到问题的地方，在该窗口中，我从“数据源”窗口拖动网络实体，创建一个详细信息屏幕，在行和列中创建一个带有标签和文本框的网格。我最终得到了如下代码：

Public Class NetworkListWindow

Private Function GetNetworksQuery(entities As UKNEQASEntities) As ObjectQuery(Of Network)

    Dim networksQuery As ObjectQuery(Of Network) = entities.Networks
    ' Update the query to include NetworkLabs data in Networks.
    networksQuery = networksQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networksQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    Dim entities As UKNEQASEntities = New UKNEQASEntities()
    ' Load data into Networks.
    Dim networksViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworksQuery(entities)
    networksViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

End Sub

End Class

Public Class NetworkWindow

Private m_id As Integer
Private m_db As New UKNEQASEntities

Public Sub New(id As Integer)

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    m_id = id

End Sub

Private Function GetNetworkQuery() As ObjectQuery(Of Network)

    Dim networkQuery As ObjectQuery(Of Network) = m_db.Networks
    ' Update the query to include only the Network we are editing
    networkQuery = networkQuery.Where(Function(net) net.Id = m_id)
    ' Update the query to include NetworkLabs data in Networks.
    networkQuery = networkQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networkQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    ' Load data into Networks.
    Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworkQuery()
    networkViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

    ' Get laboratories that are not in any networks
    Dim labResult = From laboratory In m_db.Laboratories _
                    Where _
                    Not _
                    (From networklab In m_db.NetworkLabs _
                     Select networklab.Laboratory.Id).Contains(laboratory.Id) _
                    Select laboratory

    Dim laboratoriesViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesLaboratoriesViewSource"), CollectionViewSource)
    laboratoriesViewSource.Source = labResult.ToList

End Sub

End Class

     Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
     Dim entry As ObjectStateEntry = m_db.ObjectStateManager.GetObjectStateEntry(....)

这对于显示在上一个屏幕上选择的网络很好，我在工具栏上放了一个保存按钮，它只需调用

m_db.SaveChanges()

保存更改，这样也可以正常工作。我的问题是，当用户编辑数据并关闭窗口时，我想检测当前网络是否需要保存回数据库，以便我可以提示用户，但我不知道如何获取网络以进行检查

我怀疑这与以下代码有关：

Public Class NetworkListWindow

Private Function GetNetworksQuery(entities As UKNEQASEntities) As ObjectQuery(Of Network)

    Dim networksQuery As ObjectQuery(Of Network) = entities.Networks
    ' Update the query to include NetworkLabs data in Networks.
    networksQuery = networksQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networksQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    Dim entities As UKNEQASEntities = New UKNEQASEntities()
    ' Load data into Networks.
    Dim networksViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworksQuery(entities)
    networksViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

End Sub

End Class

Public Class NetworkWindow

Private m_id As Integer
Private m_db As New UKNEQASEntities

Public Sub New(id As Integer)

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    m_id = id

End Sub

Private Function GetNetworkQuery() As ObjectQuery(Of Network)

    Dim networkQuery As ObjectQuery(Of Network) = m_db.Networks
    ' Update the query to include only the Network we are editing
    networkQuery = networkQuery.Where(Function(net) net.Id = m_id)
    ' Update the query to include NetworkLabs data in Networks.
    networkQuery = networkQuery.Include("NetworkLabs")
    ' Returns an ObjectQuery
    Return networkQuery

End Function

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

    ' Load data into Networks.
    Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
    Dim networksQuery As ObjectQuery(Of Network) = GetNetworkQuery()
    networkViewSource.Source = networksQuery.Execute(MergeOption.AppendOnly)

    ' Get laboratories that are not in any networks
    Dim labResult = From laboratory In m_db.Laboratories _
                    Where _
                    Not _
                    (From networklab In m_db.NetworkLabs _
                     Select networklab.Laboratory.Id).Contains(laboratory.Id) _
                    Select laboratory

    Dim laboratoriesViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesLaboratoriesViewSource"), CollectionViewSource)
    laboratoriesViewSource.Source = labResult.ToList

End Sub

End Class

     Dim networkViewSource As CollectionViewSource = CType(Me.FindResource("UKNEQASEntitiesNetworksViewSource"), CollectionViewSource)
     Dim entry As ObjectStateEntry = m_db.ObjectStateManager.GetObjectStateEntry(....)

但我不知道如何让网络传递到GetObjectStateEntry

在我以前的列表屏幕上，我可以通过从列表框中获取SelectedItem来获取所选网络，但在我的单个输入窗口中找不到任何有助于我的东西

我这样做对吗？对于单条目编辑屏幕，我仍然像列表屏幕一样使用CollectionViewSource，这是最好的方法还是对单个实体有什么好处

我一直在寻找很多教程，我发现大部分都是关于在DataGrids中显示数据以进行编辑的，这不是我要找的。我很难找到任何帮助来制作编辑单个实体的屏幕，因此不知道如何获取用户正在编辑的实体的引用

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非常感谢您的帮助，因为我是EF和XAML lark的新手。

您从错误的角度看待它。当你开始使用EF时需要考虑的几个问题：

你几乎不需要看 ObjectStateManager，这是一个 EF应该为你做些什么。例如，如果你 要关闭窗口并保存吗 一切，打电话就行了 context.SaveChanges并让EF 找出需要什么的工作 存钱什么的。在某些情况下，您需要使用ObjectStateManager，但这些都是特定的，并且通常与非常定制的内容相关联

你看到的例子不多， 因为建造WPF的人 而Silverlight应用程序并非如此 连接到数据库引擎， 相反，它们连接到一个或多个 Web服务层和交互层 和他们在一起。当你这样做的时候 发生的第一件事是你没有 长时间使用正常EF 实体，这些并不是被制造出来的 连载。你将与任何一方合作 自跟踪的POCO实体 实体

如果使用的是法线实体， 它们被设计用于所有方面 附加到您案例中的上下文 它将是：英国公民，这个 意味着如果您尝试使用此 在客户端应用程序中，您将需要 确保您始终使用相同的 上下文，所以两者都有一个引用 在Singleton类或inject上执行此操作 它是在依赖注入中实现的 容器如果使用多个 你会遇到很多人 与该计划有关的问题 指定给对象的EntityKey 就其存在的背景而言 在上下文中考虑记忆 数据库的副本，这不是 事实上，它的工作原理更像 您用来 自动生成针对的sql查询 你的数据库

最后，如果要构建良好的WPF客户端应用程序，还需要使用：

依赖项注入容器： 部署在 Net部署或 哪个是企业的一部分 图书馆 EF4 I 我个人喜欢这些而不是POCO 对象，因为你会得到很多 免费提供强大的功能。 如果你需要更具体的帮助，你也可以直接打电话给我，我已经在中大型项目的专业开发团队中工作了一段时间。然而，我从来没有工作过

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VisualBasic，所以当我不得不阅读VB代码时，我有点痛苦

感谢您的回复，我想我正在进入一个痛苦的世界，在WPF示例中遵循MS的EF4。示例显示了将两个实体绑定到主窗口上的ListBox/datagrids，然后显示创建一个save按钮来调用上下文中的.SaveChanges，然后停止。我正在尝试构建一个应用程序，其中有少量实体，它们之间有很多关系，用户需要能够进行更改、保存更改、恢复更改，取消这些内容，因此在扩展我对MS示例的理解时，我很难应用所有这些内容。我按照您的建议将我的上下文放在一个Singleton类上，我的编辑窗口现在可以检测是否有需要保存的更改，这样我就可以给用户一个标准提示：是否要保存更改？Yes调用。SaveChanges、cancel停止关闭窗口，而No在恢复更改时不执行任何操作。当一个单例类的上下文不做任何事情时，意味着编辑后的网络仍然拥有我返回上一个窗口时所做的所有更改。有没有一种简单的方法可以还原上下文中的更改？