获取对象的DataContext

如果我有LINQ对象:

public class SampleDataContext : DataContext {
    public Table Customers { get { return this.GetTable(); } }
    public SampleDataContext( string connectionString ) : base( connectionString ) { }
}

[Table( Name="dbo.tblCustomers" )]
public class Customer {
    private Guid? customerID;
    [Column( Storage="customerID", DbType="uniqueidentifier NOT NULL", IsPrimaryKey=true )]
    public Guid? CustomerID {
        get { return this.customerID; }
        set { this.customerID = value; }
    }

    private string customerName;
    [Column( Storage = "customerName", DbType = "nvarchar(255) NOT NULL" )]
    public string CustomerName {
        get { return this.customerName; }
        set { this.customerName = value; }
    }
}

以及申请中的其他地方:

public static void DoSomethingWithCustomer( Customer customer ) {
    // some operations
    // now, I want save changes to the database
}

如何获取追踪"客户"对象变化的DataContext实例？

编辑:为什么我不想将DataContext传递给方法.

1)总是传递2个对象而不是1个是整个应用程序的"丑陋"模式.

方法将需要每个业务对象的下一个参数.

收集将需要从"列表"更改为"列表>".

这两点都难以维护 - 开发人员必须每次都设置正确的DataContext实例(易于创建错误),尽管DataContext知道具体对象是否(或没有)附加到另一个DataContext.

2)我想(当前版本的应用程序使用它)处理来自不同"地方"的对象集合的"任何"业务逻辑(例如通过拖放浮动窗口).

Currentyl我们使用自定义类型的DataSet,因此有关更改的信息在数据行(DataRow =业务对象)中,并且获取它没有问题,或者创建克隆然后将其保存到数据库中.

凯文-我觉得你的痛苦......当你都在围绕你的业务对象的业务逻辑,有些时候你只是必须能够访问到DataContext到一个对象所属的,因为不知道不必把你的代码在DataContext menas在减少代码可维护性的地方.

我写了下面的代码(VB,我很害怕),它提供了一个Context属性,可以放在数据对象上,然后用于返回该对象所附加的DataContext(如果有的话).

Private Const StandardChangeTrackerName As String = "System.Data.Linq.ChangeTracker+StandardChangeTracker"

Private _context As DataClasses1DataContext
Public Property Context() As DataClasses1DataContext
    Get
        Dim hasContext As Boolean = False
        Dim myType As Type = Me.GetType()
        Dim propertyChangingField As FieldInfo = myType.GetField("PropertyChangingEvent", BindingFlags.NonPublic Or BindingFlags.Instance)
        Dim propertyChangingDelegate As PropertyChangingEventHandler = propertyChangingField.GetValue(Me)
        Dim delegateType As Type = Nothing

        For Each thisDelegate In propertyChangingDelegate.GetInvocationList()
            delegateType = thisDelegate.Target.GetType()
            If delegateType.FullName.Equals(StandardChangeTrackerName) Then
                propertyChangingDelegate = thisDelegate
                hasContext = True
                Exit For
            End If
        Next

        If hasContext Then
            Dim targetField = propertyChangingDelegate.Target
            Dim servicesField As FieldInfo = targetField.GetType().GetField("services", BindingFlags.NonPublic Or BindingFlags.Instance)
            If servicesField IsNot Nothing Then

                Dim servicesObject = servicesField.GetValue(targetField)

                Dim contextField As FieldInfo = servicesObject.GetType.GetField("context", BindingFlags.NonPublic Or BindingFlags.Instance)

                _context = contextField.GetValue(servicesObject)

            End If
        End If

        Return _context
    End Get
    Set(ByVal value As DataClasses1DataContext)

        _context = value

    End Set

End Property

这是一个C#版本:

public DataContext GetMyDataContext()
{
    // Find the StandardChangeTracker listening to property changes on this object.
    // If no StandardChangeTracker is listening, then this object is probably not
    // attached to a data context.
    var eventField = this.GetType().GetField("PropertyChangingEvent", BindingFlags.NonPublic | BindingFlags.Instance);
    var eventDelegate = eventField.GetValue(this) as Delegate;
    if (eventDelegate == null)
        return null;
    eventDelegate = eventDelegate.GetInvocationList().FirstOrDefault(
        del => del.Target.GetType().FullName == "System.Data.Linq.ChangeTracker+StandardChangeTracker");
    if (eventDelegate == null)
        return null;

    // Dig through the objects to get the underlying DataContext.
    // If the following fails, then there was most likely an internal change
    // to the LINQ-to-SQL framework classes.
    var targetField = eventDelegate.Target;
    var servicesField = targetField.GetType().GetField("services", BindingFlags.NonPublic | BindingFlags.Instance);
    var servicesObject = servicesField.GetValue(targetField);
    var contextField = servicesObject.GetType().GetField("context", BindingFlags.NonPublic | BindingFlags.Instance);
    return (DataContext)contextField.GetValue(servicesObject);
}

请注意,如果对象当前已连接到已启用ChangeTracking的上下文,则它只能找到它的DataContext.此属性依赖于DataContext已订阅对象的OnPropertyChanging事件以监视对象生命周期内的更改这一事实.

如果这有用,请向上投票.

有关使用反射查找事件处理程序的更多信息,请 访问:http: //weblogs.asp.net/avnerk/archive/2007/03/29/reflecting-over-an-event.aspx http://www.bobpowell.net/ eventsubscribers.htm