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获取对象的DataContext

datacontext c#-3.0 linq-to-sql .net

9

TcKs · 技术社区 · 18 年前

如果我有LINQ对象:

public class SampleDataContext : DataContext {
    public Table<Customer> Customers { get { return this.GetTable<Customer>(); } }
    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; }
    }
}

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

如何获取跟踪“customer”对象更改的DataContext实例?

1) 始终传递2个对象而不是1个对象对于整个应用程序来说是“丑陋”的模式。

集合将需要从“列表”更改为“列表”。

2) 我希望(当前版本的应用程序使用it)处理来自不同“位置”的对象集合上的“任何”业务逻辑(例如,通过拖放操作的浮动窗口)。

Currentyl我们使用自定义类型的数据集,因此有关更改的信息位于数据行(DataRow=business object)中,获取它或创建克隆然后将其保存到数据库中并不成问题。

3 回复 | 直到 18 年前

1

6

Andrew Morton 5 年前

凯文-我感觉到你的痛苦。。。当您围绕业务对象构建业务逻辑时,有时您只需有

我编写了以下代码(恐怕是VB),它提供了一个可以放置在数据对象上的上下文属性,然后用于返回对象所附加的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

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,如果对象当前连接到打开了ChangeTracking的上下文,则该对象只能定位其DataContext。此属性依赖于DataContext已订阅对象的OnPropertyChange事件以监视对象生命周期内的更改这一事实。

如果这有帮助,请在这篇文章上投票。

有关使用反射查找事件处理程序的详细信息:

2

3

Marc Gravell 18 年前

POCO 知道谁在跟踪他。如果对象具有数据感知/延迟加载属性,则能够通过反射追踪上下文,但实际上这将是一个混乱。简单地将数据上下文传递给需要它的代码将更为简洁。

3

2

Wayne Bloss 18 年前

最简单的方法是将DataContext传递到方法中。

但是,您也可以考虑更改设计,以便遵循“单个方法只具有一个目的”的规则,在这种情况下,您不希望在“修改”相同的方法中“保存”。