.net 获取对象';数据上下文
如果我有LINQ对象:.net 获取对象';数据上下文,.net,linq-to-sql,c#-3.0,datacontext,.net,Linq To Sql,C# 3.0,Datacontext,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
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; }
}
}
如何获取跟踪“customer”对象更改的DataContext实例
编辑:为什么我不想将DataContext传递到方法中。
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
- 方法将需要每个业务对象的下一个参数
- 集合将需要从“列表”更改为“列表>”
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=业务对象)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。最简单的方法是将DataContext传递到方法中
但是,你也可以考虑改变你的设计,让你遵循“一个方法只有一个目的”的规则,在这种情况下,你不想用“修改”的方法来“保存”。
< P>部分乐趣在于你不能确定对象知道谁在跟踪他。如果对象具有数据感知/延迟加载属性,那么您可能能够通过反射跟踪上下文,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会更干净。Kevin-我感觉到了你的痛苦。。。当您围绕业务对象构建业务逻辑时,有时您只需要访问对象所属的DataContext,因为不知道DataContext菜单就必须将代码放在降低代码可维护性的地方 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
这是一个C版本:
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:
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);
}