使用部分方法加入商務邏輯 (LINQ to SQL)
更新： November 2007
您可以使用「部分方法」(Partial Method)，在 LINQ to SQL 專案中自訂 Visual Basic 和 C# 產生的程式碼。LINQ to SQL 產生的程式碼會將簽章定義成部分方法的一部分。如果您想實作此方法，可以加入自己的部分方法。如果您未加入自己的實作 (Implementation)，則編譯器 (Compiler) 會捨棄部分方法簽章並呼叫 LINQ to SQL 中的預設方法。
.gif "注意事項") 注意事項： |
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如果您使用的是 Visual Studio，可以使用物件關聯式設計工具將驗證和其他自訂加入至實體 (Entity) 類別 (Class)。 |
例如，Northwind 範例資料庫中 Customer 類別的預設對應包含下列部分方法：
Partial Private Sub OnAddressChanged()
End Sub
partial void OnAddressChanged();
您可以將下列程式碼加入至自己的部分 Customer 類別，進而實作自己的方法：
Partial Class Customer
Private Sub OnAddressChanged()
' Insert business logic here.
End Sub
End Class
public partial class Customer
{
partial void OnAddressChanged();
partial void OnAddressChanged()
{
// Insert business logic here.
}
}
這種方法通常用於 LINQ to SQL 中，以覆寫 Insert、Update、Delete 的預設方法，以及驗證物件生命週期事件中的屬性。
如需詳細資訊，請參閱部分方法 (Visual Basic) 或 partial (方法) (C#)。
範例
說明
下列範例會先顯示 ExampleClass，因為它可能是由程式碼產生工具 (例如 SQLMetal) 所定義，然後顯示您如何僅實作其中一種方法。
程式碼
' Code-generating tool defines a partial class, including
' two partial methods.
Partial Class ExampleClass
Partial Private Sub OnFindingMaxOutput()
End Sub
Partial Private Sub OnFindingMinOutput()
End Sub
Sub ExportResults()
OnFindingMaxOutput()
OnFindingMinOutput()
End Sub
End Class
' Developer implements one of the partial methods. Compiler
' discards the other method.
Class ExampleClass
Private Sub OnFindingMaxOutput()
Console.WriteLine("Maximum has been found.")
End Sub
End Class
// Code-generating tool defines a partial class, including
// two partial methods.
partial class ExampleClass
{
partial void onFindingMaxOutput();
partial void onFindingMinOutput();
}
// Developer implements one of the partial methods. Compiler
// discards the signature of the other method.
partial class ExampleClass
{
partial void onFindingMaxOutput()
{
Console.WriteLine("Maximum has been found.");
}
}
範例
說明
下列範例會使用 Shipper 和 Order 實體 (Entity) 之間的關聯性 (Relationship)。請注意部分方法中的 InsertShipper 和 DeleteShipper 方法。這些方法會覆寫 LINQ to SQL 對應所提供的預設部分方法。
程式碼
Public Shared LoadOrdersCalled As Integer = 0
Private Function LoadOrders(ByVal shipper As Shipper) As _
IEnumerable(Of Order)
LoadOrdersCalled += 1
Return Me.Orders.Where(Function(o) o.ShipVia = _
shipper.ShipperID)
End Function
Public Shared LoadShipperCalled As Integer = 0
Private Function LoadShipper(ByVal order As Order) As Shipper
LoadShipperCalled += 1
Return Me.Shippers.Single(Function(s) s.ShipperID = _
order.ShipVia)
End Function
Public Shared InsertShipperCalled As Integer = 0
Private Sub InsertShipper(ByVal instance As Shipper)
InsertShipperCalled += 1
' Call a Web service to perform an insert operation.
InsertShipperService(shpr:=Nothing)
End Sub
Public Shared UpdateShipperCalled As Integer = 0
Private Sub UpdateShipper(ByVal original As Shipper, ByVal current _
As Shipper)
UpdateShipperCalled += 1
' Call a Web service to update shipper.
InsertShipperService(shpr:=Nothing)
End Sub
Public Shared DeleteShipperCalled As Boolean
Private Sub DeleteShipper(ByVal instance As Shipper)
DeleteShipperCalled = True
End Sub
public static int LoadOrdersCalled = 0;
private IEnumerable<Order> LoadOrders(Shipper shipper)
{
LoadOrdersCalled++;
return this.Orders.Where(o => o.ShipVia == shipper.ShipperID);
}
public static int LoadShipperCalled = 0;
private Shipper LoadShipper(Order order)
{
LoadShipperCalled++;
return this.Shippers.Single(s => s.ShipperID == order.ShipVia);
}
public static int InsertShipperCalled = 0;
partial void InsertShipper(Shipper shipper)
{
InsertShipperCalled++;
// Call a Web service to perform an insert operation.
InsertShipperService(shipper);
}
public static int UpdateShipperCalled = 0;
private void UpdateShipper(Shipper original, Shipper current)
{
Shipper shipper = new Shipper();
UpdateShipperCalled++;
// Call a Web service to update shipper.
InsertShipperService(shipper);
}
public static bool DeleteShipperCalled;
partial void DeleteShipper(Shipper shipper)
{
DeleteShipperCalled = true;
}