HOW TO：自訂產生的資料物件 (Entity Framework)
本主題說明如何將自訂方法加入到產生的資料類別。本主題的範例是根據 Adventure Works Sales Model。若要執行此範例中的程式碼，您必須已經將 AdventureWorks Sales Model 加入到專案中，並設定您的專案使用 Entity Framework。若要這樣做，請完成 HOW TO：手動設定 Entity Framework 專案和 HOW TO：手動定義模型和對應檔 (Entity Framework) 中的程序。
範例
此範例會針對產生的 SalesOrderHeader 類別定義自訂 UpdateOrderTotal 方法。此自訂方法會根據目前的稅、運費和個別項目總和的值來更新 TotalDue 屬性。這個方法會定義為部分類別，因此當 Entity Framework 工具重新產生 SalesOrderHeader 類別時，它就不會遺失。
Partial Public Class SalesOrderHeader
' Update the order total.
Public Sub UpdateOrderTotal()
Dim newSubTotal As Decimal = 0
' Ideally, this information is available in the EDM.
Dim taxRatePercent As Decimal = GetCurrentTaxRate()
Dim freightPercent As Decimal = GetCurrentFreight()
' If the items for this order are loaded or if the order is
' newly added, then recalculate the subtotal as it may have changed.
If Me.SalesOrderDetails.IsLoaded OrElse EntityState = EntityState.Added Then
For Each item As SalesOrderDetail In Me.SalesOrderDetails
' Calculate line totals for loaded items.
newSubTotal += (item.OrderQty * (item.UnitPrice - item.UnitPriceDiscount))
Next
Me.SubTotal = newSubTotal
End If
' Calculate the new tax amount.
Me.TaxAmt = Me.SubTotal + Decimal.Round((Me.SubTotal * taxRatePercent / 100), 4)
' Calculate the new freight amount.
Me.Freight = Me.SubTotal + Decimal.Round((Me.SubTotal * freightPercent / 100), 4)
' Calculate the new total.
Me.TotalDue = Me.SubTotal + Me.TaxAmt + Me.Freight
End Sub
End Class
public partial class SalesOrderHeader
{
// Update the order total.
public void UpdateOrderTotal()
{
decimal newSubTotal = 0;
// Ideally, this information is available in the EDM.
decimal taxRatePercent = GetCurrentTaxRate();
decimal freightPercent = GetCurrentFreight();
// If the items for this order are loaded or if the order is
// newly added, then recalculate the subtotal as it may have changed.
if (this.SalesOrderDetails.IsLoaded ||
EntityState == EntityState.Added)
{
foreach (SalesOrderDetail item in this.SalesOrderDetails)
{
// Calculate line totals for loaded items.
newSubTotal += (item.OrderQty *
(item.UnitPrice - item.UnitPriceDiscount));
}
this.SubTotal = newSubTotal;
}
// Calculate the new tax amount.
this.TaxAmt = this.SubTotal
+ Decimal.Round((this.SubTotal * taxRatePercent / 100), 4);
// Calculate the new freight amount.
this.Freight = this.SubTotal
+ Decimal.Round((this.SubTotal * freightPercent / 100), 4);
// Calculate the new total.
this.TotalDue = this.SubTotal + this.TaxAmt + this.Freight;
}
}
此範例會修改訂單，然後在 SalesOrderHeader 上呼叫自訂 UpdateOrderTotal 方法來更新 TotalDue 屬性。因為 TotalDue 具有套用於存放結構定義語言 (SSDL) 檔案的 StoreGeneratedPattern="computed" 屬性，所以呼叫 SaveChanges 時，並不會將這個更新值儲存至伺服器。如果沒有這個屬性，當您嘗試在伺服器上更新計算資料行時，將會發生 UpdateException。
Dim orderId As Integer = 43662
Using context As New AdventureWorksEntities()
' Return an order and its items.
Dim order As SalesOrderHeader = context.SalesOrderHeaders.Include("SalesOrderDetails") _
.Where("it.SalesOrderID = @orderId", _
New ObjectParameter("orderId", orderId)).First()
Console.WriteLine("The original order total was: " & order.TotalDue)
' Update the order status.
order.Status = 1
' Increase the quantity of the first item, if one exists.
If order.SalesOrderDetails.Count > 0 Then
order.SalesOrderDetails.First().OrderQty += 1
End If
' Increase the shipping amount by 10%.
order.Freight = Decimal.Round(order.Freight * CDec(1.1), 4)
' Call the custom method to update the total.
order.UpdateOrderTotal()
Console.WriteLine("The calculated order total is: " & order.TotalDue)
' Save changes in the object context to the database.
Dim changes As Integer = context.SaveChanges()
' Refresh the order to get the computed total from the store.
context.Refresh(RefreshMode.StoreWins, order)
Console.WriteLine("The store generated order total is: " & order.TotalDue)
End Using
int orderId = 43662;
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Return an order and its items.
SalesOrderHeader order =
context.SalesOrderHeaders
.Include("SalesOrderDetails")
.Where("it.SalesOrderID = @orderId",
new ObjectParameter("orderId", orderId)).First();
Console.WriteLine("The original order total was: "
+ order.TotalDue);
// Update the order status.
order.Status = 1;
// Increase the quantity of the first item, if one exists.
if (order.SalesOrderDetails.Count > 0)
{
order.SalesOrderDetails.First().OrderQty += 1;
}
// Increase the shipping amount by 10%.
order.Freight =
Decimal.Round(order.Freight * (decimal)1.1, 4);
// Call the custom method to update the total.
order.UpdateOrderTotal();
Console.WriteLine("The calculated order total is: "
+ order.TotalDue);
// Save changes in the object context to the database.
int changes = context.SaveChanges();
// Refresh the order to get the computed total from the store.
context.Refresh(RefreshMode.StoreWins, order);
Console.WriteLine("The store generated order total is: "
+ order.TotalDue);
}