HOW TO：加入、修改和刪除物件 (Entity Framework)

本主題提供的範例將示範如何使用物件服務來修改物件內容中的物件，以及將資料儲存至資料庫。 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：以手動方式定義 Entity Data Model (Entity Framework) 中的程序。

範例

在這則範例中，物件查詢會根據指定的 SalesOrderID 傳回單一 SalesOrderHeader 物件。 這筆訂單的狀態會從 5 (已出貨) 變更為 1 (處理中)、在訂單中加入新的項目，而且刪除第一個現有的項目。 我們會呼叫 SaveChanges 方法，將變更寫入資料庫。 然後，訂單的產生狀態會寫入主控台。

' Specify the order to update.
Dim orderId As Integer = 43680

Using context As New AdventureWorksEntities()
    Try
        Dim order As SalesOrderHeader = _
        context.SalesOrderHeader.Where( _
                "it.SalesOrderID = @id", New ObjectParameter( _
                 "id", orderId)).First()

        ' Change the status and ship date of an existing order.
        order.Status = 1
        order.ShipDate = DateAndTime.Today

        ' Load items for the order, if not already loaded.
        If Not order.SalesOrderDetail.IsLoaded Then
            order.SalesOrderDetail.Load()
        End If

        ' Delete the first item in the order.
        context.DeleteObject(order.SalesOrderDetail.First())

        ' Create a new item using the static Create method
        ' and add it to the order.
        order.SalesOrderDetail.Add( _
            SalesOrderDetail.CreateSalesOrderDetail( _
            1, 0, 2, 750, 1, CDec(2171.2942), 0, 0, Guid.NewGuid(), _
            DateAndTime.Today))

        ' Save changes in the object context to the database.
        Dim changes As Integer = context.SaveChanges()

        Console.WriteLine(changes.ToString() + " changes saved!")
        Console.WriteLine("Updated item for order: " _
            + order.SalesOrderID.ToString())

        Dim item As SalesOrderDetail
        For Each item In order.SalesOrderDetail
            Console.WriteLine("Item ID: " _
                + item.SalesOrderDetailID.ToString() + "  Product: " _
                + item.ProductID.ToString() + "  Quantity: " + item.OrderQty.ToString())
        Next
    Catch ex As UpdateException
        Console.WriteLine(ex.ToString())
    End Try
End Using

// Specify the order to update.
int orderId = 43680;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    try
    {
        SalesOrderHeader order =
            context.SalesOrderHeader.Where
            ("it.SalesOrderID = @id", new ObjectParameter(
             "id", orderId)).First();

        // Change the status and ship date of an existing order.
        order.Status = 1;
        order.ShipDate = DateTime.Today;

        // Load items for the order, if not already loaded.
        if (!order.SalesOrderDetail.IsLoaded)
        {
            order.SalesOrderDetail.Load();
        }

        // Delete the first item in the order.
        context.DeleteObject(order.SalesOrderDetail.First());

        // Create a new item using the static Create method 
        // and add it to the order.
        order.SalesOrderDetail.Add(
            SalesOrderDetail.CreateSalesOrderDetail(0,
            0, 2, 750, 1, (decimal)2171.2942, 0, 0,
            Guid.NewGuid(), DateTime.Today));

        // Save changes in the object context to the database.
        int changes = context.SaveChanges();

        Console.WriteLine(changes.ToString() + " changes saved!");
        Console.WriteLine("Updated item for order: "
            + order.SalesOrderID.ToString());

        foreach (SalesOrderDetail item in order.SalesOrderDetail)
        {
            Console.WriteLine("Item ID: "
                + item.SalesOrderDetailID.ToString() + "  Product: "
                + item.ProductID.ToString() + "  Quantity: "
                + item.OrderQty.ToString());
        }
    }
    catch (UpdateException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另請參閱

概念

加入、修改和刪除物件 (Entity Framework)
物件服務概觀 (Entity Framework)