HOW TO：在儲存變更時執行商務邏輯 (Entity Framework)

發行項
02/28/2011

Entity Framework 可讓您將變更儲存到資料庫之前，先執行自訂商務邏輯。在處理 SaveChanges 作業之前，會先引發 SavingChanges 事件。處理這個事件可在將變更儲存到資料庫之前，先實作自訂商務邏輯。從 .NET Framework 4 版開始，SaveChanges 方法就是 virtual。這表示您可以直接覆寫此方法，而不是訂閱 SavingChanges 事件。

本主題的範例會示範如何覆寫 SaveChanges 方法及處理 SavingChanges 事件，以便在這些變更保存到資料庫之前先驗證物件內容中的已變更物件。

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。

第一個範例顯示如何覆寫自訂物件內容類別中的 SaveChanges 方法。第二個範例示範如何使用 OnContextCreated 在 ObjectContext 的執行個體中註冊 SavingChanges 事件的處理常式。第三個範例示範如何在衍生自 ObjectContext 的 Proxy 類別中處理此事件。第四個範例示範使用來自第二個範例的 Proxy 類別對物件進行變更，然後呼叫 SaveChanges 的程式碼。

範例

在此範例中會覆寫 SaveChanges 方法，讓您驗證具有 Added 或 Modified EntityState 的物件。此範例是根據 HOW TO：定義自訂物件內容 (Entity Framework) 中所定義之自訂物件內容。

Public Overloads Overrides Function SaveChanges(ByVal options As SaveOptions) As Integer

    For Each entry As ObjectStateEntry In ObjectStateManager.GetObjectStateEntries(EntityState.Added Or EntityState.Modified)
        ' Validate the objects in the Added and Modified state 
        ' if the validation fails throw an exeption. 
    Next
    Return MyBase.SaveChanges(options)
End Function

public override int SaveChanges(SaveOptions options)
{

    foreach (ObjectStateEntry entry in
        ObjectStateManager.GetObjectStateEntries(
        EntityState.Added | EntityState.Modified))
    {
        // Validate the objects in the Added and Modified state
        // if the validation fails throw an exeption.
    }
    return base.SaveChanges(options);
}

在此範例中，OnContextCreated 方法是定義成 AdventureWorksEntities 的部分方法。 SavingChanges 事件的處理常式則是定義在這個部分方法中。這個事件處理常式會確認呼叫的程式碼並未在 SalesOrderHeader.Comment 屬性中加入任何不當文字，然後才會保存變更。如果字串檢查演算法 (這裡未顯示) 找到任何問題，就會引發例外狀況。

Partial Public Class AdventureWorksEntities
    Private Sub OnContextCreated()
        ' Register the handler for the SavingChanges event. 
        AddHandler Me.SavingChanges, AddressOf context_SavingChanges
    End Sub
    ' SavingChanges event handler. 
    Private Shared Sub context_SavingChanges(ByVal sender As Object, ByVal e As EventArgs)
        ' Validate the state of each entity in the context 
        ' before SaveChanges can succeed. 
        For Each entry As ObjectStateEntry In DirectCast(sender, ObjectContext).ObjectStateManager.GetObjectStateEntries(EntityState.Added Or EntityState.Modified)
            ' Find an object state entry for a SalesOrderHeader object. 
            If Not entry.IsRelationship AndAlso (entry.Entity.GetType() Is GetType(SalesOrderHeader)) Then
                Dim orderToCheck As SalesOrderHeader = TryCast(entry.Entity, SalesOrderHeader)

                ' Call a helper method that performs string checking 
                ' on the Comment property. 
                Dim textNotAllowed As String = Validator.CheckStringForLanguage(orderToCheck.Comment)

                ' If the validation method returns a problem string, raise an error. 
                If textNotAllowed <> String.Empty Then
                    Throw New ArgumentException(String.Format("Changes cannot be " & _
                                                                "saved because the {0} '{1}' object contains a " & _
                                                                "string that is not allowed in the property '{2}'.", _
                                                                entry.State, "SalesOrderHeader", "Comment"))
                End If
            End If
        Next
    End Sub
End Class

public partial class AdventureWorksEntities
{
    partial void OnContextCreated()
    {
        // Register the handler for the SavingChanges event.
        this.SavingChanges
            += new EventHandler(context_SavingChanges);
    }
    // SavingChanges event handler.
    private static void context_SavingChanges(object sender, EventArgs e)
    {
        // Validate the state of each entity in the context
        // before SaveChanges can succeed.
        foreach (ObjectStateEntry entry in
            ((ObjectContext)sender).ObjectStateManager.GetObjectStateEntries(
            EntityState.Added | EntityState.Modified))
        {
            // Find an object state entry for a SalesOrderHeader object. 
            if (!entry.IsRelationship && (entry.Entity.GetType() == typeof(SalesOrderHeader)))
            {
                SalesOrderHeader orderToCheck = entry.Entity as SalesOrderHeader;

                // Call a helper method that performs string checking 
                // on the Comment property.
                string textNotAllowed = Validator.CheckStringForLanguage(
                    orderToCheck.Comment);

                // If the validation method returns a problem string, raise an error.
                if (textNotAllowed != string.Empty)
                {
                    throw new ArgumentException(String.Format("Changes cannot be "
                        + "saved because the {0} '{1}' object contains a "
                        + "string that is not allowed in the property '{2}'.",
                        entry.State, "SalesOrderHeader", "Comment"));
                }
            }
        }
    }
}

在此範例中，AdventureWorksProxy 類別的執行個體是用來變更 SalesOrderHeader 物件的 Comment 屬性。在 AdventureWorksProxy 類別提供的 ObjectContext 執行個體上呼叫 SaveChanges 時，會執行上一個範例中的驗證程式碼。

' Create an instance of the proxy class that returns an object context. 
Dim context As New AdventureWorksProxy()
' Get the first order from the context. 
Dim order As SalesOrderHeader = context.Context.SalesOrderHeaders.First()

' Add some text that we want to catch before saving changes. 
order.Comment = "some text"

Try
    ' Save changes using the proxy class. 
    Dim changes As Integer = context.Context.SaveChanges()
Catch ex As InvalidOperationException
    ' Handle the exception returned by the proxy class 
    ' validation if a problem string is found. 
    Console.WriteLine(ex.ToString())

// Create an instance of the proxy class that returns an object context.
AdventureWorksProxy context = new AdventureWorksProxy();
// Get the first order from the context.
SalesOrderHeader order =
    context.Context.SalesOrderHeaders.First();

// Add some text that we want to catch before saving changes.
order.Comment = "some text";

try
{
    // Save changes using the proxy class.
    int changes = context.Context.SaveChanges();
}
catch (InvalidOperationException ex)
{
    // Handle the exception returned by the proxy class
    // validation if a problem string is found.
    Console.WriteLine(ex.ToString());
}

此範例會對衍生自 ObjectContext 的 Proxy 類別中的物件進行變更，然後再呼叫 SaveChanges。此範例是用來叫用前面範例中所示範的事件處理。

Public Class AdventureWorksProxy
    ' Define the object context to be provided. 
    Private contextProxy As New AdventureWorksEntities()

    Public Sub New()
        ' When the object is initialized, register the 
        ' handler for the SavingChanges event. 
        AddHandler contextProxy.SavingChanges, AddressOf context_SavingChanges
    End Sub

    ' Method that provides an object context. 
    Public ReadOnly Property Context() As AdventureWorksEntities
        Get
            Return contextProxy
        End Get
    End Property

    ' SavingChanges event handler. 
    Private Sub context_SavingChanges(ByVal sender As Object, ByVal e As EventArgs)
        ' Ensure that we are passed an ObjectContext 
        Dim context As ObjectContext = TryCast(sender, ObjectContext)
        If context IsNot Nothing Then

            ' Validate the state of each entity in the context 
            ' before SaveChanges can succeed. 
            For Each entry As ObjectStateEntry In context.ObjectStateManager.GetObjectStateEntries(EntityState.Added Or EntityState.Modified)
                ' Find an object state entry for a SalesOrderHeader object. 
                If Not entry.IsRelationship AndAlso (entry.Entity.GetType() Is GetType(SalesOrderHeader)) Then
                    Dim orderToCheck As SalesOrderHeader = TryCast(entry.Entity, SalesOrderHeader)

                    ' Call a helper method that performs string checking 
                    ' on the Comment property. 
                    Dim textNotAllowed As String = Validator.CheckStringForLanguage(orderToCheck.Comment)

                    ' If the validation method returns a problem string, raise an error. 
                    If textNotAllowed <> String.Empty Then
                        Throw New ArgumentException(String.Format("Changes cannot be " & _
                                                                    "saved because the {0} '{1}' object contains a " & _
                                                                    "string that is not allowed in the property '{2}'.", _
                                                                    entry.State, "SalesOrderHeader", "Comment"))
                    End If
                End If
            Next
        End If
    End Sub
End Class

public class AdventureWorksProxy
{
    // Define the object context to be provided.
    private AdventureWorksEntities contextProxy =
        new AdventureWorksEntities();

    public AdventureWorksProxy()
    {
        // When the object is initialized, register the 
        // handler for the SavingChanges event.
        contextProxy.SavingChanges
            += new EventHandler(context_SavingChanges);
    }

    // Method that provides an object context.
    public AdventureWorksEntities Context
    {
        get
        {
            return contextProxy;
        }
    }

    // SavingChanges event handler.
    private void context_SavingChanges(object sender, EventArgs e)
    {
        // Ensure that we are passed an ObjectContext
        ObjectContext context = sender as ObjectContext;
        if (context != null)
        {

            // Validate the state of each entity in the context
            // before SaveChanges can succeed.
            foreach (ObjectStateEntry entry in
                context.ObjectStateManager.GetObjectStateEntries(
                EntityState.Added | EntityState.Modified))
            {
                // Find an object state entry for a SalesOrderHeader object. 
                if (!entry.IsRelationship && (entry.Entity.GetType() == typeof(SalesOrderHeader)))
                {
                    SalesOrderHeader orderToCheck = entry.Entity as SalesOrderHeader;

                    // Call a helper method that performs string checking 
                    // on the Comment property.
                    string textNotAllowed = Validator.CheckStringForLanguage(
                        orderToCheck.Comment);

                    // If the validation method returns a problem string, raise an error.
                    if (textNotAllowed != string.Empty)
                    {
                        throw new ArgumentException(String.Format("Changes cannot be "
                            + "saved because the {0} '{1}' object contains a "
                            + "string that is not allowed in the property '{2}'.",
                            entry.State, "SalesOrderHeader", "Comment"));
                    }
                }
            }
        }
    }
}

另請參閱

工作

HOW TO：在物件狀態變更時執行商務邏輯
 HOW TO：在純量屬性變更期間執行商務邏輯 (Entity Framework)
HOW TO：在關聯變更期間執行商務邏輯

概念

使用物件

HOW TO：在儲存變更時執行商務邏輯 (Entity Framework)

範例

另請參閱

工作

概念

其他資源