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

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 OnContextCreatedObjectContext 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 AddedModified 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