HOW TO：定義自訂物件內容 (Entity Framework)

當您使用 POCO 實體，會停用 Entity Framework 的物件層產生。 除了定義自訂實體類型，您必須透過手動建立的 EntityConnection 的執行個體 (您傳遞給 ObjectContext 之建構函式的執行個體)，定義自訂物件內容類型或管理您自己的連接。 如需如何建立 EntityConnection 的詳細資訊，請參閱 HOW TO：建立 EntityConnection 連接字串 (Entity Framework)。

本主題也將示範如何建立自訂物件內容。

注意：
若要使用 ADO.NET Entity Data Model Designer (Entity Designer) 來停用物件層的產生，請在 Entity Designer 中開啟 .edmx 檔案。以滑鼠右鍵按一下設計工具介面並選取 [屬性]。在 [屬性] 視窗中，選取 [程式碼產生策略] 屬性並選取 [None]。

自訂物件內容類別會管理 HOW TO：定義 POCO 實體 (Entity Framework)中所定義的 POCO 實體。

自訂物件內容應該包含下列功能：

• 具現化您的概念模型特有之 ObjectContext (包括預先定義的連接) 的功能。

• 可傳回型別特有 ObjectSet 物件的屬性。

如需定義自訂實體類型的詳細資訊，請參閱 HOW TO：定義 POCO 實體 (Entity Framework)。

在自訂物件內容程式碼中使用產生的物件內容程式碼

1. 將類別程式碼檔加入至您的專案。

2. 包含下列命名空間：

   System

   System.Data.Objects

   System.Collections.Generic

3. 將類別重新命名為 POCOAdventureWorksEntities。 請確定類別繼承自 ObjectContext 類別。

   Partial Public Class POCOAdventureWorksEntities
       Inherits ObjectContext
   

   public partial class POCOAdventureWorksEntities : ObjectContext
   

4. 為每個 POCO 實體類型定義 ObjectSet 類型的成員變數：

   Private _contacts As ObjectSet(Of Contact)
   Private _lineItems As ObjectSet(Of LineItem)
   Private _orders As ObjectSet(Of Order)
   

   private ObjectSet<Contact> _contacts;
   private ObjectSet<LineItem> _lineItems;
   private ObjectSet<Order> _orders;
   

5. 定義 POCOAdventureWorksEntities 類別的建構函式。

   Public Sub New()
       MyBase.New("name=AdventureWorksEntities", "AdventureWorksEntities")
       Me.ContextOptions.LazyLoadingEnabled = True
   End Sub
   
   Public Sub New(ByVal connectionString As String)
       MyBase.New(connectionString, "AdventureWorksEntities")
       Me.ContextOptions.LazyLoadingEnabled = True
   End Sub
   

    public POCOAdventureWorksEntities()
        : base("name=AdventureWorksEntities", "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
   }
   
    public POCOAdventureWorksEntities(string connectionString)
        : base(connectionString, "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
    }
   

6. 定義會傳回 ObjectSet 物件的屬性。

   Public ReadOnly Property Contacts() As ObjectSet(Of Contact)
       Get
           Return If(_contacts, MyBase.CreateObjectSet(Of Contact)())
       End Get
   End Property
   
   Public ReadOnly Property LineItems() As ObjectSet(Of LineItem)
       Get
           Return If(_lineItems, MyBase.CreateObjectSet(Of LineItem)())
       End Get
   End Property
   
   Public ReadOnly Property Orders() As ObjectSet(Of Order)
       Get
           Return If(_orders, MyBase.CreateObjectSet(Of Order)())
       End Get
   End Property
   

   public ObjectSet<Contact> Contacts
   {
       get
       {
           return _contacts ?? (_contacts = base.CreateObjectSet<Contact>());
       }
   }
   
   public ObjectSet<LineItem> LineItems
   {
       get
       {
           return _lineItems ?? (_lineItems = base.CreateObjectSet<LineItem>());
       }
   }
   
   public ObjectSet<Order> Orders
   {
       get
       {
           return _orders ?? (_orders = base.CreateObjectSet<Order>());
       }
   }
   

範例

這個範例會說明支援 Contact、Order 和 LineItem 自訂資料類別的自訂物件內容程式碼。

Partial Public Class POCOAdventureWorksEntities
    Inherits ObjectContext
    Private _contacts As ObjectSet(Of Contact)
    Private _lineItems As ObjectSet(Of LineItem)
    Private _orders As ObjectSet(Of Order)
#Region "Constructors"
    Public Sub New()
        MyBase.New("name=AdventureWorksEntities", "AdventureWorksEntities")
        Me.ContextOptions.LazyLoadingEnabled = True
    End Sub

    Public Sub New(ByVal connectionString As String)
        MyBase.New(connectionString, "AdventureWorksEntities")
        Me.ContextOptions.LazyLoadingEnabled = True
    End Sub
#End Region

#Region "ObjectSet Properties"
    Public ReadOnly Property Contacts() As ObjectSet(Of Contact)
        Get
            Return If(_contacts, MyBase.CreateObjectSet(Of Contact)())
        End Get
    End Property

    Public ReadOnly Property LineItems() As ObjectSet(Of LineItem)
        Get
            Return If(_lineItems, MyBase.CreateObjectSet(Of LineItem)())
        End Get
    End Property

    Public ReadOnly Property Orders() As ObjectSet(Of Order)
        Get
            Return If(_orders, MyBase.CreateObjectSet(Of Order)())
        End Get
    End Property

#End Region
    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

End Class

public partial class POCOAdventureWorksEntities : ObjectContext
{
    private ObjectSet<Contact> _contacts;
    private ObjectSet<LineItem> _lineItems;
    private ObjectSet<Order> _orders;
    #region Constructors
    public POCOAdventureWorksEntities()
        : base("name=AdventureWorksEntities", "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
   }

    public POCOAdventureWorksEntities(string connectionString)
        : base(connectionString, "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
    }
    #endregion

    #region ObjectSet Properties
    public ObjectSet<Contact> Contacts
    {
        get
        {
            return _contacts ?? (_contacts = base.CreateObjectSet<Contact>());
        }
    }

    public ObjectSet<LineItem> LineItems
    {
        get
        {
            return _lineItems ?? (_lineItems = base.CreateObjectSet<LineItem>());
        }
    }

    public ObjectSet<Order> Orders
    {
        get
        {
            return _orders ?? (_orders = base.CreateObjectSet<Order>());
        }
    }

    #endregion
    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);
    }

}

另請參閱

參考

EDM 產生器 (EdmGen.exe)

概念

自訂物件 (Entity Framework)

其他資源

How to: Customize Object-Layer Code Generation