如何：定义自定义对象上下文（实体框架）

项目
02/28/2011

在使用 POCO 实体时，可通过实体框架禁用对象层生成。除定义自定义实体类型外，还需要通过您传递到 ObjectContext 的构造函数的 EntityConnection 的手动创建实例，来定义自定义对象上下文类型或管理您自己的连接。有关如何创建 EntityConnection 的信息，请参见如何：生成 EntityConnection 连接字符串（实体框架）。

本主题演示如何创建自定义对象上下文。

注意：
若要使用 ADO.NET Entity Data Model Designer（实体设计器）禁用对象层生成，请在实体设计器中打开 .edmx 文件。右击设计器图面并选择“属性”。在“属性”窗口中选择“代码生成策略”属性，并选择 None。

自定义对象上下文类管理如何：定义 POCO 实体（实体框架）中定义的 POCO 实体。

自定义对象上下文应包含以下功能：

实例化概念模型特定的 ObjectContext（包括预定义连接）的能力。
返回特定于类型的 ObjectSet 对象的属性。

有关定义自定义实体类型的信息，请参见如何：定义 POCO 实体（实体框架）。

使用自定义对象上下文代码中的生成的对象上下文代码

将类代码文件添加到项目中。
包括以下命名空间：

System

System.Data.Objects

System.Collections.Generic

将该类重命名为 POCOAdventureWorksEntities。确保类继承自 ObjectContext 类。

Partial Public Class POCOAdventureWorksEntities
    Inherits ObjectContext

public partial class POCOAdventureWorksEntities : ObjectContext

为每个 POCO 实体类型定义 ObjectSet 类型的成员变量：

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;

定义对 POCOAdventureWorksEntities 类的构造函数。

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;
 }

定义返回 ObjectSet 对象的属性。

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>());
    }
}

示例

本示例演示支持 Contact、Order、和 LineItem 自定义数据类的自定义对象上下文代码。

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);
    }

}

另请参见

通过

如何：定义自定义对象上下文（实体框架）

使用自定义对象上下文代码中的生成的对象上下文代码

示例

另请参见

参考

概念

其他资源

其他资源