我正在编写一个WPF应用程序，使用MVVM设计和Entity Framework 4作为ORM。我在视图模型中有集合属性，这些属性将包含从业务层提交的查询响应中作为IEnumerable 集合返回的实体集合。
我希望简单地将IEnumerable 结果集包装在ObservableCollection 中。然而，我发现自己在存储库中编写了更改跟踪代码，或者维护了更改对象的影子集合，以保持视图模型和持久性层同步。每当实体添加到视图模型中的集合中时，我都必须去我的存储库将其添加到EF4 ObjectSet中。我必须在更新和删除方面做同样的事情。
为了简化事情，我从CodePlex（http://waf.codeplex.com/）的WPF Application Framework项目中借用了一个EdmObservableCollection 类。该类用EF4 ObjectContext的引用包装了一个ObservableCollection ，因此可以在更新集合时更新OC。我在下面重新打印了EdmObservableCollection类。该类工作得很好，但它有一点代码气味，因为我最终在我的视图模型中引用了EF4。
我的问题是：在WPF应用程序中，保持EF4实体集合与其对象上下文同步的通常方法是什么？ EdmObservableCollection是否是合适的方法，还是有更好的方法？我在使用EF4方面是否遗漏了一些基本内容？感谢您的帮助。
我希望简单地将IEnumerable 结果集包装在ObservableCollection 中。然而，我发现自己在存储库中编写了更改跟踪代码，或者维护了更改对象的影子集合，以保持视图模型和持久性层同步。每当实体添加到视图模型中的集合中时，我都必须去我的存储库将其添加到EF4 ObjectSet中。我必须在更新和删除方面做同样的事情。
为了简化事情，我从CodePlex（http://waf.codeplex.com/）的WPF Application Framework项目中借用了一个EdmObservableCollection 类。该类用EF4 ObjectContext的引用包装了一个ObservableCollection ，因此可以在更新集合时更新OC。我在下面重新打印了EdmObservableCollection类。该类工作得很好，但它有一点代码气味，因为我最终在我的视图模型中引用了EF4。
我的问题是：在WPF应用程序中，保持EF4实体集合与其对象上下文同步的通常方法是什么？ EdmObservableCollection是否是合适的方法，还是有更好的方法？我在使用EF4方面是否遗漏了一些基本内容？感谢您的帮助。
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Data.Objects;
using System.Linq;
namespace Ef4Sqlce4Demo.ViewModel.BaseClasses
{
/// <summary>
/// An ObservableCollection for Entity Framework 4 entity collections.
/// </summary>
/// <typeparam name="T">The type of EF4 entity served.</typeparam>
/// <remarks>Developed from WPF Application Framework (WAF) http://waf.codeplex.com/</remarks>
public class EdmObservableCollection<T> : ObservableCollection<T>
{
#region Fields
// Member variables
private readonly string m_EntitySetName;
private readonly ObjectContext m_ObjectContext;
#endregion
#region Constructors
/// <summary>
/// Creates a new EDM Observable Collection and populates it with a list of items.
/// </summary>
/// <param name="objectContext">The EF4 ObjectContext that will manage the collection.</param>
/// <param name="entitySetName">The name of the entity set in the EDM.</param>
/// <param name="items">The items to be inserted into the collection.</param>
public EdmObservableCollection(ObjectContext objectContext, string entitySetName, IEnumerable<T> items)
: base(items ?? new T[] {})
{
if (objectContext == null)
{
throw new ArgumentNullException("objectContext");
}
if (entitySetName == null)
{
throw new ArgumentNullException("entitySetName");
}
m_ObjectContext = objectContext;
m_EntitySetName = entitySetName;
}
/// <summary>
/// Creates an empty EDM Observable Collection that has an ObjectContext.
/// </summary>
/// <param name="objectContext">The EF4 ObjectContext that will manage the collection.</param>
/// <param name="entitySetName">The name of the entity set in the EDM.</param>
public EdmObservableCollection(ObjectContext objectContext, string entitySetName)
: this(objectContext, entitySetName, null)
{
}
/// <summary>
/// Creates an empty EDM Observable Collection, with no ObjectContext.
/// </summary>
/// <remarks>
/// We use this constructor to create a placeholder collection before we have an
/// ObjectContext to work with. This state occurs when the program is first launched,
/// before a file is open. We need to initialize collections in the application's
/// ViewModels, so that the MainWindow can get Note and Tag counts, which are zero.
/// </remarks>
public EdmObservableCollection()
{
}
#endregion
#region Method Overrides
protected override void InsertItem(int index, T item)
{
base.InsertItem(index, item);
m_ObjectContext.AddObject(m_EntitySetName, item);
}
protected override void RemoveItem(int index)
{
T itemToDelete = this[index];
base.RemoveItem(index);
m_ObjectContext.DeleteObject(itemToDelete);
}
protected override void ClearItems()
{
T[] itemsToDelete = this.ToArray();
base.ClearItems();
foreach (T item in itemsToDelete)
{
m_ObjectContext.DeleteObject(item);
}
}
protected override void SetItem(int index, T item)
{
T itemToReplace = this[index];
base.SetItem(index, item);
m_ObjectContext.DeleteObject(itemToReplace);
m_ObjectContext.AddObject(m_EntitySetName, item);
}
#endregion
#region Public Methods
/// <summary>
/// Adds an object to the end of the collection.
/// </summary>
/// <param name="item">The object to be added to the end of the collection.</param>
public new void Add(T item)
{
InsertItem(Count, item);
}
/// <summary>
/// Removes all elements from the collection.
/// </summary>
/// <param name="clearFromContext">Whether the items should also be deleted from the ObjectContext.</param>
public void Clear(bool clearFromContext)
{
if (clearFromContext)
{
foreach (T item in Items)
{
m_ObjectContext.DeleteObject(item);
}
}
base.Clear();
}
/// <summary>
/// Inserts an element into the collection at the specified index.
/// </summary>
/// <param name="index">The zero-based index at which item should be inserted.</param>
/// <param name="item">The object to insert.</param>
public new void Insert(int index, T item)
{
base.Insert(index, item);
m_ObjectContext.AddObject(m_EntitySetName, item);
}
/// <summary>
/// Updates the ObjectContext for changes to the collection.
/// </summary>
public void Refresh()
{
m_ObjectContext.SaveChanges();
}
/// <summary>
/// Removes the first occurrence of a specific object from the collection.
/// </summary>
/// <param name="item">The object to remove from the collection.</param>
public new void Remove(T item)
{
base.Remove(item);
m_ObjectContext.DeleteObject(item);
}
#endregion
}
}