概述/描述
简单：多态删除从添加到 an 的运行时类型的对象不会TEntity引发方法ObjectSet<TEntity>返回的对象IBindingList.ListChanged上的事件。IBindingListObjectSet<TEntity>.IListSource.GetList()
但是，删除运行时类型匹配 的实例会在事件中TEntity得到有效通知。ListChanged
为了澄清，在任何时候，对象都有效地从底层集合或数据视图/存储中删除，但是当这些对象是严格派生自实际TEntity使用的类型的实例时，ListChanged不会引发事件来通知它们的删除。
为了对集合的运行时多态性提供适当的数据绑定支持，这只是一个惊人的 BUG。
复制
模型设置
- 每个类型策略的表。
- 实体模型在 Server 2012 Express 上针对生成的 SQL 数据库进行映射和验证。
这是实体层次结构（伪 UML）：
FiascoEntityContext : ObjectContext
+ Foos : ObjectSet<Foo>
Foo : EntityObject
+ Id: Int32
+ Name: String
SpecialFoo : Foo
+ SpecialProperty: String
示范代码
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Data.Objects;
namespace FiascoEF {
class Program {
static void Main(string[] args) {
using (FiascoEntityContext context = new FiascoEntityContext()) {
//
// add some foos
//
context.Foos.AddObject(new Foo { Name = "Foo1" });
context.Foos.AddObject(new BetterFoo { Name = "BetterFoo1", SpecialProperty = "Something Special" });
context.SaveChanges();
//
// show the contents
//
Console.WriteLine("Listing all foos:");
foreach (var foo in context.Foos) {
Console.WriteLine(" Got {0}: Id={1} Name={2} (State={3})", foo, foo.Id, foo.Name, foo.EntityState);
}
//
// attach handler for the ListChanged event of the IBindingList returned by context.Foos as IListSource
// NOTE: have to do this here bacause SaveChanges() above will reset the internal IBindingList
//
var bindingList = (context.Foos as IListSource).GetList() as IBindingList;
bindingList.ListChanged += new ListChangedEventHandler(bindingList_ListChanged);
//
// delete all foos and show state. expect the event handler above to be invoked.
//
Console.WriteLine("Deleting all foos:");
foreach (var foo in context.Foos) {
context.Foos.DeleteObject(foo);
Console.WriteLine(" Deleted {0}: Id={1} Name={2} (State={3})", foo, foo.Id, foo.Name, foo.EntityState);
}
context.SaveChanges();
}
}
static void bindingList_ListChanged(object sender, ListChangedEventArgs e) {
Console.WriteLine(" Event on {0}: {1}", sender, e.ListChangedType);
}
}
}
预期成绩
Listing all foos:
Got FiascoEF.Foo: Id=257 Name=Foo1 (State=Unchanged)
Got FiascoEF.BetterFoo: Id=258 Name=BetterFoo1 (State=Unchanged)
Deleting all foos:
Event on System.Data.Objects.ObjectView`1[FiascoEF.Foo]: ItemDeleted
Deleted FiascoEF.Foo: Id=257 Name=Foo1 (State=Deleted)
Event on System.Data.Objects.ObjectView`1[FiascoEF.Foo]: ItemDeleted
Deleted FiascoEF.BetterFoo: Id=258 Name=BetterFoo1 (State=Deleted)
实际结果
Listing all foos:
Got FiascoEF.Foo: Id=257 Name=Foo1 (State=Unchanged)
Got FiascoEF.BetterFoo: Id=258 Name=BetterFoo1 (State=Unchanged)
Deleting all foos:
Event on System.Data.Objects.ObjectView`1[FiascoEF.Foo]: ItemDeleted
Deleted FiascoEF.Foo: Id=257 Name=Foo1 (State=Deleted)
Deleted FiascoEF.BetterFoo: Id=258 Name=BetterFoo1 (State=Deleted)
研究
通过反射器发现实际IBindingList返回的是一个类型ObjectView<TElement>，并且这个类型将移除操作委托给了一个内部IObjectViewData<TElement>。为该接口找到的实现ObjectViewQueryResultData<TElement>定义：
public ListChangedEventArgs OnCollectionChanged(object sender, CollectionChangeEventArgs e, ObjectViewListener listener) {
ListChangedEventArgs changeArgs = null;
if (e.Element.GetType().IsAssignableFrom(typeof(TElement)) && _bindingList.Contains((TElement) (e.Element))) {
...
changeArgs = new ListChangedEventArgs(ListChangedType.ItemDeleted, ...);
...
}
return changeArgs;
}
支票：
if (e.Element.GetType().IsAssignableFrom(typeof(TElement)) && ...) { ... }
似乎是假的......可能是以下意图？
if (typeof(TElement).IsAssignableFrom(e.Element.GetType()) && ...) { ... }