EntitySet与EntityList到底有什么本质区别？各自最恰当的使用场合是？

[xhtmldivcss]

public class EntityList<T> : ObservableCollection<T> where T : global::System.ServiceModel.DomainServices.Client.Entity

public class ObservableCollection<T> : Collection<T>, INotifyCollectionChanged, INotifyPropertyChanged

public sealed class EntitySet<TEntity> : EntitySet, IEnumerable<TEntity>, IEnumerable, ICollectionViewFactory where TEntity : global::System.ServiceModel.DomainServices.Client.Entity

public abstract class EntitySet : IEnumerable, INotifyCollectionChanged, IRevertibleChangeTracking, IChangeTracking, INotifyPropertyChanged

从以上可以看出：
1、EntitySet和EntityList都实现了我们经常关注的INotifyPropertyChanged和INotifyCollectionChanged.

2、EntityList是个ObservableCollection.

3、EntityList有个Source属性。

4、从EntityList的构造函数可以看出它backed by an EntitySet.

public EntityList(EntitySet<T> entitySet);
//
// Summary:
//     Initializes a new instance of the Microsoft.Windows.Data.DomainServices.EntityList<T>
//     with the specified source
//
// Parameters:
//   entitySet:
//     The System.ServiceModel.DomainServices.Client.EntitySet<TEntity> that backs
//     this list. All items added or removed from this list will also be added or
//     removed from the backing Microsoft.Windows.Data.DomainServices.EntityList<T>.EntitySet.
//
//   source:
//     The source collection used to populate this list
public EntityList(EntitySet<T> entitySet, IEnumerable<T> source);

那么除了经常作为DomainCollectionView(loader, source);中的source部分之外，EntityList<T>到底有什么主要作用？

[xhtmldivcss]

暂时不管DomainCollectionView了。

用简单的代码做比较。
默认读取ProductID为1和2的二条记录，点击界面按钮执行LoadMoreProducts命令时（这回读取ProductID为1和3的记录），控件绑定EntityList<T>和EntitySet<T>的结果不一样。绑定EntitySet<T>时，显示1、2、3三条记录。绑定EntityList<T>时，只显示1、3二条记录。

public class ProductsViewModel : NotificationObject
{
    private NorthwindDomainContext _Context = new NorthwindDomainContext();

    public ICommand LoadMoreProducts
    {
        get
        {
            return new DelegateCommand(OnLoadMoreProducts);
        }
    }
    public ICommand SaveChanges
    {
        get
        {
            return new DelegateCommand(OnSave);
        }
    }
    void OnSave()
    {
        _Context.SubmitChanges();
    }
        

    void OnLoadMoreProducts()
    {
        //_Context.Products.Clear();
            
        EntityQuery<Product> query = _Context.GetProductsQuery();
        //query = query.Where(p => p.ProductID == 3 || p.ProductID == 4);
        query = from p in query
                where p.ProductID == 1 || p.ProductID == 3
                select p;


        _Context.Load(query, LoadBehavior.MergeIntoCurrent, OnLoadProductsCompleted, null);
    }
    //当界面控件绑定EntityList<Products>时，执行LoadMoreProducts命令的结果是
    //ProductID为1、2、3的三个记录。
    public EntitySet<Product> Products
    {
        get
        {
            return _Context.Products;
        }
    }
    //当界面控件绑定EntityList<Product>时，执行LoadMoreProducts命令的结果是
    //ProductID为1、3的二条记录。
    public EntityList<Product> _productList;
    public EntityList<Product> ProductList
    {
        get 
        {
            if(_productList == null)
                _productList = new EntityList<Product>(Products);

            return _productList;
        }
    }

    public ProductsViewModel()
    {
        if (!DesignerProperties.IsInDesignTool)
        {
            EntityQuery<Product> query = _Context.GetProductsQuery();
            query = query.Where(p => p.ProductID == 1 || p.ProductID == 2);
            _Context.Load(query, LoadBehavior.RefreshCurrent, OnLoadProductsCompleted, null);
        }

    }
    void OnLoadProductsCompleted(LoadOperation<Product> lo)
    {
        if (lo.HasError)
        {
            MessageBox.Show(lo.Error.Message);
            lo.MarkErrorAsHandled();
        }
        else if (!lo.IsCanceled)
        { 
            ProductList.Source = lo.Entities;
        }
            
    }

}

我觉得应该有个很关键的地方没想明白。哪位能指点一下，谢谢。

[xhtmldivcss]

说来也非常简单。每次DomainContext.Load不同数据的时候，EntitySet<T>会不停地累加新数据。比如一开始Load前2个对象，再Load2个不同数据时，EntitySet<T>里会有4个记录，而EntityList<T>只会显示最后Load的那些数据。

//ViewModel
public class ProductsViewModel : NotificationObject
{
    private int id = 1;
    private NorthwindDomainContext _Context = new NorthwindDomainContext();
    public ProductsViewModel()
    {
        if (!DesignerProperties.IsInDesignTool)
        {
            IsBusy = true;
            EntityQuery<Product> query = _Context.GetProductsQuery();
            query = from p in query
                    where p.ProductID == id || p.ProductID == (id + 1)
                    select p;

            _Context.Load(query, LoadBehavior.MergeIntoCurrent, OnLoadProductsCompleted, null);
        }
    }
    public ICommand LoadMoreProducts
    {
        get
        {
            return new DelegateCommand(OnLoadMoreProducts);
        }
    }
    // 左侧DataGrid绑定EntitySet<Product>
    public EntitySet<Product> Products
    {
        get { return _Context.Products; }
    }
    private EntityList<Product> _productsList;
    // 右侧DataGrid绑定EntityList<Product>
    public EntityList<Product> ProductsList
    {
        get
        {
            if (_productsList == null)
                _productsList = new EntityList<Product>(Products);

            return _productsList;
        }
    }
    void OnLoadMoreProducts()
    {
        IsBusy = true;
        EntityQuery<Product> query = _Context.GetProductsQuery();
        query = from p in query
                where p.ProductID == id || p.ProductID == (id + 1)
                select p;

        _Context.Load(query, LoadBehavior.MergeIntoCurrent, OnLoadProductsCompleted, null);
    }
    private bool _isBusy = false;
    public bool IsBusy
    {
        get
        {
            return _isBusy;
        }
        set
        {
            if (_isBusy != value)
            {
                _isBusy = value;
                RaisePropertyChanged(() => this.IsBusy);
            }
        }
    }

    void OnLoadProductsCompleted(LoadOperation<Product> lo)
    {
        IsBusy = false;

        if (lo.HasError)
        {
            MessageBox.Show(lo.Error.Message);
            lo.MarkErrorAsHandled();
        }
        else if (!lo.IsCanceled)
        {
            id++;
            ProductsList.Source = lo.Entities;
        }
    }
}

开始时：


当点击Load More Products按钮，读取的是ProductID为2、3时界面：

[xhtmldivcss]

谁回一个，好让我回收点可用分……

[哀]

囧，这么没人气啊 都没人回复。

[mibbadman]

[net_friends]

[小基]

[haitang59]

[zhu6789888]

[Louis-Lv]

来接分了

[xiongyu2006]

我靠，这不是技术帖吗？

[山之魂2]

顶楼主，本人末有研究得这么细

[xh308]