精進不休 .NET 4.0 (8)：ADO.NET Entity Framework 4.0 Self-Tracking Entity 與 WCF 整合

新功能概覽

• Self-Tracking Entity (STE)：基於 POCO，實體自身追蹤狀態（Added/Modified/Deleted），適用於 N-Tier 架構。
• WCF 整合 STE：跨層傳遞實體時自動攜帶狀態，伺服端直接 ApplyChanges 即可同步資料庫。

範例 1：純 STE 單表 CRUD

BLL.cs

public class BLL
{
    public List<ProductCategory> GetCategories()
    {
        using (var ctx = new SelfTrackingEntities())
            return ctx.ProductCategories.ToList();
    }

    public ProductCategory GetCategory(int id)
    {
        using (var ctx = new SelfTrackingEntities())
            return ctx.ProductCategories.Single(c => c.ProductCategoryID == id);
    }

    public void UpdateCategory(ProductCategory cat)
    {
        using (var ctx = new SelfTrackingEntities())
        {
            ctx.ProductCategories.ApplyChanges(cat);
            ctx.SaveChanges();
        }
    }

    public void DeleteCategory(ProductCategory cat)
    {
        cat.MarkAsDeleted();
        UpdateCategory(cat);
    }

    public void AddCategory(ProductCategory cat)
    {
        UpdateCategory(cat); // 新增也走 ApplyChanges
    }
}

Demo.aspx.cs 關鍵：手動 StartTracking

protected void ListView1_ItemUpdating(object sender, ListViewUpdateEventArgs e)
{
    var bll = new BLL();
    var cat = bll.GetCategory((int)ListView1.DataKeys[e.ItemIndex].Value);
    cat.StartTracking(); // 非 WCF 情境必須手動呼叫
    cat.Name = e.NewValues["Name"].ToString();
    bll.UpdateCategory(cat);
    ListView1.EditIndex = -1;
    e.Cancel = true;
}

範例 2：WCF 服務端與客戶端整合 STE

服務合約 IMyService.cs

[ServiceContract]
public interface IMyService
{
    [OperationContract] List<ProductCategory> GetCategories();
    [OperationContract] ProductCategory GetCategory(int categoryId);
    [OperationContract] int UpdateCategory(ProductCategory category);
    [OperationContract] int AddCategory(ProductCategory category);
    [OperationContract] int DeleteCategory(int categoryId);
}

服務實作 MyService.cs

public class MyService : IMyService
{
    public int UpdateCategory(ProductCategory category)
    {
        using (var ctx = new AdventureWorksEntities())
        {
            ctx.ProductCategories.ApplyChanges(category);
            ctx.ObjectStateManager.ChangeObjectState(category, EntityState.Modified);
            return ctx.SaveChanges();
        }
    }

    public int AddCategory(ProductCategory category)
    {
        using (var ctx = new AdventureWorksEntities())
        {
            ctx.ProductCategories.ApplyChanges(category);
            return ctx.SaveChanges();
        }
    }

    public int DeleteCategory(int categoryId)
    {
        using (var ctx = new AdventureWorksEntities())
        {
            var cat = GetCategory(categoryId);
            cat.MarkAsDeleted(); // 先標記再 ApplyChanges
            ctx.ProductCategories.ApplyChanges(cat);
            return ctx.SaveChanges();
        }
    }
    // GetCategories/GetCategory 略...
}

客戶端 Demo.aspx.cs

private void BindData()
{
    var svc = new ChannelFactory<IMyService>("BasicHttpBinding_IMyService").CreateChannel();
    ListView1.DataSource = svc.GetCategories();
    ListView1.DataBind();
}

protected void ListView1_ItemUpdating(object sender, ListViewUpdateEventArgs e)
{
    var svc = new MyServiceClient();
    var cat = svc.GetCategory((int)ListView1.DataKeys[e.ItemIndex].Value);
    cat.Name = (string)e.NewValues["Name"];
    svc.UpdateCategory(cat);
    BindData();
}
// Insert/Delete/Cancel/Edit 類似...

STE 關鍵差異

總結

STE 解決了 N-Tier 架構下實體狀態同步難題，配合 WCF 讓伺服端極簡單地持久化離線實體圖，是 EF 4.0 企業級應用的重要特性。