使用DbContext刷新实体实例

Question

使用EF4 CTP5 DbContext,相当于此

    public void Refresh(Document instance)
    {
        _ctx.Refresh(RefreshMode.StoreWins, instance);
    }

我已经尝试过了,但它不会做同样的事情,更新实例

    public void Refresh(Document instance)
    {
        _ctx.ChangeTracker.DetectChanges();
    }

？

Answer 1

你必须使用这个:

public void Refresh(Document instance)
{
  _ctx.Entry<Document>(instance).Reload();
}

Answer 2

以上不起作用.Reload()方法无法从数据库中正确刷新实体.它执行SQL选择查询,但不构建导航属性的代理.请参阅下面的示例(我使用带有EF 5.1的SQL Server中的Northwind数据库):

NorthwindEntities northwindEntities = new NorthwindEntities();
Product newProduct = new Product
{
    ProductName = "new product",
    Discontinued = false,
    CategoryID = 3
};
northwindEntities.Products.Add(newProduct);
northwindEntities.SaveChanges();

// Now the product is stored in the database. Let's print its category

Console.WriteLine(newProduct.Category); // prints "null" -> navigational property not loaded

// Find the product by primary key --> returns the same object (unmodified)
// Still prints "null" (due to caching and identity resolution)
var productByPK = northwindEntities.Products.Find(newProduct.ProductID);
Console.WriteLine(productByPK.Category); // null (due to caching)

// Reloading the entity from the database doesn't help!
northwindEntities.Entry<Product>(newProduct).Reload();
Console.WriteLine(newProduct.Category); // null (reload doesn't help)

// Detach the object from the context
((IObjectContextAdapter)northwindEntities).ObjectContext.Detach(newProduct);

// Now find the product by primary key (detached entities are not cached)
var detachedProductByPK = northwindEntities.Products.Find(newProduct.ProductID);
Console.WriteLine(detachedProductByPK.Category); // works (no caching)

我可以得出结论,EF实体的真正刷新/重载可以通过Detach + Find来完成:

((IObjectContextAdapter)context).ObjectContext.Detach(entity);
entity = context.<SomeEntitySet>.Find(entity.PrimaryKey);

Nakov