C# 如何从新创建的分离实体更新实体

假设我创建了一个新产品，如下所示：

Product p=new Product(){ Id= 2,Name="some name"};

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我的产品变量从未附加到数据上下文，如何附加此实体，以便数据库中Id=2的现有产品使用我分离的产品的名称进行更新？

我希望类似的方法也能奏效

 Datacontext db = new Datacontext(); // replace with your DataContext
 Product originalProduct = 
         db.Products.Single(p => p.Id == 2); // get product with Id 2

 originalProduct.Name = "SomeName";  // only reset Name prop
 originalProduct = p;                // or you may assign p to originalProduct
 db.SubmitChanges();                 // submit changes to DB

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更简单的解决方案是在您希望这样工作的实体上实现

ICloneable

接口。然后，您只需将Clone（）调用到从数据库中提取的“原始”实体中

例如：

class Product : ICloneable
{
    public virtual int Id { get; private set; }
    public virtual string Name { get; set; }

    public object Clone()
    {
        return new Product() { Id=this.Id, Name=this.Name };
    }
}

然后你需要做的就是：

Datacontext db = new Datacontext(); // replace with your DataContext
Product originalProduct = 
        db.Products.Single(p => p.Id == 2); // get product with Id 2

db.originalProduct = p.Clone()
db.SubmitChanges();

编辑： 我在工作中遇到了同样的问题，到目前为止，我找到的最优雅的解决方案是构建一个扩展方法，该方法接收新创建的实体（在您的例子中是

产品

），并将其属性（标识符除外）复制到从DataContext中提取的实体

我通过反射复制了所有属性，这样，如果我更新了实体，那么扩展方法仍然有效

希望这对你也有帮助

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如果你能找到一个更优雅的方法来解决这个问题，我想听听：）

再加上gillyb的帖子和我留下的评论。克隆实体的一种非常简单的方法是：

Private Function CloneEntity(Of TEntity)(ByVal entity As TEntity) As TEntity

    Dim dataContext As New DataContext()
    Dim entityType As System.Type = GetType(TEntity)

    ' If the purpose of the clone is just to attach it the existing entity to a new
    ' DataContext, you can use IdentityMembers in place of PersistantDataMembers. Setting
    ' only the IdentityMembers is enough to allow for attaching the clone as an "originaL"
    ' entity to the DataContext.
    Dim dataMembers = dataContext.Mapping.GetTable(entityType).RowType.PersistentDataMembers

    Dim clone As TEntity ' Do something here to create an entity of the desired type. 
    Dim boxedClone As Object = clone

    For Each dm In dataMembers

         ' Depending on how your ColumnAttribute is set, you would use StorageAccessor if
         ' the Storage property is set. Otherwise, you would use MemberAccessor instead.
          dm.StorageAccessor.SetBoxedValue(boxedClone, dm.StorageAccessor.GetBoxedValue(entity))
    Next

    Return clone

End Function

Dim dataContext As New DataContext()
dataContext.GetTable(Of Object)().Attach(entityToUpdate, CloneEntity(entityToUpdate))
dataContext.SubmitChanges()

那么您只需要执行以下操作：

Private Function CloneEntity(Of TEntity)(ByVal entity As TEntity) As TEntity

    Dim dataContext As New DataContext()
    Dim entityType As System.Type = GetType(TEntity)

    ' If the purpose of the clone is just to attach it the existing entity to a new
    ' DataContext, you can use IdentityMembers in place of PersistantDataMembers. Setting
    ' only the IdentityMembers is enough to allow for attaching the clone as an "originaL"
    ' entity to the DataContext.
    Dim dataMembers = dataContext.Mapping.GetTable(entityType).RowType.PersistentDataMembers

    Dim clone As TEntity ' Do something here to create an entity of the desired type. 
    Dim boxedClone As Object = clone

    For Each dm In dataMembers

         ' Depending on how your ColumnAttribute is set, you would use StorageAccessor if
         ' the Storage property is set. Otherwise, you would use MemberAccessor instead.
          dm.StorageAccessor.SetBoxedValue(boxedClone, dm.StorageAccessor.GetBoxedValue(entity))
    Next

    Return clone

End Function

Dim dataContext As New DataContext()
dataContext.GetTable(Of Object)().Attach(entityToUpdate, CloneEntity(entityToUpdate))
dataContext.SubmitChanges()

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这肯定会起作用，但总是复制属性可能会很痛苦。在NHibernate中，他们有一个名为RETACH的构造，可以让您指定它是DB中的一个现有对象，我不确定L2S是否有这个。DB.originalProduct似乎不正确。。。当您将p.Clone（）分配给originalProduct时，它将不再“附加”到上下文，因此它将不会被持久化。哦，您是对的，我没有完全考虑清楚。。。我会检查一下并试着修复它。我在工作中遇到了同样的问题，所以我需要想出一个好的解决方案，当我这样做的时候，我会解决它的！：）谢谢如果要跳过使用反射，还可以使用DataContext的MappingSource将值复制到新的克隆版本。这样，它只会复制特定于数据库的属性。另外，我认为您正在寻找DataContext.GetTable（）.Attach（原始，新）在这里。没问题！我将把我用作另一个答案的代码发布到您的答案上：）