linq - 无法强制 LINQ 评估

Question

如果页面上发生错误，我正在尝试获取记录并将其存储以供以后使用。

此代码用于创建/编辑。所以我从视图模型中获取值并映射到数据库实体：

Dim objExistingSupplier As SUPPLIER = db.SUPPLIER.Single(Function(e) e.SUPPLIER_ID = Supplier.SUPPLIER_ID)
objPermStaffAction = objExistingSupplier
objSupplier = Mapper.Map(Of SupplierViewModel, SUPPLIER)(Supplier, objExistingSupplier)

据我了解， .Single 应该强制评估。但是，映射发生后，objPermStaffAction 对象中的属性会丢失/更改。有人可以解释我做错了什么吗？

这是整个功能：

    Private Function SaveSupplier(Supplier As SupplierViewModel) As ActionResult
        Dim objSupplier, objPermStaffAction As SUPPLIER
        If Supplier.SUPPLIER_ID = 0 Then
            objSupplier = Mapper.Map(Of SupplierViewModel, SUPPLIER)(Supplier)
        Else
            Dim objExistingSupplier As SUPPLIER = db.SUPPLIER.Single(Function(e) e.SUPPLIER_ID = Supplier.SUPPLIER_ID)
            objPermStaffAction = objExistingSupplier
            objSupplier = Mapper.Map(Of SupplierViewModel, SUPPLIER)(Supplier, objExistingSupplier)
        End If

        If ModelState.IsValid Then
            If Supplier.SUPPLIER_ID = 0 Then
                objSupplier.CREATED_BY = Session("AppUserID")
                db.SUPPLIER.Add(objSupplier)
            Else
                objSupplier.UPDATED_BY = Session("AppUserID")
                UpdateModel(objSupplier)
            End If

            Try
                db.SaveChanges()
                Return RedirectToAction("Index")
            Catch ex As Exception
                If InStr(ex.InnerException.InnerException.Message, "PRSNL.SUPPLIER_UK") > 0 Then
                    ModelState.AddModelError("SUPPLIER_CODE", "Supplier Code already exists. Please choose another.")
                End If
            End Try

        End If

        'This will run if an error occured
        If Supplier.SUPPLIER_ID > 0 Then
            Supplier = Mapper.Map(Of SupplierViewModel)(objPermStaffAction)
        End If
        ViewBag.YNList = Common.GetYNList
        Return View(Supplier)
    End Function

Answer 1

SupplierViewModel 是引用类型。所以 objPermStaffAction 指的是映射后更新的同一个对象。

为什么需要原始（未映射）对象？