ASP.Net/VB.Net/LINQ：无法将 .objectquery 类型的对象转换为 generic.list 类型

Question

我有一个关于 ASP.Net、visual basic 的问题 我有 2 个 LINQ 查询，第一个有效，第二个无效，产生一个

"Unable to cast object of type 'System.Data.Objects.ObjectQuery'1[SelmaV2.Products]' to type 'System.Collections.Generic.List'1[System.String]'.

代码如下：

Sub GetProducts(ByRef productDropList As DropDownList)
    Dim productList As New List(Of String)
    Using context As New SelmaEntities
        productList = (From products In context.Products
                       Order By products.Product
                       Select products.Product).Distinct.ToList()
    End Using
    productDropList.DataSource = productList
End Sub
Sub GetProductNames(ByRef ProductNamesList As List(Of String), ByVal CurrentProduct As String)
    Using context As New SelmaEntities
        ProductNamesList = (From products In context.Products
                            Where products.Product = CurrentProduct
                            Order By products.Product_no Ascending
                            Select products).ToList
    End Using
End Sub

Answer 1

您正在尝试获取字符串 列表，但看起来您正在选择产品 列表。我怀疑你想要类似的东西

Select products.Product

而不是

Select products

在查询中。 （您的命名也有点不幸，因为products 一次仍然只引用一个产品 - 我个人会将那个范围变量重命名为product。）