VB.NET LINQ按“选择新建”分组不能访问类成员BC30456

问题描述

我正在尝试从以下教程中将一些C＃代码转换为VB.NET，该教程显示了如何使用LINQ Group By Into生成带有行组标题的HTML表：

https://ole.michelsen.dk/blog/grouping-data-with-linq-and-mvc/

C＃代码按宣传的方式工作，但是我的VB.NET转换有问题。

我在VB.NET中遇到问题的C＃代码行：

// Group the books by Genre
var booksGrouped = from b in books
                   group b by b.Genre into g
                   select new Group<string,Book> { Key = g.Key,Values = g };

Visual Studio报告的“ g.Key”为：

string IGrouping<string,Book>.Key

在VB.NET中，两个类Group和Book看起来像这样：

Public Class Group(Of K,T)
    Public Property Key As K
    Public Property Values As IEnumerable(Of T)
End Class

Public Class Book
    Public Title As String
    Public Author As String
    Public Genre As String
    Public Price As Decimal
End Class

上面的C＃代码行作为VB.NET：

Dim booksGrouped = From b In books Group b By b.Genre Into g = Group
                   Select New Group(Of String,Book) With {.Key = g.Key,.Values = g}

注意：我必须在“ Into”子句中添加“ = Group”，否则“ g”会出现错误“ BC36594：在这种情况下无法访问方法'g'的定义。”

Visual Studio报告“ g.Key”现在是IEnumerable：

BC30456: 'Key' is not a member of 'IEnumerable(of Book)'.

因此C＃正在看到IGroup接口，而VB.NET正在看到IEnumerable。

我喜欢本教程中提供的解决方案的简单性，并且真的很想在VB.NET中实现它，是否有人对如何使它起作用有任何想法？

非常感谢。

VB.NET中的示例数据是

Dim books As New List(Of Book)

books.Add(New Book With {.Author = "Douglas Adams",.Title = "The Hitchhiker's Guide to the galaxy",.Genre = "Fiction",.Price = 159.95D})
books.Add(New Book With {.Author = "Scott Adams",.Title = "The Dilbert Principle",.Price = 23.95D})
books.Add(New Book With {.Author = "Douglas Coupland",.Title = "Generation X",.Price = 300D})
books.Add(New Book With {.Author = "Walter Isaacson",.Title = "Steve Jobs",.Genre = "Biography",.Price = 219.25D})
books.Add(New Book With {.Author = "Michael Freeman",.Title = "The Photographer's Eye",.Genre = "Photography",.Price = 195.5D})

解决方法

您需要声明谁将成为您的钥匙。根据您的代码，假设为Genre。因此，您需要按照Morton的建议使用分组功能，或者必须为分组的List(of Book)

确定“键”

下面的代码显示了如何：

    Dim booksGrouped = From b In books
                       Group b By Key = b.Genre Into g = Group
                       Select New Group(Of String,Book) With {.Key = Key,.Values = g}


    For Each current In booksGrouped
        For Each value In current.Values
            With value
                Console.WriteLine("Key:" & current.Key & "value: " & Strings.Join({ .Genre,.Author,.Price,.Title}," - "))
            End With
        Next
    Next

,

您不需要明确说明密钥-C＃代码指定了“ g.Key”，但是C＃正在确定它必须为“流派”：

Dim booksGrouped = From b In books
    Group b By b.Genre Into g = Group
    Select New Group(Of String,Book) With {
        .Key = Genre,.Values = g
    }