Question

我有两个LINQ查询，按过滤器顺序不同。我想避免使用嵌套的Sub CopyRange() Dim bottomD As Integer Dim ws As Worksheet For Each ws In Sheets(Array("A", "B", "C", "D")) ws.Activate bottomD = Range("E" & rows.Count).End(xlUp).Row Range("E2:G" & bottomD).Copy Sheets("Summary").Cells(rows.Count,"E").End(xlUp).Offset(1, 0) Next ws Dim r As Range Dim rows2 As Long Dim i As Long Set r = ActiveSheet.Range("A:A") rows2 = r.rows.Count For i = rows2 To 1 Step (-1) If WorksheetFunction.CountA(r.rows(i)) = 0 Then r.rows(i).Delete Next End Sub语句。

我目前的方法是：

If

Answer 1

我更喜欢在LINQ查询的Select Case或Sort部分使用OrderBy语句，因为它更容易阅读：

Select Case search.Sort
    Case "Name"
        OutputList = OutputList.OrderBy(Function(x) x.Name).ToList()

    Case "-Name"
        OutputList = OutputList.OrderByDescending(Function(x) x.Name).ToList()

    Case "Date"
        OutputList = OutputList.OrderBy(Function(x) x.[Date]).ToList()

    Case "-Date"
        OutputList = OutputList.OrderByDescending(Function(x) x.[Date]).ToList()

    Case "Percent"
        OutputList = OutputList.OrderBy(Function(x) x.CompletedPercentage).ToList()

    Case "-Percent"
        OutputList = OutputList.OrderByDescending(Function(x) x.CompletedPercentage).ToList()

End Select

Answer 2

如果我理解正确你只想避免嵌套if语句。您可以通过使用函数实现此操作，并在条件有效时将函数保留为Return。

Function GetUserNames(userList As List(Of UserList), username As String)
    If (userList Is Nothing OrElse Not userList.Any()) Then
        Return New List(Of String)
    End If

    If Filter() Then
        Return From u In userList Order By (If(u.Name = username, 1, 0)) Descending, u.Name Ascending
    End If

    Return From u In userList
           Select u.Name Distinct
           Order By Name Descending
End Function

请注意，您没有嵌套if语句，实际上您也不需要其他部分。

还可以通过构建语句来利用linq。假设应该为两个查询应用Distinct名称：

    Dim query = userList.Select(Function(u) u.Name).Distinct

    If Filter() Then
        Return query.OrderByDescending(Function(n) If(n = username, 1, 0)).ThenBy(Function(n) n)
    End If

    Return query.OrderBy(Function(n) n)

- 更新 -

赏金要求提供可信和/或官方来源的答案。＆＃39;。这就是为什么我包含了Martin Fowler文章的链接，其中描述了这种设计：

https://www.refactoring.com/catalog/replaceNestedConditionalWithGuardClauses.html

Answer 3

假设我正确解释了您的代码，为什么不删除所有的If语句？

    Dim sortUsername = If(Filter(), "", username)
    users = (From u In userlist Order By If(u.name > sortUsername, 1, 0) Descending, u.name Ascending Select u.name Distinct).ToList

Answer 4

您可以在LINQ中使用let关键字，并拥有一个将用于制定决策的变量。

如何使用LINQ过滤对象列表而不使用嵌套的If语句

4 个答案: