vb.net 从没有 For Each 循环的 DataTable.Select 中获取第一个结果
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Get First result from DataTable.Select without For Each loop
提问by Jegan Nagarajan
The below For loop does not loop at all. Is there any optimized way to do the same without For loop:
下面的 For 循环根本不循环。在没有 For 循环的情况下，是否有任何优化的方法可以做到这一点：
For Each drID As DataRow In dttable.Select("ID=1 and FirstName='Karthik'", "ID")
NewID = CInt(drID.Item("ID"))
Exit For
Next
I have tried changing this with
我试过用
NewID = IIf(dt.Select("ID=1 and FirstName='Karthik'", "ID").Length > 0, dt.Select("ID=1 and FirstName='Karthik'", "ID")(0).Item("ID"), 0)
Is there any other optimized way to change this For loop which does not even loop at all.
有没有其他优化的方法来改变这个根本不循环的 For 循环。
回答by MarcinJuraszek
Looks like you want get "ID"from first row in your DataTable without using For Eachloop. You can do that using LINQ FirstOrDefaultmethod - it returns first element of collection or default value (Nothingfor all reference types) it collection hasn't got results:
看起来您想"ID"在不使用For Each循环的情况下从 DataTable 的第一行获取。您可以使用 LINQFirstOrDefault方法来做到这一点- 它返回集合的第一个元素或默认值（Nothing对于所有引用类型），它的集合没有得到结果：
Dim firstRow As DataRow = dttable.Select("ID=1 and FirstName='Karthik'", "ID").FirstOrDefault()
If Not firstRow Is Nothing Then
NewID = CInt(firstRow.Item("ID"))
Else
NewID = 0
End If
You need Imports System.Linqat the top of your file to make it works.
您需要Imports System.Linq在文件的顶部才能使其正常工作。
Or without LINQ:
或者没有 LINQ：
Dim results As DataRow() = dttable.Select("ID=1 and FirstName='Karthik'", "ID")
If results.Length > 0 Then
NewID = CInt(results(0).Item("ID"))
Else
NewID = 0
End If
