What's the best way to parse an SQL fragment string into a List(of string) for a Listbox control? - asp.net

Question

I'm trying to take this string:
(("DISPLAY_NAME" like N'sadf%') And ("ID" = 2) And ("IsCRITERION" = null))
and parse it into a List(of string) so that it can be displayed like:
(
(
"DISPLAY_NAME" like N'sadf%'
)
And
(
"ID" = 2
)
Or
(
"IsCRITERION" = null
)
)
I'm close but don't quite have it. My code currently looks like:
Dim filterlist As New List(Of String)
Dim temp As String = String.Empty
Dim lvl As Integer = 0
Dim pad As String = String.Empty
For Each chr As Char In originalString '--- filter is the string i posted above
Select Case chr.ToString.ToLower()
Case "("
filterlist.Add(pad.PadLeft(lvl * 5) & chr)
lvl += 1
Case ")"
filterlist.Add(pad.PadLeft(lvl * 5) & temp)
If lvl > 0 Then lvl -= 1
filterlist.Add(pad.PadLeft(lvl * 5) & chr)
'If lvl > 0 Then lvl -= 1
temp = String.Empty
Case Else
temp &= chr
End Select
Next
'--- Removes the empty line produced by generating the List(of String)
filterlist = filterlist.Where(Function(s) Not String.IsNullOrWhiteSpace(s)).ToList()
listSelectedCriteria.DataSource = filterlist
listSelectedCriteria.DataBind()
Unfortunately, the above code produces something close to what I desire but the "And"s and "Or"s are not in the right places:
(
(
"DISPLAY_NAME" like N'sadf%'
)
(
And "ID" = 2
)
(
Or "IsCRITERION" = null
)
)
Would using regular expressions be better? Thanks for the help

Answer 1

Probably the "best" way (although that's getting into "primarily opinion-based" territory) would be to use a parser, but assuming that your input is limited to similar looking strings, here's what I came up with:
Dim originalString = "((""DISPLAY_NAME"" like N'sadf%') And (""ID"" = 2) And (""IsCRITERION"" = null))"
Dim filterlist = New List(Of String)()
Dim temp = New StringBuilder()
Dim lvl = 0
Dim addLine =
Sub(x As String)
filterlist.Add(New String(" ", lvl * 4) & x.Trim())
End Sub
For Each c In originalString
Select Case c
Case "("
If temp.Length > 0 Then
addLine(temp.ToString())
temp.Clear()
End If
addLine("(")
lvl += 1
Case ")"
If temp.Length > 0 Then
addLine(temp.ToString())
temp.Clear()
End If
lvl -= 1
addLine(")")
Case Else
temp.Append(c)
End Select
Next
If temp.Length > 0 Then
addLine(temp.ToString())
temp.Clear()
End If
filterlist.Dump() ' LINQPad ONLY
This results in:
(
(
"DISPLAY_NAME" like N'sadf%'
)
And
(
"ID" = 2
)
And
(
"IsCRITERION" = null
)
)
However, you will probably end up having to add code as you find different inputs that don't quite work how you want.

Answer 2

Instead of looking at each characters, I would start be doing a split. And then add/remove padding depending on what character is at the start.
Dim tempString As String = "((""DISPLAY_NAME"" like N'sadf%') And (""ID"" = 2) And (""IsCRITERION"" = null))"
Dim curPadding As String = ""
Const padding As String = " "
Dim result As New List(Of String)
For Each s As String In Text.RegularExpressions.Regex.Split(tempString, "(?=[\(\)])")
If s <> "" Then
If s.StartsWith("(") Then
result.Add(curPadding & "(")
curPadding &= padding
result.Add(curPadding & s.Substring(1).Trim())
ElseIf s.StartsWith(")") Then
curPadding = curPadding.Substring(padding.Length)
result.Add(curPadding & ")")
result.Add(curPadding & s.Substring(1).Trim())
Else
result.Add(curPadding & s)
End If
End If
Next