InvalidCastException when retrieving data from SqlDataReader - sql

Question

How can I get rid of:
System.InvalidCastException: 'Conversion from string "Type" to type
'Integer' is not valid.'"
On the line:
Dim usertype = Reader.GetString("Type")
This is my full code:
Private Sub OKbt1_Click(sender As Object, e As EventArgs) Handles OKbt1.Click
Call Connect() ' [ connection to module ]'
Dim Reader As SqlDataReader
Try
Dim command As New SqlCommand("select * from uinfo where password = '" & PASStb2.Text & "'", sqlConn)
Reader = command.ExecuteReader
Reader.Read()
Dim count As Integer = 0
While Reader.Read
count = count + 1
End While
If count = 1 Then
' ** MY ERROR **
Dim usertype = Reader.GetString("Type")
If usertype = "admin" Then
'MsgBox("username and password are correct")
MAIN_MENU.Show()
For a = 0 To 500
Next
Me.Hide()
sqlConn.Close()
sqlConn.Dispose()
ElseIf usertype = "user" Then
For a = 0 To 500
Next
Me.Hide()
'MsgBox("username and password are correct")
USERMENU.Show()
End If
ElseIf count > 1 Then
MsgBox("username and password are duplicate")
Else
MsgBox("username and password are not correct")
End If
sqlConn.Close()
Catch ex As SqlException
MsgBox(ex.Message)
Finally
sqlConn.Dispose()
End Try
End Sub

Answer 1

SqlDataReader.GetString Method (Int32) needs an integer (column index) as a parameter. So you need
Dim usertype as String = Cstr(Reader("Type"))
or
Dim usertype = Reader.GetString(Reader.GetOrdinal("Type"))
or
Dim usertype = Reader.GetFieldValue(Of String)("Type")
Be aware that non of those posibilites can handle DBnull.

Answer 2

'Reader.GetString' accepts an integer parameter, not a string. Or, do
Reader.Item("Type").ToString()

Answer 3

Declare usertype as Dim usertype as String and then assign value to it like usertype = Reader.Item("Type").ToString().
also you need to check value return by Reader.GetString("Type") it might be null. Turn "Option Strict" On It will help in the long run.

Answer 4

**Dim usertype = Reader.GetString("Type") // MY ERROR**
You are passing a value of string which obviously is wrong
GetString function accepts integer.
You might want to instantiate a data which is integer and pass it through getstring.
Dim usertype = Reader.GetString(data)

Answer 5

Use parameters. I let the server do the counting. Saves you some lines of code.
Private Sub OKbt1_Click(sender As Object, e As EventArgs) Handles OKbt1.Click
Call Connect() ' [ connection to module ]'
Dim Reader As SqlDataReader
Try
Using cmd As New SqlCommand("select usertype, Count(*) from uinfo Group By usertype where [password] = #password;", sqlConn)
cmd.Parameters.Add("#password", SqlDbType.VarChar).Value = PASStb2.Text
Reader = cmd.ExecuteReader()
If Reader.HasRows Then
Reader.Read()
Dim usertype As String = Reader.GetString(0)
Dim count As Integer = Reader.GetInt32(1)
If count = 1 Then
If usertype = "admin" Then
MAIN_MENU.Show()
Hide()
ElseIf usertype = "user" Then
USERMENU.Show()
Hide()
End If
ElseIf count > 1 Then
MsgBox("username and password are duplicate")
End If
Else
MsgBox("username and password are not correct")
End If
End Using
Catch ex As Exception
MsgBox(ex.Message)
Finally
sqlConn.Close()
sqlConn.Dispose()
End Try
End Sub

Answer 6

It is because you may not getting data from "Reader" object properly
Try this instead :
Dim command As SqlCommand = New SqlCommand("SELECT * FROM uinfo WHERE password = '" & PASStb2.Text & "'", connection)
connection.Open()
Dim READER As SqlDataReader = command.ExecuteReader()
If READER.HasRows Then
While READER.Read()
Console.WriteLine("{0}" & vbTab & "{1}", READER.GetInt32(0), READER.GetString(1))
End While
Else
Console.WriteLine("No rows found.")
End If
READER.Close()