How to handle empty dataset? - asp.net

Question

I am making Log in page for my project but I am getting an error "There is no row at position 0" while running.
I tried these lines of codes.
Imports System.Data.SqlClient
Imports System.Data
Partial Class Dept_login
Inherits System.Web.UI.Page
Protected Sub BtnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles BtnSubmit.Click
Dim ds As New DataSet
'Try
Dim con As New SqlConnection(ConfigurationManager.ConnectionStrings("VMSConnectionString").ConnectionString)
con.Open()
Dim cmd As New SqlCommand("SELECT password FROM Dept_login WHERE user_id='" + Txtuname.Text + "'", con)
Dim da As New SqlDataAdapter(cmd)
da.Fill(ds)
If Not IsDBNull(ds) Then
If Txtpwd.Text = ds.Tables(0).Rows(0).Item("password") Then
Response.Redirect("Online Services.aspx") 'the page i want to redirect to after login successful
Else
Label1.Visible = True 'initially visible is false and text is INVALID PASSWORD
End If
con.Close()
' Catch ex As Exception
' End Try
End If
End Sub
Private Function Dept_login() As Integer
Throw New NotImplementedException
End Function
End Class

Answer 1

This line doesn't make sense:
If Not IsDBNull(ds) Then
ds will never be DBNull. Instead, check for the number of rows coming back, like:
If ds.Tables(0).Rows.Length > 0 Then
You're trying to get the first row (.Rows(0)) when there aren't any - that's what the error is telling you.
Try using something like this:
If ds.Tables(0).Rows.Count > 0 AndAlso Txtpwd.Text = ds.Tables(0).Rows(0).Item("password") Then
Response.Redirect("Online Services.aspx", False) 'the page i want to redirect to after login successful
Context.ApplicationInstance.CompleteRequest();
Else
Label1.Visible = True 'initially visible is false and text is INVALID PASSWORD
End If
con.Close()
' Catch ex As Exception
' End Try
(Note: You should use parameterization for the SQL query. You're leaving yourself open to a SQL injection attack.)

Answer 2

This line doesn't make sense:
If Not IsDBNull(ds) Then
Makes sense
If ds.Tables(0).Rows.count > 0 andalso ds.Tables..count > 0 Then
END IF
Hope this helps

Answer 3

Did you try using a datareader instead of a dataadapter?
Try
Dim datare As SqlDataReader
Using cn As New SqlConnection(ConfigurationManager.ConnectionStrings("VMSConnectionString").ConnectionString)
Using cmd As New SqlCommand("SELECT password FROM Dept_login WHERE user_id='#User'", cn)
cmd.Parameters.AddWithValue("#User", Txtuname.Text)
cn.Open()
datare = cmd.ExecuteReader()
With datare
If .Read() Then
If .Item(0) = txtpwd.Text Then
Response.Redirect("Online Services.aspx")
Else
Label1.Visible = True
End If
End If
End With
End Using
End Using
Catch ex As Exception
Throw ex
End Try
Also, on the query you write user_id. did you mean username? Is you query correct?