Can not retrieve data from MySql database - vb.net

Question

when I run the code, I have an error message that says: Object reference not set to an instance of an object. I would like to create a code that verify credentials that are in the database. If the user that not enter valid information, an error message appears. Here is my code:
'Declare variables
Dim pwd, username As String
Dim dbpwd, dbUsername As String
'Get credentials variables
username = Me.username.Text
pwd = Me.TextBox2.Text
Dim objConn As MySqlConnection
Dim objDataset As New DataSet
Dim objDataAdapter As MySqlDataAdapter
Dim sqlConn As String
If username <> "" And pwd <> "" Then
objConn = New MySqlConnection("server=localhost;userid=root;password= ;database=mayombe_mdcs")
objConn.Open()
sqlConn = "select agent_id, Password from password where agent_id = " & username & ""
Try
objDataAdapter = New MySqlDataAdapter(sqlConn, objConn)
objDataAdapter.Fill(objDataset)
' intRowNumber = sqlR
dbUsername = objDataset.Tables("password").Rows(1).Item(2)
' dbpwd = objDataset.Tables("password").Rows(1).Item(1)
'WriteLine (dbUsername )
'Force users to enter credentiasl
objConn.Close()
'Force user to enter true credentials
If pwd = dbpwd And username = dbUsername Then
open form
Me.Close()
End If
Catch ex As Exception
strMsg As String
Prompt message that tells the user that credentials entered are not correct.
strMsg = String.Format("One of the following is incorrect: {0}* Username entered {0}* Password entered.", Environment.NewLine)
MessageBox.Show(strMsg, "Warning")
End Try

Answer 1

There are some things wrong in your code.
First, if agent_id is a varchar field you need to use single quotes around the value used in the where clause, but it is better to avoid this problem and use a parameterized query.
Second, if you find something then you should refer to the first row using index 0 and to the second column using index 1. Your code assumes that indexing of an array starts at index 1 but this is not true in the NET world. Arrays always start at index 0.
I would try to rewrite your code as this
objDataset = new Dataset()
sqlConn = "select agent_id, Password from password where agent_id = #usr"
using objConn = New MySqlConnection(....)
objConn.Open()
Try
objDataAdapter = New MySqlDataAdapter(sqlConn, objConn)
objDataAdapter.SelectCommand.Parameters.AddWithValue("#usr", username)
objDataAdapter.Fill(objDataset)
if objDataset.Tables(0).Rows.Count > 0 Then
dbUsername = objDataset.Tables(0).Rows(0).Item(1).ToString
End If
End Using