How to read and move read content via SQL into variables within VB.net and use a connectionstring from a module in forms? - sql

Question

This is my first question, by the way - and I'm not sure exactly how to ask, or say what's wrong. There's 3 things I can't sort so any help would be appreciated.
Module:
This and the first (login) form work as they are but I couldn't get either Form to reference con.connectionstring for them to use without having to re-use the string contained in "" (as they do below) - my attempts ended up with errors including saying that the state couldn't be changed as the connection was already open, but I'd like the same one string to be referenced from the Forms.
Module ConnectionModule
Public con As OleDb.OleDbConnection = New OleDb.OleDbConnection
Public da As OleDb.OleDbDataAdapter
Public ds As DataSet = New DataSet
Public Path As String = Application.StartupPath
Public Sub OpenDb()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
con.Open()
If con.State = ConnectionState.Closed Then
MsgBox("Connection to db not made.")
End If
End Sub
Public CurrentUser As String = Nothing
End Module
The First Form:
Public Class LoginForm
Private Sub LoginForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
OpenDb()
con.Close()
End Sub
Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
Dim ID As String = txtID.Text
Dim Pass As String = txtPassword.Text
If IsNumeric(ID) = False Or ID.Length > 4 Or Pass = Nothing Then
MsgBox("Staff ID is a 4-digit number and Password must not be blank.")
Else
Dim con As New System.Data.OleDb.OleDbConnection()
OpenDb()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Try
Dim sql As String = "SELECT * FROM tblStaff WHERE [StaffID]='" & ID & "' AND [Pword] = '" & Pass & "'"
Dim sqlCom As New System.Data.OleDb.OleDbCommand(sql)
'Open Database Connection
sqlCom.Connection = con
con.Open()
Dim sqlRead As System.Data.OleDb.OleDbDataReader = sqlCom.ExecuteReader()
If sqlRead.Read() Then 'Correct:
MenuForm.Show()
Me.Hide()
CurrentUser = ID
Else 'Incorrect:
MsgBox("Staff ID or Password incorrect.")
txtPassword.Text = ""
txtID.Text = ""
txtID.Focus()
End If
Catch ex As Exception
MsgBox("Database Connection Error.")
End Try
con.Close()
End If
End Sub
End Class
A form to change the password:
The problem here is that lblUser (A clarification for the user to tell them which password will be changed) only outputs the data already within the program as a variable: CurrentUser (as assigned upon successful login). No error is produced but the full name of the user isn't shown (or possibly read from the database).
I'm also unsure how the UPDATE SQL command should be contained within the second procedure, btnAccept_click, here. What the syntax is, basically. I haven't found a clear example to look at.
Imports System.Data.OleDb
Public Class PasswordForm
Private Sub PasswordForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
con = New System.Data.OleDb.OleDbConnection()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Dim Returned(2) As String
CurrentUser = CurrentUser
Dim cmd As OleDbCommand = New OleDbCommand("SELECT [Title], [Forename], [Surname] FROM tblStaff WHERE [StaffID]='" & CurrentUser & "'", con)
Try
con.Open()
Dim reader As OleDbDataReader = cmd.ExecuteReader()
If reader.HasRows Then
reader.Read()
'Makes db contents variables
Returned(0) = reader.Item("[Title]").ToString
Returned(1) = reader.Item("[Forename]").ToString
Returned(2) = reader.Item("[Surname]").ToString
End If
reader.Close()
Catch ex As Exception
Me.Hide()
MsgBox("Database Connection Error.")
Finally
con.Close()
End Try
lblUser.Text = "Current User: " & CurrentUser & Returned(0) & Returned(1) & Returned(2)
''Only outputs CurrentUser
End Sub
Private Sub btnAccept_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAccept.Click
Dim Current As String = txtCurrent.text
Dim NewPass As String = txtNew.Text
'Verification
If txtNew.Text = txtConfirm.Text And NewPass.Length <= 20 Then
Dim cmd As OleDbCommand = New OleDbCommand("UPDATE tblStaff SET [Pword]='" & NewPass & "' WHERE [StaffID]='" & CurrentUser & "'", con)
End If
End Sub
End Class
Thank you, again, for anyone with ideas (especially exact code).
Oh and throughout what's here there are no errors thrown. Just missing content.

Answer 1

you are opening the connection in openDB() and you are trying to open it again in form1, this will throw the error you are getting. So comment all the con related lines in your form. Same comment for your passowrd form also.
'Dim con As New System.Data.OleDb.OleDbConnection()
OpenDb()
'con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Try
Dim sql As String = "SELECT * FROM tblStaff WHERE [StaffID]='" & ID & "' AND [Pword] = '" & Pass & "'"
Dim sqlCom As New System.Data.OleDb.OleDbCommand(sql)
'Open Database Connection
sqlCom.Connection = con
'con.Open()
...
end try