MysqlException was unhandled DataReader with this connection must be closed vb.net - mysql

Question

I have encountered this problem:
ERROR: There is already an open DataReader associated with this Connection which must be closed first.
Please have a look on my code:
Dim sqlQuery As String = "SELECT * FROM users"
Dim myAdapter As New MySqlDataAdapter
If txtUsername.Text = String.Empty And txtPassword.Text = String.Empty Then
MsgBox("Enter username and password", MsgBoxStyle.Exclamation, "Tea Sparkle POS")
Else
Dim sqlquerry = "Select * From users where username = '" + txtUsername.Text + "' And password= '" + txtPassword.Text + "'"
Dim myCommand As New MySqlCommand()
myCommand.Connection = SQLConnection
myCommand.CommandText = sqlquerry
'Starting The Query
myAdapter.SelectCommand = myCommand
Dim mydata As MySqlDataReader
mydata = myCommand.ExecuteReader()
'To check the Username and password and to validate the login a
If mydata.HasRows = 0 Then
MsgBox("Invalid Login")
txtPassword.Clear()
txtUsername.Clear()
Else
Dim authorityid = 0
While mydata.Read()
authorityid = mydata.GetInt32("authorityid")
End While
MsgBox("Welcome " + txtUsername.Text + "!")
If authorityid = 1 Then
MainForm.Show()
Else
MainForm.Show()
End If
Me.Hide()
End If
End If
Private Sub Login_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
SQLConnection.ConnectionString = ServerString
Try
If SQLConnection.State = ConnectionState.Closed Then
SQLConnection.Open()
Else
SQLConnection.Close()
End If
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
This error is in this line:
mydata = myCommand.ExecuteReader()
What's wrong with this? Any help is truly appreciated.

Answer 1

What's wrong with this?
Well, it looks like you're reusing an existing connection:
myCommand.Connection = SQLConnection
Don't do that. Create a new connection each time you need to talk to the database, and close it when you've finished, using a Using statement to make sure it gets closed even if an exception is thrown.
Additionally, use a Using statement for your command, and another for your reader - these are all resources you should be closing.
Oh, and it also looks like you're doing this in the UI thread, which is a bad idea as your UI will be unresponsive while the database access is ongoing.