how to search and update record mysql in vb - mysql

Question

i have problem to search and update record database sql.
this is my code. i using mysql database and Microsoft Visual Basic 2008
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim t As New Threading.Thread(AddressOf closeMsgbox)
objconn = New MySqlConnection("server=localhost;database=AAA;userid=root;password= 'root'")
Dim username As Boolean = True
objconn.Open()
Dim sqlquery As String = "SELECT * FROM daftar WHERE nid = '" & FormRegister.TextBox1.Text & "';"
Dim data As MySqlDataReader
Dim adapter As New MySqlDataAdapter
Dim command As New MySqlCommand
command.CommandText = sqlquery
command.Connection = objconn
adapter.SelectCommand = command
data = command.ExecuteReader
If data.HasRows() = True Then
While data.Read()
FormRegister.Show()
tkhupd = Now.ToString("yyyy-MM-dd HH:mm:ss")
command.Connection = objconn
command.CommandText = "UPDATE visitor SET tkhupd ='" & tkhupd & "' WHERE nokp = '" & FormRegister.TextBox1.Text & "';"
command.ExecuteNonQuery()
MessageBox.Show("You're has logout")
FormRegister.TextBox1.Text = ""
username = False
Me.Close()
End While
Else
FormRegister.Show()
username = True
End If
data.Close()
If username = True Then
Dim sqlquery2 As String = "INSERT INTO visitor (nid)VALUES ('" & FormRegister.TextBox1.Text & "')"
Dim data2 As MySqlDataReader
Dim adapter2 As New MySqlDataAdapter
Dim command2 As New MySqlCommand
command2.CommandText = sqlquery2
command2.Connection = objconn
adapter2.SelectCommand = command2
data2 = command2.ExecuteReader
MessageBox.Show("You're has login")
Form4.Show()
FormRegister.TextBox1.Text = ""
Me.Close()
End If
End Sub
but i have error on Word command.ExecuteNonQuery(): MySqlException was unhandled. There is already an open DataReader associated with this Connection which must be closed first

Answer 1

You need to use a separate MySqlCommand object, say command2 inside your While statement , because command is already in active use:
Dim command2 As New MySqlCommand
..
While data.Read()
..
command2.Connection = objconn
..
End While

Answer 2

I would do this all in one call to the database, comprising two statements. I'm more used to Sql Server, so this syntax may be a little off, but it would look something like this:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim sqlquery As String = _
"DECLARE #RowCount Int;" & _
" UPDATE FROM visitor v" & _
" INNER JOIN daftar d ON d.nid = v.nokp" & _
" SET v.tkhupd = current_timestamp" & _
" WHERE d.nid = ?NID;" & _
" SELECT row_count() INTO #RowCount;" & _
" IF #RowCount = 0 THEN " & vbCrLf & _
" INSERT INTO visitor (nid) VALUES (?NID);" & vbCrLf & _
" END IF"
Using conn As New MySqlConnection("server=localhost;database=AAA;userid=root;password= 'root'"), _
cmd As New MySqlCommand(sqlquery, conn)
cmd.Parameters.Add("?NID", MySqlDbTypes.Int).Value = Integer.Parse(FormRegister.TextBox1.Text)
conn.Open()
cmd.ExecuteNonQuery()
End Using
End Sub