Fatal error encountered during command execution.' - vb.net

Question

I want to save the rows of datagridview into the database. I am using editbtn click button, when I press the button it gives me the following error: "Fatal error encountered during command execution." Here is the code which I am using
Private Sub Supplier_Load(sender As Object, e As EventArgs) Handles MyBase.Load
conn.ConnectionString = "Server=127.0.0.1;Database=pembelian;Uid=root;Pwd=;"
If conn.State = ConnectionState.Open Then
conn.Close()
End If
conn.Open()
disp_data()
End Sub
Public Sub disp_data()
cmd = conn.CreateCommand()
cmd.CommandType = CommandType.Text
cmd.CommandText = "select * from supplier"
cmd.ExecuteNonQuery()
Dim dt As New DataTable()
Dim da As New MySqlDataAdapter(cmd)
da.Fill(dt)
DataGridView1.DataSource = dt
End Sub
Private Sub edit_btn_Click(sender As Object, e As EventArgs) Handles edit_btn.Click
Dim query As String = "updates supplier set nama=#nama, alamat=#alamat where npwp=#npwp"
cmd = New MySqlCommand(query, conn)
cmd.Parameters.AddWithValue("#nama", nama.Text)
cmd.Parameters.AddWithValue("#alamat", alamat.Text)
cmd.ExecuteNonQuery()
MessageBox.Show("Data berhasil di update")
disp_data()
End Sub

Answer 1

First of all, it's not good to re-use the same connection object throughout your application. There is a feature in ADO.Net called connection pooling, where the MySqlConnection object you use in your code is actually a simple wrapper for the real underlying connection. These real connections are much heavier and more expensive to manage. They handle the real work of authentication, getting network socket resources, negotiating with the server, etc.
When you try to re-use the same connection object, you are optimizing the small thing (MySqlConnection) at the expense of the big thing (the real underlying connections). Don't do that.
Instead, you really are much better off creating a new connection for most queries, and then returning it to the pool as quickly as possible. This is normally handled with a Using block.
That out of the way I can look at the actual question. I noticed the #npwp parameter is not defined in the last method. Guessing at the name of the appropriate field, you want something more like this:
Private Sub edit_btn_Click(sender As Object, e As EventArgs) Handles edit_btn.Click
Dim query As String = "updates supplier set nama=#nama, alamat=#alamat where npwp=#npwp"
Using conn As New MySqlConnection("Server=127.0.0.1;Database=pembelian;Uid=root;Pwd=;")
Using cmd As New MySqlCommand(query, conn)
cmd.Parameters.AddWithValue("#nama", nama.Text)
cmd.Parameters.AddWithValue("#alamat", alamat.Text)
cmd.Parameters.AddWithValue("#npwp", npwp.Text)
conn.Open()
cmd.ExecuteNonQuery()
End Using
End Using
MessageBox.Show("Data berhasil di update")
disp_data()
End Sub
Public Sub disp_data()
Dim dt As New DataTable()
Dim query As String = "select * from supplier"
Using conn As New MySqlConnection("Server=127.0.0.1;Database=pembelian;Uid=root;Pwd=;")
Using cmd As New MySqlCommand(query, conn)
Using da As New MySqlDataAdapater(cmd)
da.Fill(dt)
End Using
End Using
End Using
DataGridView1.DataSource = dt
End Sub