Question

I trust you’re all well. I would like to know what I’m doing wrong and how to fix it. My intent with the code below is the query my MySQL database and display one column of the table inside a ComboBox. Then, when that value in the ComboBox is selected, I want all the records associated to be populated into other controls on my form (I’ll create a separate question for this part).

Right now, the query is working but the ComboBox isn’t being populated. What am I doing wrong? Please help, thanks.

HERE’S MY CODE:

    Private Sub RetrieveMySQLdata()

    Try
        Dim dbConn As New MySqlConnection
        Dim dbQuery As String = ""
        Dim dbCmd As New MySqlCommand
        Dim dbAdapter As New MySqlDataAdapter
        Dim dbTable As New DataTable
        If dbConn.State = ConnectionState.Closed Then
            dbConn.ConnectionString = String.Format("Server={0};Port={1};Uid={2};Password={3};Database=accounting", FormLogin.ComboBoxServerIP.SelectedItem, My.Settings.DB_Port, My.Settings.DB_UserID, My.Settings.DB_Password)
            dbConn.Open()
        End If

        dbQuery = "SELECT *" & _
                   "FROM cc_master INNER JOIN customer ON customer.accountNumber = cc_master.customer_accountNumber " & _
                   "WHERE customer.accountNumber = '" & TextBoxAccount.Text & "'"
        With dbCmd
            .CommandText = dbQuery
            .Connection = dbConn
        End With
        With dbAdapter
            .SelectCommand = dbCmd
            .Fill(dbtable)
        End With
        Dim i As Integer
        For i = 0 To dbTable.Rows.Count - 1
            ComboBoxCard.ValueMember = "ccNumber"

        Next
    Catch ex As Exception
        MessageBox.Show("A DATABASE ERROR HAS OCCURED" & vbCrLf & vbCrLf & ex.Message & vbCrLf & _
                    vbCrLf + "Please report this to the IT/Systems Helpdesk at Ext 131.")
    End Try

End Sub

Answer 1

Where are you trying to populate the ComboBox? The only interaction I see is here:

For i = 0 To dbTable.Rows.Count - 1
    ComboBoxCard.ValueMember = "ccNumber"
Next

Which I’m guessing isn’t doing what you think it’s doing. For one thing, you’re setting ValueMember to the same value multiple times in a loop. Nothing in the statement changes with each iteration of the loop, so why loop it?

More specifically, ValueMember isn’t actually any kind of displayed value. It’s used to indicate which field in the bound data should contain the value. This is used when you provide a DataSource for the control, which you’re missing.

I’ll assume the DataSource should be dbTable, so you’re probably looking to do something like this:

ComboBoxCard.DataSource = dbTable
ComboBoxCard.ValueMember = "ccNumber"
ComboBoxCard.DisplayMember = "Some Other Field in the database"

I don’t remember if you need to explicitly call .DataBind() on the control after these statements, but the example I linked to doesn’t do it so I’ll leave it out.

Essentially what you’re trying to do in your code is loop through the results and add them to the ComboBox. You don’t need to do this. The ComboBox is capable of doing this internally if you just point its DataSource to the set of data being used and tell it which fields it needs to use on that set. This is called data binding.