Question

This is so simple, I must be stupid!

I have a simple access database that a log record gets written to a few times an hour.

I’m trying to make a DataGridView that shows that data as it arrives.

My “Solution” is simple;

when a user clicks the view -> read from the database (fill the datatable) -> update the view.

Not what I dreamed of, but functional, if totally sub-optimal.

However, my “solution” is a dud, using fill draws every single record from the database, even if there are already 599 on screen.

Really, I just want fill the datatable once, and add new records as they arrive (or on click if needs be).

Bonus point if you can also explain another way (that isn’t called so often) to hide the ID column, and change the header of column 1 (named DateTimeStamp) to TimeStamp.

Public Class FormMain

    Shared dataAdapter As OleDbDataAdapter
    Shared logTable As New DataTable("log")
    Shared commandBuilder As OleDbCommandBuilder
    Shared queryString As String = "SELECT * FROM log"
    Shared bindingSource As New BindingSource

    Private Sub FormServerBridge_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Try
            ConfigureDataSet()
            ConfigureBindingSource()
            ConfigureDataView()
        Catch ex As Exception
            ' FIXME: Helpful for debugging purposes but awful for the end-user.
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    Private Sub ConfigureDataSet()
        dataAdapter = New OleDbDataAdapter(queryString, _Config.ConnectionString)
        commandBuilder = New OleDbCommandBuilder(dataAdapter)
        commandBuilder.GetUpdateCommand()

        dataAdapter.Fill(logTable)

        With logTable
            .Locale = System.Globalization.CultureInfo.InvariantCulture
            .PrimaryKey = New DataColumn() {logTable.Columns("ID")}
        End With
    End Sub

    Private Sub ConfigureBindingSource()
        With bindingSource
            .DataSource = logTable
        End With
    End Sub

    Private Sub ConfigureDataView()
        With DataGridView
            .DataSource = bindingSource
        End With
    End Sub

    Private Sub DataGridView_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView.Click
        UpdateUI()
    End Sub

    Sub UpdateUI()
        dataAdapter.Fill(logTable)
    End Sub

    Private Sub DataGridView_DataBindingComplete(ByVal sender As Object, ByVal e As DataGridViewBindingCompleteEventArgs) Handles DataGridView.DataBindingComplete

        ' FIXME: This code gets run as many times as there are rows after dataAdapter.Fill!

        With DataGridView
            .Columns("ID").Visible = False

            .Columns(1).HeaderText = "Timestamp"

            .Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.AllCells
            .Columns(2).AutoSizeMode = DataGridViewAutoSizeColumnMode.AllCells
            .Columns(3).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
        End With

    End Sub
End Class

p.s. Links to websites and books will be appreciated, even the right MSDN page (if you know where it is, I admit I find it uncomfortable to peruse, I regularly get lost).

Answer 1

Assuming your IDs are sequential, the way I would approach this is:

1) Record the last id that you retrieved

2) When the user presses view, only get records whose IDs are greater than the last one record

3) Retrieve the records into a new datatable and then merge that with your existing data set.

Here is how I would make the changes (only changed info included):

Public Class FormMain

    Shared logTable As DataTable
    Shared bindingSource As New BindingSource

    Private m_wLastID As Integer

    Private Sub FormServerBridge_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Try
            ConfigureDataSet()
            ConfigureBindingSource()
            ConfigureDataView()
        Catch ex As Exception
            ' FIXME: Helpful for debugging purposes but awful for the end-user.
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    Private Sub ConfigureDataSet()

        Dim queryString As String

        queryString = "SELECT * FROM log WHERE ID > " & m_wLastID.ToString & " ORDER BY ID"

        Using dataAdapter As New OleDbDataAdapter(queryString, _Config.ConnectionString)
            Using commandBuilder As New OleDbCommandBuilder(dataAdapter)
                Dim oDataTable As New DataTable("log")

                commandBuilder.GetUpdateCommand()

                dataAdapter.Fill(oDataTable)

                With oDataTable
                    .Locale = System.Globalization.CultureInfo.InvariantCulture
                    .PrimaryKey = New DataColumn() {.Columns("ID")}
                End With

                ' Record the last id
                If oDataTable.Rows.Count <> 0 Then
                    m_wLastID = CInt(oDataTable.Rows(oDataTable.Rows.Count - 1)("ID"))
                End If

                If logTable Is Nothing Then
                    logTable = oDataTable
                Else
                    logTable.Merge(oDataTable, True)
                    logTable.AcceptChanges()
                End If
            End Using
        End Using
    End Sub

    Sub UpdateUI()
        ConfigureDataSet()
    End Sub

    ' Rest of the form code here