Question

I’m starting to put in a database into my application, however I’m drawing a blank on how to share a database connection among the dozen or so different forms in my MDI application. I’m assuming this has to do with interfaces or something but I can’t find any relevant examples anywhere. Can someone help me out? Ideally what I’d like is when the app is loaded up there is a call to a function in the forms loading area which establishes a single connection to the mdb, that I can then call via any form so I don’t always have to open/close connections everytime I need to update the db (assuming what I’m suggesting is better for overhead), unless that is a better option?

Here’s a basic example of the mdb database access code I’ve got working:

    Dim dt As DataTable = New DataTable()
    Dim OleDbTran As OleDbTransaction = Nothing

    Using connJET As OleDbConnection = New OleDbConnection("connection string here...")
        Try
            connJET.Open()
            Dim sqlCount As OleDbCommand = New OleDbCommand("select * from mytable", connJET)
            Using aReader As OleDbDataReader = sqlCount.ExecuteReader()
                dt.Load(aReader)
            End Using

            If (dt.Rows.Count > 0) Then
                MsgBox(dt.Rows.Count)
            End If

            OleDbTran = connJET.BeginTransaction()
            Dim aCommand As OleDbCommand = connJET.CreateCommand()
            aCommand.CommandText = "INSERT INTO Programs (title) VALUES (@title)"
            aCommand.Transaction = OleDbTran

            aCommand.Parameters.Add("@title", OleDbType.VarChar)
            aCommand.Parameters("@title").Value = "Test"

            aCommand.ExecuteNonQuery()
            OleDbTran.Commit()
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Using

Answer 1

Assuming that you create the connection in your startup form, then you could just add constructors to the other forms that accept a SqlConnection and send that in whenever you create an instance of that form.

Or if you prefer, you create something like this:

Public Class Connection
    Private Shared connection As OleDb.OleDbConnection

    Public Shared ReadOnly Property Instance As OleDb.OleDbConnection
        Get
            If connection Is Nothing Then
                connection = New OleDb.OleDbConnection("connstring")
            End If
            Return connection
        End Get
    End Property
End Class

And then you could access it by just calling Connection.Instance whenever you need it.