Parent Child Combobox using a database in visual basic

[Milosz Laksa]

Hello I am struggling to get some code working for my project. I am quite new to vb.net and database programming so I don't quite know how to get it to work. The code I am trying to do is in this link https://www.vbforums.com/showthread.php?518065 but using a database. I need the user input to the parent combo box to then change the data in the child Combo box. Here is what I got so far if anyone could point me in the right direction? I also get this error message

System.ArgumentNullException: ''column' argument cannot be null. Parameter name: column'

 Dim data As DataSet = Me.GetDataSet()


    Me.BindingSource1.DataSource = data
    Me.BindingSource1.DataMember = "RoomType"

    Me.BindingSource2.DataSource = Me.BindingSource1
    Me.BindingSource2.DataMember = "Rooms"

    Me.cmbRoomType.DisplayMember = "roomtype.RoomTypeName"
    Me.cmbRoomType.ValueMember = "roomtype.RoomTypeID"
    Me.cmbRoomType.DataSource = Me.BindingSource1

    Me.cmbRoomNumber.DisplayMember = "roomsRoomNumber"
    Me.cmbRoomNumber.ValueMember = "rooms.RoomID"
    Me.cmbRoomNumber.DataSource = Me.BindingSource2



End Sub
Private ConStr As String = "Data Source=dbNEAProject.db"

Private Function GetDataSet() As DataSet
    Dim data As New DataSet
    Dim parent As DataTable = Me.GetRoomType()
    Dim child As DataTable = Me.GetRoomNumber()


    data.Tables.Add(parent)
    data.Tables.Add(child)
    data.Relations.Add("Rooms",
                           parent.Columns("roomtype.RoomTypeID"),
                           child.Columns("Rooms.rRoomTypeID"))
    Return data
End Function
Private Function GetRoomType() As DataTable
    Dim sql As String = "Select RoomTypeName, RoomTypeID FROM RoomType"
    Dim table As New DataTable("RoomType")
    Using con As New SQLiteConnection(ConStr)
        con.Open()
        Using da As New SQLiteDataAdapter(sql, con)
            da.Fill(table)

        End Using
    End Using
    Return table
End Function

Private Function GetRoomNumber() As DataTable
    Dim sql As String = "Select RoomNumber, RoomID, rRoomTypeID FROM Rooms INNER JOIN roomtype ON roomtype.roomtypeid = rooms.rroomtypeid ;"
    Dim table As New DataTable("RoomNumber")
    Using con As New SQLiteConnection(ConStr)
        con.Open()
        Using da As New SQLiteDataAdapter(sql, con)
            da.Fill(table)
        End Using
    End Using
    Return table
End Function