int InvoiceID = 11;

using (var db = new InvoicingDBContainer())
{
    //materialize an invoice
    //this will produce a SELECT statement
    var invoice = db.Invoice
        .Include("InvoiceElement") //eager-load elements for deletion
        .FirstOrDefault(x => x.InvoiceID == InvoiceID);

    //manually load elements for deletion
    //no lazy-load works for cascade delete objects
    //db.Entry(invoice).Collection("InvoiceElement").Load();

    //informs EF context to remove invoice from database
    db.Invoice.Remove(invoice);

    //asks EF context to persist changed entities
    //this will produce the DELETE statement
    db.SaveChanges();
}