public void VoegBestellingToe(Bestelling bestelling)
        {
            if (bestelling.GeefProducten().Count() != 0)
            {
                SqlConnection connection = getConnection();
                string        query      = "INSERT INTO dbo.bestelling (betaald, prijsBetaald, tijdstip, klantID) OUTPUT INSERTED.bestellingID VALUES (@betaald,@prijsBetaald,@tijdstip,@klantID)";
                string        query2     = "INSERT INTO dbo.bestellingDetails(productID,bestellingID,aantal) VALUES (@productID,@bestellingID,@aantal)";
                using (SqlCommand command1 = connection.CreateCommand())
                    using (SqlCommand command2 = connection.CreateCommand())
                    {
                        connection.Open();
                        SqlTransaction transaction = connection.BeginTransaction();
                        command1.Transaction = transaction;
                        command2.Transaction = transaction;
                        try
                        {
                            //bestelling toevoegen
                            command1.Parameters.Add("@betaald", SqlDbType.Bit).Value        = bestelling.Betaald;
                            command1.Parameters.Add("@prijsBetaald", SqlDbType.Float).Value = bestelling.Kostprijs();
                            command1.Parameters.Add("@tijdstip", SqlDbType.DateTime).Value  = bestelling.Tijdstip;
                            if (bestelling.Klant != null)
                            {
                                command1.Parameters.Add("@klantID", SqlDbType.Int).Value = bestelling.Klant.KlantId;
                            }

                            command1.CommandText = query;
                            int newID = (int)command1.ExecuteScalar();
                            //producten toevoegen
                            command2.Parameters.Add(new SqlParameter("@productID", SqlDbType.Int));
                            command2.Parameters.Add(new SqlParameter("@aantal", SqlDbType.Int));
                            command2.Parameters.Add("@bestellingID", SqlDbType.Int).Value = newID;

                            command2.CommandText = query2;

                            foreach (KeyValuePair <Product, int> kvp in bestelling.GeefProducten())
                            {
                                command2.Parameters["@productID"].Value = kvp.Key.ProductId;
                                command2.Parameters["@aantal"].Value    = kvp.Value;
                                command2.ExecuteNonQuery();
                            }
                            transaction.Commit();
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine(ex);
                        }
                        finally
                        {
                            connection.Close();
                        }
                    }
            }
        }
        public void UpdateBestelling(Bestelling bestelling)
        {
            SqlConnection connection = getConnection();

            string query  = "SELECT * FROM dbo.bestelling b WHERE b.bestellingID = @bestellingID";
            string query2 = "DELETE FROM dbo.bestellingDetails WHERE bestellingID = @bestellingID";
            string query3 = "INSERT INTO dbo.bestellingDetails(productID,bestellingID,aantal) VALUES (@productID,@bestellingID,@aantal)";

            using (SqlDataAdapter adapter = new SqlDataAdapter())
                using (SqlCommand command = connection.CreateCommand())
                {
                    connection.Open();

                    try
                    {
                        //verwijder alles uit bestellingDetails met overeenkomend bestellingID
                        command.Parameters.Add("@bestellingID", SqlDbType.Int).Value = bestelling.BestellingId;
                        command.CommandText = query2;
                        command.ExecuteNonQuery();

                        //voeg nieuwe zaken toe aan bestellingDetails
                        command.Parameters.Add(new SqlParameter("@productID", SqlDbType.Int));
                        command.Parameters.Add(new SqlParameter("@aantal", SqlDbType.Int));
                        command.CommandText = query3;

                        foreach (KeyValuePair <Product, int> kvp in bestelling.GeefProducten())
                        {
                            command.Parameters["@productID"].Value = kvp.Key.ProductId;
                            command.Parameters["@aantal"].Value    = kvp.Value;
                            command.ExecuteNonQuery();
                        }
                        if (bestelling.Betaald)
                        {
                            bestelling.ZetBetaald();
                        }
                        bestelling.Kostprijs();
                        //update bestelling in de database
                        SqlParameter paramId = new SqlParameter();
                        paramId.ParameterName = "@bestellingID";
                        paramId.DbType        = DbType.Int32;
                        paramId.Value         = bestelling.BestellingId;
                        SqlCommandBuilder builder = new SqlCommandBuilder();
                        builder.DataAdapter               = adapter;
                        adapter.SelectCommand             = new SqlCommand();
                        adapter.SelectCommand.CommandText = query;
                        adapter.SelectCommand.Connection  = connection;
                        adapter.SelectCommand.Parameters.Add(paramId);
                        adapter.UpdateCommand = builder.GetUpdateCommand();
                        DataTable table = new DataTable();
                        adapter.Fill(table);
                        table.Rows[0]["betaald"]      = bestelling.Betaald;
                        table.Rows[0]["prijsBetaald"] = bestelling.Kostprijs();
                        table.Rows[0]["tijdstip"]     = bestelling.Tijdstip;
                        table.Rows[0]["klantID"]      = bestelling.Klant.KlantId;

                        adapter.Update(table);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex);
                    }
                    finally
                    {
                        connection.Close();
                    }
                }
        }