Change any address field into a selectbox

A customer required me to limit the available towns a customer can order from. So I thought it would be best to make the city field a select option. But Isotope does not seem to offer that option.

I've created a second checkout module with one change from the original. At a certain point inside function generateAddressWidgets, the function checks the field value for the country field. That's where I decided to go hacking and do the following:

Code:

---

                        if ($field['value'] == 'country')
                        {
                                $arrCountries = ($strAddressType == 'billing_address' ? $this->Isotope->Config->billing_countries : $this->Isotope->Config->shipping_countries);

                                $arrData['options'] = array_values(array_intersect($arrData['options'], $arrCountries));
                                $arrData['default'] = $this->Isotope->Config->country;
                        }
                        elseif ($field['value'] == 'city')
                        {
                                $objFields = $this->Database->prepare("SELECT * FROM tl_iso_allowed_places WHERE published = 1")
                                                ->execute();
                                       
                                if ($objFields->numRows)
                                {
                                        unset($arrData['eval']['maxlength']);                               
                                        $strClass = 'FormSelectMenu';
                                        $arrData['inputType'] = 'select';
                                        $arrData['eval']['includeBlankOption'] = true;
                                       
                                        while ($objFields->next())
                                        {
                                                $arrData['options'][htmlspecialchars($objFields->city)] = htmlspecialchars($objFields->city);
                                                $arrData['reference'][htmlspecialchars($objFields->city)] = $objFields->city;
                                        }
                                }
                        }

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This works perfectly so far, but is this a good method to solve this issue. Or does Isotope provide an even better way??