Magento 2 copy extension attribute value from quote to order

Question

I have an extension attribute on quote address called "subdistrict". The data is successfuly saved to quote_address. But when completing the order, these data are not saved to sales_order_address.

below is my fieldset.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:DataObject/etc/fieldset.xsd">
<scope id="global">
    <fieldset id="sales_convert_quote_address">
        <field name="subdistrict">
            <aspect name="to_order_address" />
        </field>
    </fieldset>
</scope>

and my extensions_attributes.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
<extension_attributes for="Magento\Quote\Api\Data\AddressInterface">
    <attribute code="subdistrict" type="string" />
</extension_attributes>
<extension_attributes for="Magento\Sales\Api\Data\OrderAddressInterface">
    <attribute code="subdistrict" type="string" />
</extension_attributes>

right now i am getting an error:

"Error occurred during "shipping_address" processing. Error occurred during "extension_attributes" processing. Error occurred during "subdistrict" processing. Invalid type for value: "array". Expected Type: "string"."

and here is some part of the quote content:

  ["city"]=>
  string(14) "Kab. Tangerang"
  ["firstname"]=>
  string(7) "Yohanes"
  ["lastname"]=>
  string(7) "Pradono"
  ["customAttributes"]=>
  array(1) {
    ["subdistrict"]=>
    array(2) {
      ["attribute_code"]=>
      string(11) "subdistrict"
      ["value"]=>
      string(8) "Balaraja"
    }
  }
  ["extension_attributes"]=>
  array(1) {
    ["subdistrict"]=>
    array(2) {
      ["attribute_code"]=>
      string(11) "subdistrict"
      ["value"]=>
      string(8) "Balaraja"
    }
  }
  ["same_as_billing"]=>

and my mixin.js

define([
    'jquery',
    'mage/utils/wrapper',
    'Magento_Checkout/js/model/quote'
], function ($, wrapper, quote) {
    'use strict';

    return function (setShippingInformationAction) {

        return wrapper.wrap(setShippingInformationAction, function (originalAction) {
            var shippingAddress = quote.shippingAddress();
            if (shippingAddress['extension_attributes'] === undefined) {
                shippingAddress['extension_attributes'] = {};
            }

            // you can extract value of extension attribute from any place (in this example I use custom_attributes approach)
            // Don: the actual data to be sent to Magento backend is inside 'extension_attributes'
            console.log(shippingAddress);
            shippingAddress['extension_attributes']['subdistrict'] = shippingAddress.customAttributes['subdistrict'];
            // pass execution to original action ('Magento_Checkout/js/action/set-shipping-information')
            return originalAction();
        });
    };
});

Answer 1

I finally be able to convert the subdistrict to order address. Aparantly, some tutorials out there put wrong information on the mixin js content. it should be likethis

    if (shippingAddress.customAttributes != undefined) {
        $.each(shippingAddress.customAttributes , function( key, value ) {

            if($.isPlainObject(value)){
                value = value['value'];
            }

            shippingAddress['customAttributes'][key] = value;
            shippingAddress['extension_attributes'][key] = value;

        });
    }

And I also have to manually convert quote address subdistrict to order address using Observer on event sales_model_service_quote_submit_before

    public function execute(\Magento\Framework\Event\Observer $observer)
{
    // copy shipping address subdistrict
    $quoteShippingAdress = $observer->getQuote()->getShippingAddress();
    $subdistrict = $quoteShippingAdress->getSubdistrict();
    $orderShippingAdress = $observer->getOrder()->getShippingAddress();
    $orderShippingAdress->setSubdistrict($subdistrict);

    // copy billing address subdistrict
    $quoteBillingAddress = $observer->getQuote()->getBillingAddress();
    $subdistrict = $quoteBillingAddress->getSubdistrict();
    $orderBillingAddress = $observer->getOrder()->getBillingAddress();
    $orderBillingAddress->setSubdistrict($subdistrict);

}

as additional info, Magento 2.1 fieldset.xml doesn't support extension_attributes fields so they have to be converted manually.