M2.2.4 : Extension attributes of quote models are not properly encoded to the frontend

[kanduvisla]

When I add extension attributes to a quote, they are not properly encoded to the frontend.

Preconditions

1. Magento 2.2.4

Steps to reproduce

1. Create extension attributes for a quote object
2. Populate it with something
3. Check window.checkoutConfig.quoteData.extension_attributes on the checkout page.

For example:

<extension_attributes for="Magento\Quote\Api\Data\CartInterface">
    <attribute code="order_reference_customer" type="string">
        <join reference_table="sales_order_reference" join_on_field="entity_id" reference_field="quote_id">
            <field>customer_reference</field>
        </join>
    </attribute>
</extension_attributes>

In plugin / interceptor for Magento\Quote\Api\CartRepositoryInterface:

/**
 * @param CartRepositoryInterface $subject
 * @param CartInterface $quote
 * @return CartInterface
 */
public function afterGet(CartRepositoryInterface $subject, CartInterface $quote)
{
    $quote->getExtensionAttributes()->setOrderReferenceCustomer('foo');
    return $quote;
}

I've tested if the intercepter worked by good old var_dump and die. The extension attribute is populated and it is present in the quote on the checkout page.

Expected result

window.checkoutConfig.quoteData.extension_attributes should be populated with the extension attributes.

Actual result

Instead it is an empty object {}.

My guesses of what might cause this:

• Magento\Checkout\Model\DefaultConfigProvider::getQuoteData() : Here there is a method called $quote->toArray(), but it does not serialize the extension attributes (these are still objects, and not plain data). or:
• Magento\Checkout\Block\Onepage::getSerializedCheckoutConfig() : This does a simple json_encode() on the data provided by the DefaultConfigProvider. My guess is that it ignores objects.

Possibly related to #15928

[kanduvisla]

For people running into this issue, I wrote a quick fix that can be used in a plugin for Magento\Checkout\Model\DefaultConfigProvider:

/**
 * @param \Magento\Checkout\Model\DefaultConfigProvider $subject
 * @param array $result
 * @return array
 */
public function afterGetConfig(\Magento\Checkout\Model\DefaultConfigProvider $subject, array $result)
{
    /** @var CartExtension $extensionAttributes */
    $extensionAttributes = $result['quoteData']['extension_attributes'] ?? null;

    if ($extensionAttributes instanceof CartExtension) {
        $data = [];
        foreach ($extensionAttributes->__toArray() as $key => $value) {
            if (is_string($value)) {
                $data[$key] = $value;
            }
        }
        $result['quoteData']['extension_attributes'] = $data;
    }

    return $result;
}

The underlying problem I guess, is that even though the __toArray()-method of the extension attributes object serializes it, sometimes it's value is not a string, but an object. In that case, no extension attributes are outputted to the json format.

[engcom-backlog-nickolas]

Hello @kanduvisla, thank you for your report.
We've acknowledged the issue and added to our backlog.

[m2-assistant]

Hi @dani97. Thank you for working on this issue.
Looks like this issue is already verified and confirmed. But if you want to validate it one more time, please, go though the following instruction:

• 1. Add/Edit Component: XXXXX label(s) to the ticket, indicating the components it may be related to.

• 2. Verify that the issue is reproducible on 2.3-develop branch

  Details

  - Add the comment @magento-engcom-team give me 2.3-develop instance to deploy test instance on Magento infrastructure.
  - If the issue is reproducible on 2.3-develop branch, please, add the label Reproduced on 2.3.x.
  - If the issue is not reproducible, add your comment that issue is not reproducible and close the issue and stop verification process here!

• 3. Verify that the issue is reproducible on 2.2-develop branch.

  Details

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  - If the issue is reproducible on 2.2-develop branch, please add the label Reproduced on 2.2.x

• 4. If the issue is not relevant or is not reproducible any more, feel free to close it.