Add value for custom quote item attribute using REST api

Question

I want to add value for custom quote attribute using rest api. This attribute is not a product attribute. I have created a database column in quote_item table. Also created the plugin on class Magento\Quote\Model\Quote\Item\Repository on method save().

I am using the extension_attributes to get the value for custom attribute. Below is my request body.

{ "cartItem": 
    { 
        "quote_id": "70", 
        "sku": "VNLIC", 
        "qty": 1,  
        "extension_attributes": {
            "custom_message" : "Quote Item Custom Message Text"
        }   
    } 
}

The plugin code is below:

<?php

namespace Vendor\ModuleName\Plugin;

class QuoteItemRepository
{
    public function beforeSave(
        \Magento\Quote\Model\Quote\Item\Repository\Interceptor $subject,
        $cartItem
    )
    {
        $extensionAttr = $cartItem->getExtensionAttributes();
        if($extensionAttr !== null) {

            $customMessage = $extensionAttr->getCustomMessage();
            if($customMessage !== null) {
                $cartItem->setData('custom_message', $customMessage);
            }

            //$cartItem->save();
        }
        return [$cartItem];
    }
}

If I use this there is no value get populated in the quote_item table for the custom_message column.

If I uncomment $cartItem->save() then I am getting the below error.

Fatal error: Uncaught Error: Call to a member function setFinalPrice() on null in /var/www/html/bakeway/vendor/magento/module-quote/Model/Quote/Item/AbstractItem.php on line 152

Please help.

Answer 1

1.Try to use the around save method in the plugin file.

public function aroundSave(
       CartItemRepositoryInterface $subject, \Closure $proceed, CartItemInterface $entity
 ): mixed
{ }

2.After setting the custom attribute and trying to use the resource model file for saving the attribute.

3.Class Resource File for Quote Item Magento\Quote\Model\ResourceModel\Quote\Item

4.$this->resourceModel->save($cartItem);

Give thump up if it's work.