Magento 2: How to add validation for existing address before Order Place

Question

I added one custom field to customer's address & add validation when the customer adds the new address on checkout. And it's working perfectly.

But If I use an old existing address, that field is not there in the address, and the order place successfully.

So I want to add the validation if the field is empty if an existing address is used by the customer.

Answer 1

You can do this via obsever, here is how.

on your etc\events.xml

<event name="checkout_submit_before">
        <observer name="checkout_submit_before" instance="vendor\module\Observer\SubmitOrderBefore" />
    </event>

At Observers folder

<?php
    namespace vendor\module\Observer;
    
    use \Magento\Framework\Event\ObserverInterface;
    use \Magento\Store\Model\StoreManagerInterface;
    use Magento\Framework\App\Response\RedirectInterface;
    
    class SubmitOrderBefore implements ObserverInterface
    {   
        protected $resultRedirectFactory;
        protected $resource;
        
        public function __construct(
            \Magento\Framework\Controller\Result\RedirectFactory $_resultRedirectFactory,
            \Magento\Framework\App\ResourceConnection $_resource
        ) 
        {
            $this->resultRedirectFactory = $_resultRedirectFactory;
            $this->resource              = $_resource;
        }
        
        public function execute(
            \Magento\Framework\Event\Observer $observer
        )
        {
            $quote              = $observer->getEvent()->getQuote();
            $shippingAddress    = $quote->getShippingAddress();
            if(!isset($shippingAddress->getData('your_field_here'))
            {            
                exit;
            }                    
        }
    }
    ?>

This will redirect the client to the cart page when he hits the place order button on the final checkout step.