How to Modify Discount amount of cart price rule on cart page in magento 2

Question

I would like to modify Discount Amount of cart price rule on the cart page. Actually Magento apply rule using class Magento\SalesRule\Model\RulesApplier and function is protected function setDiscountData($discountData, $item)

So for that, I create a preference to modify Discount Amount

<preference for="Magento\SalesRule\Model\RulesApplier" type="Namespace\Modulename\Model\RulesApplier" />

And my logic like below :

<?php
namespace Namespace\Modulename\Model;

use Namespace\Modulename\Model\Source\ShowCoupon;
use Magento\SalesRule\Model\Quote\ChildrenValidationLocator;
use Magento\SalesRule\Model\Rule\Action\Discount\CalculatorFactory;
use Namespace\Modulename\Model\Source\PromotionType;

class RulesApplier extends \Magento\SalesRule\Model\RulesApplier
{
    /**
     * @var \Magento\SalesRule\Model\ResourceModel\Rule\Collection
     */
    protected $rules;

    /**
     * @var \Magento\SalesRule\Model\Utility
     */
    protected $validatorUtility;

    public function __construct(
        CalculatorFactory $calculatorFactory,
        \Magento\Framework\Event\ManagerInterface $eventManager,
        \Magento\SalesRule\Model\Utility $utility,
        \Magento\SalesRule\Model\ResourceModel\Rule\CollectionFactory $rulesFactory,
        ChildrenValidationLocator $childrenValidationLocator = null
    ){
        $this->ruleCollection = $rulesFactory;
        parent::__construct($calculatorFactory, $eventManager, $utility, $childrenValidationLocator);
    }

    protected function setDiscountData($discountData, $item)
    {
        $item->setDiscountAmount(0);
        $item->setBaseDiscountAmount(0);
        $item->setOriginalDiscountAmount(0);
        $item->setBaseOriginalDiscountAmount(0);

        $quote = $item->getQuote();
        $quote->setCustomAmount($discountData->getAmount());
        $quote->setBaseCustomAmount($discountData->getBaseAmount());
        //echo '<pre>';print_r($quote->debug());die;
        return $this;
    }
}

In the above code, I am trying to set discount amount to zero and I want to set that discount amount to my custom fee value. but unfortunately, it is not working.

So I debug that and found that if you set $item->setDiscountAmount(0); to zero then the value is not set to your custom fee. so can someone help me to solve out this issue? what's I am doing wrong or is there any other method available?

In short, I would like to set discount amount to may custom fee and default discount amount($item->setDiscountAmount(0)) to zero at the same time same file

Any help would be appreciated! Thanks.

Answer 1

You can set the discount amount as below :

1.Create a sales.xml file in [vendor-name]/[module-name]/etc/sales.xml with

 <?xml version="1.0"?>
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Sales:etc/sales.xsd">
    <section name="quote">
      <group name="totals">
        <item name="[custom-name]" instance="[vendor-name]\[module-name]\Model\Total\CartUpdate" sort_order="500"/>
      </group>  
    </section>
 </config> 

2.Create a file CartUpdate.php in [vendor-name]/[module-name]/model/Total with

  <?php
  namespace [vendor-name]\[module-name]\Model\Total;

  class CartUpdate extends \Magento\Quote\Model\Quote\Address\Total\AbstractTotal
  {
      protected $priceCurrency;

      public function __construct(
      \Magento\Framework\Pricing\PriceCurrencyInterface $priceCurrency
     )
     {
          $this->priceCurrency = $priceCurrency;
     }

     public function collect(
        \Magento\Quote\Model\Quote $quote,
        \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment,
        \Magento\Quote\Model\Quote\Address\Total $total
     ) 
     {
         parent::collect($quote, $shippingAssignment, $total);     

         $customDiscount = 10;
         $discount =  $this->priceCurrency->convert($customDiscount);
         $total->setTotalAmount('discount', -$discount);
         $total->setBaseTotalAmount('discount', -$customDiscount);
         $total->setBaseGrandTotal($total->getBaseGrandTotal() - $customDiscount);
         $quote->setDiscount(-$discount);
         return $this;
      } 
 }

The result will be:

Here I set the discount amount as 10.You can set discount amount as 0 or above. If you want to set a discount as 0 then it will not be shown in frontend.

Hope this will be help you.....