Magento 2: How to Prevent item's quantity from being added

Question

Does anybody have clue how to force Magento 2 to not merge into one CartItem the same product on adding to cart?

Let's say I would like to sell ropes and my clients might want to order exactly the same rope but with few different lengths (length is defined by quantity). I would like Magento to add certain products (for example by attribute) always as new CartItem without checking if the same product is actually in cart.

Does anybody struggle with that problem?

Answer 1

To answer you question:

The matching is done by the method Magento\Quote\Model\Quote\Item::representProduct().
This method checks if a certain item in the cart is the same as the product you are just adding to the cart.
Making this method always return false should make any add to cart action add the product as a new line in the cart.

For this you can use an aroundPlugin.

Create a new module and in the etc/di.xml add this

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Quote\Model\Quote\Item">
        <plugin name="[module]-quote-item" type="[Namespace]\[Module]\Plugin\Quote\Item" />
    </type>
</config>

Then create the file [Namespace]/[Module]/Plugin/Quote/Item.php with this content.

<?php
namespace[Namespace]\[Module]\Plugin\Quote;
use Magento\Quote\Model\Quote\Item as QuoteItem;
class Item
{
    public function aroundRepresentProduct(QuoteItem $subject, \Closure $proceed, $product)
    {
        return false;
    }
}

Or a second option could be this. The code is for Magento 1, but you can adapt it for M2. The event recommended in there, sales_quote_add_item, still exists in M2.

To solve your problem, maybe...
If you are planning to sell ropes with fixed lengths maybe you should use configurable products.