Magento2 sort products and search result by stock availability

Question

I need to add an option in the Sort By dropdown which sorts the products with based on stock availability of the products.

So far i have created a plugin for setCollection methodMagento\Catalog\Block\Product\ProductList\Toolbar. Check the following code i am using to apply the sort order

public function afterSetCollection($subject)
    {
        $selectedDirection = strtolower($this->_toolbarModel->getDirection());

        if($this->_toolbarBlock->getCurrentOrder() == 'stock'){
            $collection = $subject->getCollection();
            $collection->addAttributeToSort('is_in_stock',$selectedDirection);        
            $collection->getSelect()->joinLeft(
                ['_inventory_table' => 'cataloginventory_stock_item'],
                "_inventory_table.product_id = e.entity_id",
                ['is_in_stock']
            );            
            $collection->getSelect()->order('is_in_stock',$selectedDirection);
            $collection->setOrder('is_in_stock',$selectedDirection);
            /*echo $collection->getSelect();die;*/
        }
        return $subject;
    }

When i print the sql query, it shows the Order By clause applied and if i execute it, it generates correct results, but the product list in the list page does not reflect the same order.

Answer 1

Path : Vendor\ModuleName\etc\di.xml

<?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\Catalog\Model\Layer">
            <plugin name="product_sort_by_stock" type="Company\ModuleName\Model\Plugin\Layer"/>
        </type>
    </config>

Path : Vendor\ModuleName\Model\Plugin\Layer.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Company\ModuleName\Model\Plugin;

/**
 * Catalog view layer model
 *
 * @api
 * @SuppressWarnings(PHPMD.LongVariable)
 * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
 * @since 100.0.2
 */
class Layer
{ 
    /**
     * Retrieve current layer product collection
     *
     * @return \Magento\Catalog\Model\ResourceModel\Product\Collection
     */
    public function aroundgetProductCollection(\Magento\Catalog\Model\Layer $subject, \Closure $proceed)
    {
        $selectedDirection = 'DESC';
        $collection = $proceed(); 
        $collection->getSelect()->order('is_salable '. $selectedDirection);
        return $collection;
    }    
}

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Answer 2

There is no need to use 'around' plugin as only the result should be 'modified'. I'd prefer 'after' plugin instead:

<?php

namespace Company\ModuleName\Plugin;

class Layer
{
    /**
     * @param \Magento\Catalog\Model\Layer $subject
     * @param \Magento\Catalog\Model\ResourceModel\Product\Collection $collection
     * @return \Magento\Catalog\Model\ResourceModel\Product\Collection
     */
    public function afterGetProductCollection(
        \Magento\Catalog\Model\Layer $subject,
        \Magento\Catalog\Model\ResourceModel\Product\Collection $collection
    ) {
        $collection->getSelect()->order('is_salable DESC');
        return $collection;
    }
}

Answer 3

Please update your code to sort according to current direction (By ASC or By DESC)

  $collection = $subject->getCollection();
  $collection->getSelect()->joinLeft(
         ['_inventory_table' => 'cataloginventory_stock_item'], 
         "_inventory_table.product_id = e.entity_id", ['qty']
  );
  $collection->getSelect()->order(['qty ' . $currentDirection]);