Custom sort by is not working with elastic search in magento 2.3

Question

After upgrading magento 2.3 and enabling magento new feature elastic search 6, My custom module for sort by is not working. It is perfectly fine working with MySql option but not working with elastic search.

Below is my custom module code:

CS/SortBy/Plugin/Product/ProductList/Toolbar.php

<?php
namespace CS\SortBy\Plugin\Product\ProductList;

class Toolbar
{
    /**
    * Plugin
    *
    * @param \Magento\Catalog\Block\Product\ProductList\Toolbar $subject
    * @param \Closure $proceed
    * @param \Magento\Framework\Data\Collection $collection
    * @return \Magento\Catalog\Block\Product\ProductList\Toolbar
    */
    public function aroundSetCollection(
        \Magento\Catalog\Block\Product\ProductList\Toolbar $toolbar,
        \Closure $proceed,
        $collection
    ) {
        $this->_collection = $collection;
        $currentOrder = $toolbar->getCurrentOrder();
        $currentDirection = $toolbar->getCurrentDirection();
        $result = $proceed($collection);

        if ($currentOrder) {
            switch ($currentOrder) {

            case 'newest':
                $this->_collection
                    ->getSelect()
                    ->order('e.created_at DESC');
            break;

            case 'price_desc':
                $this->_collection
                    ->getSelect()
                    ->order('price_index.min_price DESC');
            break;

            case 'price_asc':
                $this->_collection
                    ->getSelect()
                    ->order('price_index.min_price ASC');
            break;

            default:        
                $this->_collection
                    ->setOrder($currentOrder, $currentDirection);
            break;

            }
        }
        return $result;
    }
}

CS/SortBy/Plugin/Model/Config.php

<?php
namespace CS\SortBy\Plugin\Model;

class Config
{
    /**
     * Adding custom options and changing labels
     *
     * @param \Magento\Catalog\Model\Config $catalogConfig
     * @param [] $options
     * @return []
     */
    public function afterGetAttributeUsedForSortByArray(\Magento\Catalog\Model\Config $catalogConfig, $options)
    {
        //Remove default sorting options
        unset($options['name']);
        unset($options['price']);

        //New sorting options
        $options['position'] = __('Recommended');
        $options['price_desc'] = __('Price High');
        $options['price_asc'] = __('Price Low');
        $options['newest'] = __('Newest First');

        return $options;
    }
}

Answer 1

you need to change used_for_sort_by to 1 for attribute 'created_at'.

Use setup/patch script to update the attribute value

$prodEntityTypeId = $installer->getEntityTypeId('catalog_product');
$installer->updateAttribute($prodEntityTypeId, 'created_at', 'used_for_sort_by', 1);

# optional if you want the value to come in frontend as Date
$installer->updateAttribute($prodEntityTypeId, 'created_at', 'frontend_label', 'Date');

use the below code to change the created_at functionality https://magento.stackexchange.com/a/149656/27183

Answer 2

Custom Sort with ElasticSearch in Magento issue can be fixed by following these simple steps:

• Navigate to Stores->Attributes->Product in Admin.
• Add New Attribute.
• In Properties->Attribute Properties:
  • Add Default Label (Eg: Price: Low to High)
  • Select the Catalog Input Type for Store Owner (Eg: Price) (In other cases Text Field is enough).
• In Properties->Advanced Attribute Properties:
  • Add Attribute Code (Eg: price_asc).
• In Storefront Properties->Storefront Properties:
  • Select User for Sorting in Product Listing to Yes

Once done with the above steps run the following commands,

bin/magento indexer:reindex catalogsearch_fulltext

bin/magento indexer:reindex