Magento 2.1.x search by relevance does not work EE CE

Please see my answer on the same GitHub post

https://github.com/magento/magento2/issues/9066

In a custom module, I utilised plugin (which uses Interceptor Design Pattern) for getCurrentOrder method in `Magento\Catalog\Block\Product\ProductList\Toolbar`.

For this example, I would use an arbitrary module named `Namesapce_Modulename`. So, once the module is created, in `etc/frontend/di.xml` use the following code:

<?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\Block\Product\ProductList\Toolbar">
   <plugin name="namespace_modulename_catalog_product_list_toolbar_after_get_current_order"
           type="Namespace\Modulename\Plugin\Catalog\Block\Product\ProductList\Toolbar"
           sortOrder="1"
           disabled="false"
   />
</type>
</config>

Now inside the plugin class

`Namespace/Modulename/Plugin/Catalog/Block/Product/ProductList/Toolbar.php`
use the following code:

<?php

namespace Namespace\Modulename\Plugin\Catalog\Block\Product\ProductList;

use Magento\Catalog\Model\Product\ProductList\Toolbar as ToolbarModel;
use Magento\Catalog\Model\Session as CatalogSession;
use Namespace\Modulename\Helper\Data as Helper;

class Toolbar extends \Magento\Framework\View\Element\Template
{
    protected $toolbarModel;

    protected $paramsMemorizeAllowed = true;

    protected $catalogSession;

    protected $helper;


    public function __construct(
        ToolbarModel $toolbar,
        CatalogSession $catalogSession,
        Helper $helper
    ) {
        $this->toolbarModel = $toolbar;
        $this->catalogSession = $catalogSession;
        $this->helper = $helper;
    }

    public function afterGetCurrentOrder(
        \Magento\Catalog\Block\Product\ProductList\Toolbar $subject
    ) {
        if (!$this->helper->getSearchSortOrderByRelevance()) {
            return;
        }

        $order = $subject->_getData('_current_grid_order');
        $orders = $subject->getAvailableOrders();
        $toolbarOrder = $this->toolbarModel->getOrder();

        if ($order && !isset($orders['relevance'])) {
            return $order;
        } else if ($order
            && isset($orders['relevance'])
            && $toolbarOrder == null
        ) {
            $keys = array_keys($orders);
            $defaultOrder = $keys[2];
        } else {
            $keys = array_keys($orders);
            $defaultOrder = $keys[0];
        }

        if (!$order || !isset($orders[$toolbarOrder])) {
            $order = $defaultOrder;
        }

        if ($order != $defaultOrder) {
            $this->memorizeParam('sort_order', $order);
        }

        $subject->setData('_current_grid_order', $order);

        return $order;
    }

    protected function memorizeParam($param, $value)
    {
        if ($this->paramsMemorizeAllowed && !$this->catalogSession->getParamsMemorizeDisabled()) {
            $this->catalogSession->setData($param, $value);
        }
        return $this;
    }

}

I also created a “Yes/No” admin configuration setting to make sure when Magento core team implement the fix this plugin can be disabled without touching any code. And using a helper return method getSearchSortOrderByRelevance, I am checking if we need to set the search result order to relevance.

Hope this helps someone.

Cheers!