DbCart.php

<?php
//plugin
use Illuminate\Support\Facades\Event;

use Commerce\Carts\ProductsCart;
use Commerce\Carts\SessionCartStore;
use Commerce\Currency;
use EvolutionCMS\Facades\AuthServices as Auth;
use EvolutionCMS\Main\Controllers\Shop\DbCartClass;

Event::listen(['evolution.OnInitializeCommerce'], function ($params) {
	ci()->commerce->currency = new Currency(evo());
	$carts = ci()->carts;

	$carts->registerStore('session', SessionCartStore::class);
	$carts->registerStore('custom_db', DbCartClass::class);

	$cartSession = new ProductsCart(evo(),'session_products_instance','session');
	$cartDb = new ProductsCart(evo(), 'db_products_instance', 'custom_db');
	$carts->addCart('session_products_instance', $cartSession);
	$carts->addCart('db_products_instance', $cartDb);
});


Event::listen(['evolution.OnUserLogout'], function ($params) {

});

DbCartClass.php

<?php

namespace EvolutionCMS\Main\Controllers\Shop;
use EvolutionCMS\Facades\AuthServices as Auth;
use Commerce\Interfaces\CartStore;

/**
 * store cart to db
 */
class DbCartClass implements CartStore
{
    protected $modx;
    protected $instance = '';
    protected $id = 0;
    protected $cartKey = '';
    protected $items = [];
    protected $uid;

    public function __construct()
    {
        $this->modx = ci()->modx;
        $this->uid =  (int) $this->modx->getLoginUserID('web') ? (int) $this->modx->getLoginUserID('web') : null;
    }

    public function load($instance = 'cart')
    {
        $this->instance = $instance;
        return $this->loadCart();
    }

    public function save(array $items)
    {
        if (!$this->id && !empty($items)) {
            $this->createCart();
        };
        $old = array_keys($this->items);
        $new = array_keys($items);
        $delete = array_diff($old, $new);
        if (!empty($delete)) {
            $rows = \APIhelpers::sanitarIn($delete);
            $this->modx->db->query("DELETE FROM {$this->modx->getFullTableName('commerce_db_cart_products')} WHERE `cart_id` = {$this->id} AND `row` IN ({$rows})");
        }
        $insert = array_diff($new, $old);
        $update = array_intersect($new, $old);
        foreach ($update as $row) {
            if ($items[$row] != $this->items[$row]) {
                $insert[] = $row;
            }
        }
        foreach ($insert as $row) {
            $item = $items[$row];
            $data = [
                'cart_id'    => $this->id,
                'product_id' => (int) $item['id'],
                'hash'       => $item['hash'],
                'row'        => $row,
                'title'      => $this->modx->db->escape(trim(isset($item['title']) ? $item['title'] : $item['name'])),
                'price'      => $this->normalizeFloat($item['price']),
                'count'      => $this->normalizeFloat($item['count']),
                'options'    => json_encode(isset($item['options']) && is_array($item['options']) ? $item['options'] : [], JSON_UNESCAPED_UNICODE),
                'meta'       => json_encode(isset($item['meta']) && is_array($item['meta']) ? $item['meta'] : [], JSON_UNESCAPED_UNICODE),
            ];
            $fields = '`' . implode('`,`', array_keys($data)) . '`';
            $values = \APIhelpers::sanitarIn(array_values($data));
            $this->modx->db->query("INSERT IGNORE INTO {$this->modx->getFullTableName('commerce_db_cart_products')} ({$fields}) VALUES ({$values}) ON DUPLICATE KEY UPDATE `product_id` = {$data['product_id']}, `count` = '{$data['count']}', `title` = '{$data['title']}', `price` = '{$data['price']}', `options` = '{$data['options']}', `meta` = '{$data['meta']}'");
        }

        $this->items = $items;
        if (!empty($delete) || !empty($insert)) {
            $this->updateCart();
        }
    }


    /**
     * @params id, hash
     */
    protected function loadCart()
    {
        $items = [];
        $instance = $this->modx->db->escape($this->instance);

        if(!$this->uid){
            return false;
        }
        $q = $this->modx->db->query("SELECT `id` FROM {$this->modx->getFullTableName('commerce_db_carts')} WHERE `customer_id`= {$this->uid} AND `instance` = '{$instance}'");
        if ($id = $this->modx->db->getValue($q)) {
            $this->id = $id;
            $q = $this->modx->db->query("SELECT * FROM {$this->modx->getFullTableName('commerce_db_cart_products')} WHERE `cart_id` = {$id} ORDER BY `id` ASC");
            while ($row = $this->modx->db->getRow($q)) {
                $items[$row['row']] = [
                    'id'      => $row['product_id'],
                    'name'    => $row['title'],
                    'price'   => $row['price'],
                    'count'   => $row['count'],
                    'hash'    => $row['hash'],
                    'row'     => $row['row'],
                    'options' => \jsonHelper::jsonDecode($row['options'], ['assoc' => true], true),
                    'meta'    => \jsonHelper::jsonDecode($row['meta'], ['assoc' => true], true),
                ];
            }
        } else {
            $this->id = 0;
            //?
            //$this->createCart();
        }
        $this->items = $items;
        return $items;
    }

    protected function createCart( )
    {



        $hash = ci()->commerce->generateRandomString(32);
        $instance = $this->modx->db->escape($this->instance);
        $updated_at = date('Y-m-d H:i:s', time() + $this->modx->getConfig('server_offset_time'));
        $q = $this->modx->db->query("INSERT INTO {$this->modx->getFullTableName('commerce_db_carts')} (`instance`, `hash`, `customer_id`, `updated_at`) VALUES ('{$instance}', '{$hash}', {$this->uid}, '{$updated_at}')");
        $this->id = $this->modx->db->getInsertId();
    }

    protected function updateCart()
    {
        $id = $this->id;
        $updated_at = date('Y-m-d H:i:s', time() + $this->modx->getConfig('server_offset_time'));
        $update = [];
        $update[] = "`updated_at` = '{$updated_at}'";
        $update[] = "`updated_at` = '{$this->uid}'";
        $update = implode(',', $update);
        $this->modx->db->query("UPDATE {$this->modx->getFullTableName('commerce_db_carts')} SET {$update} WHERE `id` = {$id}");
    }

    protected function normalizeFloat($value)
    {
        $value = str_replace(',', '.', $value);
        return number_format((float) $value, 6, '.', '');
    }

}

OnUserLogin.php

<?php

use Illuminate\Support\Facades\Event;

Event::listen(['evolution.OnUserLogin'], function ($params)   {
	if(evo()->isBackend()) return;
	if(!function_exists('ci')){evo()->invokeEvent('OnWebPageInit');}
	$carts = ci()->carts;
	$sessionCart = ci()->carts->getCart('session_products_instance');	// корзина анонима
	$sessionItems = $sessionCart->getItems();							//	товары анонима
	$dbCart = ci()->carts->getCart('db_products_instance');				//	корзина юзера в БД
	$dbItems = $dbCart->getItems();										//	товары юзера

	if( count($sessionItems) === 0){
		//	корзина анонима пуста, берём товар из корзины в БД
		//	В плагине DbCart мы сменим инстанс, товары
		//	будут из корзины БД. И делать ничего не надо
		
	}else{
		
		//	корзина анонима не пуста, нужно объединить её и корзину в БД

		if(count($dbItems) === 0){
			//	в корзине БД пусто, в сессии не пусто
			//	надо удалить из сессии и добавить в БД корзину
			foreach ($sessionItems as $key => $item) {
				$dbCart->add($item, false);
			}
		}
		else{
			//	в обоих корзинах что-то есть
			//	нужно сливать товары
			
			foreach ($sessionItems as $key => $sessionItem) {
				foreach ($dbItems as $k => $dbItem) {
					if($dbItem['id'] != $sessionItem['id'] && $dbItem['hash'] != $sessionItem['hash']){
						$dbCart->add($sessionItem,  false);
					}
				}
				
			}			
		}
		//	почистить корзину сессии 
		//	она нам больше не нужна, товары на месте
		$sessionCart->clean();
	}
});