magento2/app/code/Magento/SalesGraphQl/Model/Resolver/ProductResolver.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

namespace Magento\SalesGraphQl\Model\Resolver;

use Magento\Catalog\Model\Product;
use Magento\CatalogGraphQl\Model\ProductDataProvider;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\GraphQl\Config\Element\Field;
use Magento\Framework\GraphQl\Query\ResolverInterface;
use Magento\Framework\GraphQl\Schema\Type\ResolveInfo;

/**
 * Fetches the Product data according to the GraphQL schema
 */
class ProductResolver implements ResolverInterface
{
    /**
     * @var ProductDataProvider
     */
    private $productDataProvider;

    /**
     * @param ProductDataProvider $productDataProvider
     */
    public function __construct(ProductDataProvider $productDataProvider)
    {
        $this->productDataProvider = $productDataProvider;
    }

    /**
     * @inheritdoc
     */
    public function resolve(
        Field $field,
        $context,
        ResolveInfo $info,
        array $value = null,
        array $args = null
    ) {
        if (!isset($value['associatedProduct'])) {
            throw new LocalizedException(__('Missing key "associatedProduct" in Order Item value data'));
        }
        /** @var Product $product */
        $product = $value['associatedProduct'];

        return $this->productDataProvider->getProductDataById((int) $product->getId());
    }
}