Requested entity doesn\'t exist in Magento 2

I had the same error showing on Admin > Sales > Orders when trying to access a list of all orders.

It turned out to be a discrepancy between two tables sales_order and sales_order_grid. Some records in sales_order_grid didn't have corresponding records in sales_order table. Luckily, it was my dev environment so I could easily remove offending records. So if you get this error (Requested entity doesn't exist) it's most likely a data integrity issue.

\Magento\Sales\Api\OrderRepositoryInterface::get receive order id, not increment_id. Use getList, if you need to search order by increment_id

/**
 * @param OrderRepositoryInterface $orderRepository
 * @param SearchCriteriaBuilder $searchCriteriaBuilder
 */
public function __construct(
    OrderRepositoryInterface $orderRepository,
    SearchCriteriaBuilder $searchCriteriaBuilder
) {
    $this->orderRepository = $orderRepository;
    $this->searchCriteriaBuilder = $searchCriteriaBuilder;
}

/**
 * Get order by increment id.
 *
 * @param string $incrementId
 * @return OrderInterface
 * @throws NoSuchEntityException
 */
public function getOrderByIncrementId($incrementId)
{
    $searchCriteria = $this->searchCriteriaBuilder->addFilter(
        OrderInterface::INCREMENT_ID,
        $incrementId
    )->create();

    $result = $this->orderRepository->getList($searchCriteria);

    if (empty($result->getItems())) {
        throw new NoSuchEntityException(__('No such order.'));
    }

    $orders = $result->getItems();

    return reset($orders);
}