protected function getInvoiceLinesFields()
    {
        $fields = array(
            'itemNumber' => array(
                'type' => 'text',
                'label' => $this->t('field_itemNumber'),
                'description' => $this->t('desc_itemNumber') . ' ' . $this->t('msg_token'),
                'attributes' => array(
                    'size' => 60,
                ),
            ),
            'productName' => array(
                'type' => 'text',
                'label' => $this->t('field_productName'),
                'description' => $this->t('desc_productName') . ' ' . $this->t('msg_token'),
                'attributes' => array(
                    'size' => 60,
                ),
            ),
            'nature' => array(
                'type' => 'text',
                'label' => $this->t('field_nature'),
                'description' => $this->t('desc_nature'),
                'attributes' => array(
                    'size' => 30,
                ),
            ),
            'costPrice' => array(
                'type' => 'text',
                'label' => $this->t('field_costPrice'),
                'description' => $this->t('desc_costPrice') . ' ' . $this->t('msg_token'),
                'attributes' => array(
                    'size' => 60,
                ),
            ),
        );
        return $fields;
    }