Magento 2 – Add New Custom Option Text Field

Here is how I added Inventory text field for Drop-down custom option.

Create a module using following code -

app/code/MyCompany/MyModule/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="MyCompany_MyModule" setup_version="1.0.0" />
</config>

app/code/MyCompany/MyModule/etc/adminhtml/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\CustomOptions" type="MyCompany\MyModule\Ui\DataProvider\Product\Form\Modifier\CustomOptions" />
</config>

app/code/MyCompany/MyModule/Ui/DataProvider/Product/Form/Modifier/CustomOptions.php

<?php
/**
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace MyCompany\MyModule\Ui\DataProvider\Product\Form\Modifier;


use Magento\Catalog\Model\Locator\LocatorInterface;
use Magento\Store\Model\StoreManagerInterface;
use Magento\Catalog\Model\ProductOptions\ConfigInterface;
use Magento\Catalog\Model\Config\Source\Product\Options\Price as ProductOptionsPrice;
use Magento\Framework\UrlInterface;
use Magento\Framework\Stdlib\ArrayManager;
use Magento\Ui\Component\Modal;
use Magento\Ui\Component\Container;
use Magento\Ui\Component\DynamicRows;
use Magento\Ui\Component\Form\Fieldset;
use Magento\Ui\Component\Form\Field;
use Magento\Ui\Component\Form\Element\Input;
use Magento\Ui\Component\Form\Element\Select;
use Magento\Ui\Component\Form\Element\Checkbox;
use Magento\Ui\Component\Form\Element\ActionDelete;
use Magento\Ui\Component\Form\Element\DataType\Text;
use Magento\Ui\Component\Form\Element\DataType\Number;
use Magento\Framework\Locale\CurrencyInterface;


class CustomOptions extends \Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\CustomOptions
{
    /**#@+
     * Field values
     * 
     */
    const FIELD_QTY_NAME = 'quantity';

    /**
     * Get config for grid for "select" types
     * 
     * @param int $sortOrder
     * @return array
     */
    protected function getSelectTypeGridConfig($sortOrder)
    {
        return [
            'arguments' => [
                'data' => [
                    'config' => [
                        'addButtonLabel' => __('Add Value'),
                        'componentType' => DynamicRows::NAME,
                        'component' => 'Magento_Ui/js/dynamic-rows/dynamic-rows',
                        'additionalClasses' => 'admin__field-wide',
                        'deleteProperty' => static::FIELD_IS_DELETE,
                        'deleteValue' => '1',
                        'renderDefaultRecord' => false,
                        'sortOrder' => $sortOrder,
                    ],
                ],
            ],
            'children' => [
                'record' => [
                    'arguments' => [
                        'data' => [
                            'config' => [
                                'componentType' => Container::NAME,
                                'component' => 'Magento_Ui/js/dynamic-rows/record',
                                'positionProvider' => static::FIELD_SORT_ORDER_NAME,
                                'isTemplate' => true,
                                'is_collection' => true,
                            ],
                        ],
                    ],
                    'children' => [
                        static::FIELD_TITLE_NAME => $this->getTitleFieldConfig(10),
                        static::FIELD_PRICE_NAME => $this->getPriceFieldConfig(20),
                        static::FIELD_PRICE_TYPE_NAME => $this->getPriceTypeFieldConfig(30, ['fit' => true]),
                        static::FIELD_SKU_NAME => $this->getSkuFieldConfig(40),
                        static::FIELD_SORT_ORDER_NAME => $this->getPositionFieldConfig(50),
                        static::FIELD_QTY_NAME => $this->getQtyFieldConfig(55),
                        static::FIELD_IS_DELETE => $this->getIsDeleteFieldConfig(60)
                    ]
                ]
            ]
        ];
    }

    /**
     * Get config for "Inventory" fields
     * 
     * @param $sortOrder 
     * @param array $options
     * @return array
     */
    protected function getQtyFieldConfig($sortOrder, array $options = [])
    {
        return array_replace_recursive(
            [
                'arguments' => [
                    'data' => [
                        'config' => [
                            'label' => __('Inventory'),
                            'componentType' => Field::NAME,
                            'formElement' => Input::NAME,
                            'dataScope' => static::FIELD_QTY_NAME,
                            'dataType' => Text::NAME,
                            'sortOrder' => $sortOrder,
                            'validation' => [
                                'validate-digits' => true
                            ],
                        ],
                    ],
                ],
            ],
            $options
        );
    }
}

Add a column with name 'quantity' in Database table 'catalog_product_option_type_value' for storing the inventory value.

Hope this helps.

Create a plugin for that. So you need to create new module Or add following code into your existing module.

SR/StackExchange/etc/adminhtml/di.xml

<?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\Model\Config\Source\Product\Options\Price">
        <plugin name="sr_stackexchange_add_price_type" type="SR\StackExchange\Plugin\Catalog\Model\Config\Source\Product\Options\Price" sortOrder="1"/>
    </type>
</config>

SR/StackExchange/Plugin/Catalog/Model/Config/Source/Product/Options/Price.php

namespace SR\StackExchange\Plugin\Catalog\Model\Config\Source\Product\Options;

class Price
{
    /**
     * {@inheritdoc}
     *
     * @codeCoverageIgnore
     */
    public function afterToOptionArray(
        \Magento\Catalog\Model\Config\Source\Product\Options\Price $subject,
        array  $priceTypeOption
    ){
        $priceTypeOption[] = ['value' => 'new_type', 'label' => __('New Type')];
        return $priceTypeOption;
    }
}

Clear magento cache.