In magento 2 admin custom field value stored in db but when edit a product edit page custom field came empty, how to solve this

Question

app/code/Cm/Preoder/view/adminhtml/ui_component/product_form.xml

<?xml version="1.0" encoding="UTF-8"?>
<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <modal name="advanced_inventory_modal">
        <fieldset name="stock_data">
            <container name="container_backorders">
                <field name="backorders">
                    <argument name="data" xsi:type="array">
                        <item name="config" xsi:type="array">
                            <item name="component" xsi:type="string">Cm_Preorder/js/backorders</item>
                        </item>
                    </argument>
                </field>
             </container>
                <field name="preorder_button">
                    <argument name="data" xsi:type="array">
                        <item name="config" xsi:type="array">
                            <item name="dataType" xsi:type="string">text</item>
                            <item name="label" xsi:type="string" translate="true"> Pre-Order Cart Button</item>
                            <item name="scopeLabel" xsi:type="string">[Store view]</item>
                            <item name="formElement" xsi:type="string">input</item>
                            <item name="source" xsi:type="string">model</item>
                            <item name="sortOrder" xsi:type="number">801</item>
                            <item name="dataScope" xsi:type="string">preorder_button</item>
                        </item>
                    </argument>
                </field>
                <field name="preorder_note">
                    <argument name="data" xsi:type="array">
                        <item name="config" xsi:type="array">
                            <item name="dataType" xsi:type="string">text</item>
                            <item name="label" xsi:type="string" translate="true">  Pre-Order Note</item>
                            <item name="scopeLabel" xsi:type="string">[Store view]</item>
                            <item name="formElement" xsi:type="string">input</item>
                            <item name="source" xsi:type="string">model</item>
                            <item name="sortOrder" xsi:type="number">802</item>
                            <item name="dataScope" xsi:type="string">preorder_note</item>
                        </item>
                    </argument>
                </field>
            </fieldset>
    </modal>
</form>

app/code/Cm/Preorder/etc/adminhtml/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="catalog_product_save_after">
        <observer name="preorder" instance="Cm\Preorder\Observer\ProductSaveAfter" />
    </event>
</config>

app/code/Cm/Preoder/Observer/ProductSaveAfter.php

<?php
namespace Cm\Preorder\Observer;

use \Magento\Framework\Event\ObserverInterface;
use \Magento\Framework\Event\Observer as EventObserver;

class ProductSaveAfter implements ObserverInterface
{
     protected $_scopeConfig;
     protected $_request;
     protected $_objectManager;


     public function __construct(
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig,
        \Magento\Framework\App\RequestInterface $request,
        \Magento\Framework\ObjectManagerInterface $objectmanager


    ) {
        $this->_objectManager = $objectmanager;
        $this->_scopeConfig = $scopeConfig;
        $this->_request = $request;

    }

    public function execute(\Magento\Framework\Event\Observer $observer)
    {

         $_product = $observer->getProduct();  // you will get product object 
        $product_id = $_product->getId();
        $preorder_button=$_product->getPreorderButton(); 
        $preorder_note=$_product->getPreorderNote();
        $resource = $this->_objectManager->get('Magento\Framework\App\ResourceConnection');
        $query = "SELECT * FROM `cataloginventory_stock_item` WHERE  `product_id`=$product_id";
        $connection = $resource->getConnection();
         $res = $connection->fetchAll($query);
        if($res)
            {
               $var = array_column($res, 'product_id');
                $key = key($var);
                $id = $var[$key];
                $sql = "UPDATE `cataloginventory_stock_item` SET preorder_button = '$preorder_button' , preorder_note ='$preorder_note'  WHERE product_id = ".$id;
                $connection->query($sql);
            }
          }
}

In product edit form, custom field shows empty after value saved in db

Saved value

Answer 1

Try using plugin how you save:

app/code/SR/MagentoCommunity/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\CatalogInventory\Model\Stock\StockItemRepository">
        <plugin name="sr_update_stock_item"
                type="SR\MagentoCommunity\Plugin\CatalogInventory\Model\Stock\StockItemRepository" sortOrder="1"/>
    </type>
</config>

app/code/SR/MagentoCommunity/Plugin/CatalogInventory/Model/Stock/StockItemRepository.php

<?php
namespace SR\MagentoCommunity\Plugin\CatalogInventory\Model\Stock;

use Magento\CatalogInventory\Model\ResourceModel\Stock\Item as StockItemResource;
use Magento\Framework\Registry;

class StockItemRepository
{
    /**
     * @var StockItemResource
     */
    private $resource;

    /**
     * @var Registry
     */
    private $registry;

    /**
     * StockItemRepository constructor.
     *
     * @param StockItemResource $resource
     * @param Registry $registry
     */
    public function __construct(
        StockItemResource $resource,
        Registry $registry
    ) {
        $this->resource = $resource;
        $this->registry = $registry;
    }

    public function afterSave(
        \Magento\CatalogInventory\Model\Stock\StockItemRepository $subject,
        $stockItem
    ) {
        $product = $this->registry->registry('product');
        $preorderButton = $product->getData('preorder_button');
        $preorderNote = $product->getData('preorder_note');
        $needSave = false;
        $newStockItem = $stockItem;
        if ($preorderButton) {
            $newStockItem->setPreorderButton($preorderButton);
            $needSave = true;
        }
        if ($preorderNote) {
            $newStockItem->setPreorderNote($preorderNote);
            $needSave = true;
        }

        if ($needSave) {
            $this->resource->save($newStockItem);
        }

        return $stockItem;
    }
}

How populate when edit:

app/code/SR/MagentoCommunity/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\CatalogInventory\Ui\DataProvider\Product\Form\Modifier\AdvancedInventory">
        <plugin name="sr_load_stock_item"
                type="SR\MagentoCommunity\Plugin\CatalogInventory\Ui\DataProvider\Product\Form\Modifier\AdvancedInventory" sortOrder="1"/>
    </type>
</config>

app/code/SR/MagentoCommunity/Plugin/CatalogInventory/Ui/DataProvider/Product/Form/Modifier/AdvancedInventory.php

<?php
namespace SR\MagentoCommunity\Plugin\CatalogInventory\Ui\DataProvider\Product\Form\Modifier;

use Magento\CatalogInventory\Model\Stock\StockItemRepository;

class AdvancedInventory
{
    /**
     * @var StockItemRepository
     */
    private $stockItemRepository;

    /**
     * AdvancedInventory constructor.
     *
     * @param StockItemRepository $stockItemRepository
     */
    public function __construct(
        StockItemRepository $stockItemRepository
    ) {
        $this->stockItemRepository = $stockItemRepository;
    }

    public function afterModifyData(
        \Magento\CatalogInventory\Ui\DataProvider\Product\Form\Modifier\AdvancedInventory $subject,
        $data
    ) {
        foreach ($data as &$product) {
            if (isset($product['product']['stock_data']) && isset($product['product']['stock_data']['item_id'])) {
                $itemId = $product['product']['stock_data']['item_id'];
                if ($itemId) {
                    try {
                        $item = $this->stockItemRepository->get($itemId);
                        $product['product']['preorder_button'] = $item->getData('preorder_button');
                        $product['product']['preorder_note'] = $item->getData('preorder_note');;
                    } catch (\Exception $e) {}
                }
            }
        }

        return $data;
    }
}