Magento 2: Create Custom Linked Product type

Create a Module named Jeff_CustomLinked

registration.php:

<?php
    \Magento\Framework\Component\ComponentRegistrar::register(
        \Magento\Framework\Component\ComponentRegistrar::MODULE,
        'Jeff_CustomLinked',
        __DIR__
    );

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="Jeff_CustomLinked" setup_version="0.0.1"/>
</config>

Set up a InstallData script

Setup/InstallData.php:

<?php
namespace Jeff\CustomLinked\Setup;

class InstallData implements \Magento\Framework\Setup\InstallDataInterface
{
    public function install(\Magento\Framework\Setup\ModuleDataSetupInterface $setup, \Magento\Framework\Setup\ModuleContextInterface $context)
    {
        $data = [
            ['link_type_id' => \Jeff\CustomLinked\Model\Product\Link::LINK_TYPE_CUSTOMLINKED, 'code' => 'customlinked'],
        ];

        foreach($data as $bind) {
            $setup->getConnection()->insertForce($setup->getTable('catalog_product_link_type'), $bind);
        }

        $data = [
            [
                'link_type_id' => \Jeff\CustomLinked\Model\Product\Link::LINK_TYPE_CUSTOMLINKED,
                'product_link_attribute_code' => 'position',
                'data_type' => 'int',
            ]
        ];

        $setup->getConnection()->insertMultiple($setup->getTable('catalog_product_link_attribute'), $data);
    }
}

Model/Product.php:

<?php
namespace Jeff\CustomLinked\Model;
/**
 * Class \Magento\Catalog\Model\ProductLink\CollectionProvider\Related
 *
 */
class Product Extends \Magento\Catalog\Model\Product
{
    const LINK_TYPE_CUSTOMLINKED = 17;
    /**
     * Retrieve array of related products
     *
     * @return array
     */
    public function getCustomlinkedProducts()
    {
        if (!$this->hasCustomlinkedProducts()) {
            $products = [];
            $collection = $this->getCustomlinkedProductCollection();
            foreach ($collection as $product) {
                $products[] = $product;
            }
            $this->setCustomlinkedProducts($products);
        }
        return $this->getData('customlinked_products');
    }
    /**
     * Retrieve related products identifiers
     *
     * @return array
     */
    public function getCustomlinkedProductIds()
    {
        if (!$this->hasCustomlinkedProductIds()) {
            $ids = [];
            foreach ($this->getCustomlinkedProducts() as $product) {
                $ids[] = $product->getId();
            }
            $this->setCustomlinkedProductIds($ids);
        }
        return [$this->getData('customlinked_product_ids')];
    }
    /**
     * Retrieve collection related product
     *
     * @return \Magento\Catalog\Model\ResourceModel\Product\Link\Product\Collection
     */
    public function getCustomlinkedProductCollection()
    {
        $collection = $this->getLinkInstance()->setLinkTypeId(static::LINK_TYPE_CUSTOMLINKED)->getProductCollection()->setIsStrongMode();
        $collection->setProduct($this);
        return $collection;
    }
}

Model/Product/Link.php:

<?php
namespace Jeff\CustomLinked\Model\Product;

class Link extends \Magento\Catalog\Model\Product\Link
{
    const LINK_TYPE_CUSTOMLINKED = 17;
}

Model/ProductLink/CollectionProvider/CustomLinked.php:

<?php
namespace Jeff\CustomLinked\Model\ProductLink\CollectionProvider;

class Customlinked {
    public function getLinkedProducts($product) {
        return $product->getCustomlinkedProducts();
    }
}

etc/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\Product\LinkTypeProvider">
        <arguments>
            <argument name="linkTypes" xsi:type="array">
                <item name="customlinked" xsi:type="const">Jeff\CustomLinked\Model\Product\Link::LINK_TYPE_CUSTOMLINKED</item>
            </argument>
        </arguments>
    </type>

    <type name="Magento\Catalog\Model\ProductLink\CollectionProvider">
        <arguments>
            <argument name="providers" xsi:type="array">
                <item name="customlinked" xsi:type="object">Jeff\CustomLinked\Model\ProductLink\CollectionProvider\Customlinked</item>
            </argument>
        </arguments>
    </type>
</config>

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\Ui\DataProvider\Product\Form\Modifier\Related">
        <plugin name="custom_change_modifyMeta_after" type="Jeff\CustomLinked\Plugin\Related" />
    </type>
    <type name="Jeff\CustomLinked\Model\ProductLink\CollectionProvider\Customlinked">
        <plugin name="change_link_befoer" type="Jeff\CustomLinked\Plugin\Related" />
    </type>
</config>

Ui Component Data Provider

Ui/DataProvider/Product/Related/CustomLinkedDataProvider.php:

<?php
namespace Jeff\CustomLinked\Ui\DataProvider\Product\Related;

class CustomlinkedDataProvider extends \Magento\Catalog\Ui\DataProvider\Product\Related\AbstractDataProvider
{
    protected function getLinkType() {
        return 'clustomlinked';
    }
}

Plugin for product related grid

Plugin/Related.php:

<?php
namespace Jeff\CustomLinked\Plugin;

use Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\Related as RelatedParent;
use Magento\Ui\Component\Form\Fieldset;

class Related extends RelatedParent {
    const GROUP_RELATED = 'related';
    const DATA_SCOPE_CUSTOMLINKED = 'customlinked';
    private $priceModifier;
    protected $product;
    public function afterModifyMeta($modify, $result) {
        if (isset($result[static::GROUP_RELATED]['children'])) {
            $result[static::GROUP_RELATED]['children'][$modify->scopePrefix . static::DATA_SCOPE_CUSTOMLINKED] = $this->getCustomlinkedFieldset($modify);
        }
        return $result;
    }
    /**
     * Get price modifier
     *
     * @return \Magento\Catalog\Ui\Component\Listing\Columns\Price
     * @deprecated 101.0.0
     */
    private function getPriceModifier($modify) {
        if (!$this->priceModifier) {
            $this->priceModifier = \Magento\Framework\App\ObjectManager::getInstance()->get(
                    \Magento\Catalog\Ui\Component\Listing\Columns\Price::class
            );
        }
        return $this->priceModifier;
    }
    /**
     * Prepares config for the Related products fieldset
     *
     * @return array
     * @since 101.0.0
     */
    protected function getCustomlinkedFieldset($modify) {
        $content = __(
                'My Custom Linked Product.'
        );
        return [
            'children' => [
                'button_set' => $modify->getButtonSet(
                        $content, __('Add Custom Linked'), $modify->scopePrefix . static::DATA_SCOPE_CUSTOMLINKED
                ),
                'modal' => $this->getGenericModal(
                        __('Add Custom Linked'), $modify->scopePrefix . static::DATA_SCOPE_CUSTOMLINKED
                ),
                static::DATA_SCOPE_CUSTOMLINKED => $this->getGrid($modify->scopePrefix . static::DATA_SCOPE_CUSTOMLINKED),
            ],
            'arguments' => [
                'data' => [
                    'config' => [
                        'additionalClasses' => 'admin__fieldset-section',
                        'label' => __('Custom Linked'),
                        'collapsible' => false,
                        'componentType' => Fieldset::NAME,
                        'dataScope' => '',
                        'sortOrder' => 11,
                    ],
                ],
            ]
        ];
    }
    public function afterModifyData($modify , $data)
    {
        $product = $modify->locator->getProduct();
        $productId = $product->getId();
        if (!$productId) {
            return $data;
        }
        $priceModifier = $this->getPriceModifier($modify);
        /**
         * Set field name for modifier
         */
        $priceModifier->setData('name', 'price');
        $dataScopes = $this->getDataScopes();
        $dataScopes[] = static::DATA_SCOPE_CUSTOMLINKED;
        foreach ($dataScopes as $dataScope) {
            if($dataScope == static::DATA_SCOPE_CUSTOMLINKED){
            $data[$productId]['links'][$dataScope] = [];
            foreach ($modify->productLinkRepository->getList($product) as $linkItem) {
                if ($linkItem->getLinkType() !== $dataScope) {
                    continue;
                }
                /** @var \Magento\Catalog\Model\Product $linkedProduct */
                $linkedProduct = $modify->productRepository->get(
                    $linkItem->getLinkedProductSku(),
                    false,
                    $modify->locator->getStore()->getId()
                );
                $data[$productId]['links'][$dataScope][] = $this->fillData($linkedProduct, $linkItem);
            }
            if (!empty($data[$productId]['links'][$dataScope])) {
                $dataMap = $priceModifier->prepareDataSource([
                    'data' => [
                        'items' => $data[$productId]['links'][$dataScope]
                    ]
                ]);
                $data[$productId]['links'][$dataScope] = $dataMap['data']['items'];
            }
        }
        }
        
        return $data;
    }
    public function beforeGetLinkedProducts($provider, $product) {
        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $this->product = $objectManager->create('Jeff\CustomLinked\Model\Product');
        $currentProduct = $this->product->load($product->getId());
        return [$currentProduct];
    }
}

ui component xml configuration

view/adminhtml/ui_component/customlinked_product_listing.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<listing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <argument name="data" xsi:type="array">
        <item name="js_config" xsi:type="array">
            <item name="provider" xsi:type="string">customlinked_product_listing.customlinked_product_listing_data_source
            </item>
            <item name="deps" xsi:type="string">customlinked_product_listing.customlinked_product_listing_data_source</item>
        </item>
        <item name="spinner" xsi:type="string">product_columns</item>
        <item name="acl" xsi:type="string">Magento_Catalog::products</item>
    </argument>
    <dataSource name="customlinked_product_listing_data_source">
        <argument name="dataProvider" xsi:type="configurableObject">
            <argument name="class" xsi:type="string">Jeff\CustomLinked\Ui\DataProvider\Product\Related\CustomlinkedDataProvider</argument>
            <argument name="name" xsi:type="string">customlinked_product_listing_data_source</argument>
            <argument name="primaryFieldName" xsi:type="string">entity_id</argument>
            <argument name="requestFieldName" xsi:type="string">id</argument>
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="component" xsi:type="string">Magento_Ui/js/grid/provider</item>
                    <item name="update_url" xsi:type="url" path="mui/index/render"/>
                    <item name="storageConfig" xsi:type="array">
                        <item name="cacheRequests" xsi:type="boolean">false</item>
                    </item>
                </item>
            </argument>
        </argument>
    </dataSource>
    <listingToolbar name="listing_top">
        <filters name="listing_filters">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="statefull" xsi:type="array">
                        <item name="applied" xsi:type="boolean">false</item>
                    </item>
                    <item name="params" xsi:type="array">
                        <item name="filters_modifier" xsi:type="array" />
                    </item>
                    <item name="observers" xsi:type="array">
                        <item name="filters" xsi:type="object">Magento\Catalog\Ui\Component\Listing\Filters</item>
                    </item>
                </item>
            </argument>
        </filters>
        <paging name="listing_paging"/>
    </listingToolbar>
    <columns name="product_columns" class="Magento\Catalog\Ui\Component\Listing\Columns">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="childDefaults" xsi:type="array">
                    <item name="fieldAction" xsi:type="array">
                        <item name="provider" xsi:type="string">customlinkedProductGrid</item>
                        <item name="target" xsi:type="string">selectProduct</item>
                        <item name="params" xsi:type="array">
                            <item name="0" xsi:type="string">${ $.$data.rowIndex }</item>
                        </item>
                    </item>
                </item>
            </item>
        </argument>
        <selectionsColumn name="ids">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="indexField" xsi:type="string">entity_id</item>
                    <item name="sortOrder" xsi:type="number">0</item>
                    <item name="preserveSelectionsOnFilter" xsi:type="boolean">true</item>
                </item>
            </argument>
        </selectionsColumn>
        <column name="entity_id">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">textRange</item>
                    <item name="sorting" xsi:type="string">asc</item>
                    <item name="label" xsi:type="string" translate="true">ID</item>
                    <item name="sortOrder" xsi:type="number">10</item>
                </item>
            </argument>
        </column>
        <column name="thumbnail" class="Magento\Catalog\Ui\Component\Listing\Columns\Thumbnail">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="component" xsi:type="string">Magento_Ui/js/grid/columns/thumbnail</item>
                    <item name="add_field" xsi:type="boolean">true</item>
                    <item name="sortable" xsi:type="boolean">false</item>
                    <item name="altField" xsi:type="string">name</item>
                    <item name="has_preview" xsi:type="string">1</item>
                    <item name="align" xsi:type="string">left</item>
                    <item name="label" xsi:type="string" translate="true">Thumbnail</item>
                    <item name="sortOrder" xsi:type="number">20</item>
                </item>
            </argument>
        </column>
        <column name="name">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">text</item>
                    <item name="add_field" xsi:type="boolean">true</item>
                    <item name="label" xsi:type="string" translate="true">Name</item>
                    <item name="sortOrder" xsi:type="number">30</item>
                </item>
            </argument>
        </column>
        <column name="attribute_set_id">
            <argument name="data" xsi:type="array">
                <item name="options" xsi:type="object">Magento\Catalog\Model\Product\AttributeSet\Options</item>
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">select</item>
                    <item name="component" xsi:type="string">Magento_Ui/js/grid/columns/select</item>
                    <item name="dataType" xsi:type="string">select</item>
                    <item name="label" xsi:type="string" translate="true">Attribute Set</item>
                    <item name="sortOrder" xsi:type="number">40</item>
                </item>
            </argument>
        </column>
        <column name="attribute_set_text" class="Magento\Catalog\Ui\Component\Listing\Columns\AttributeSetText">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="sortOrder" xsi:type="number">41</item>
                    <item name="label" xsi:type="string" translate="true">AttributeSetText</item>
                    <item name="visible" xsi:type="boolean">false</item>
                </item>
            </argument>
        </column>
        <column name="status">
            <argument name="data" xsi:type="array">
                <item name="options" xsi:type="object">Magento\Catalog\Model\Product\Attribute\Source\Status</item>
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">select</item>
                    <item name="component" xsi:type="string">Magento_Ui/js/grid/columns/select</item>
                    <item name="dataType" xsi:type="string">select</item>
                    <item name="label" xsi:type="string" translate="true">Status</item>
                    <item name="sortOrder" xsi:type="number">50</item>
                </item>
            </argument>
        </column>
        <column name="status_text" class="Magento\Catalog\Ui\Component\Listing\Columns\StatusText">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="sortOrder" xsi:type="number">51</item>
                    <item name="label" xsi:type="string" translate="true">StatusText</item>
                    <item name="visible" xsi:type="boolean">false</item>
                </item>
            </argument>
        </column>
        <column name="type_id">
            <argument name="data" xsi:type="array">
                <item name="options" xsi:type="object">Magento\Catalog\Model\Product\Type</item>
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">select</item>
                    <item name="component" xsi:type="string">Magento_Ui/js/grid/columns/select</item>
                    <item name="dataType" xsi:type="string">select</item>
                    <item name="label" xsi:type="string" translate="true">Type</item>
                    <item name="sortOrder" xsi:type="number">60</item>
                </item>
            </argument>
        </column>
        <column name="sku">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">text</item>
                    <item name="label" xsi:type="string" translate="true">SKU</item>
                    <item name="sortOrder" xsi:type="number">70</item>
                </item>
            </argument>
        </column>
        <column name="price" class="Magento\Catalog\Ui\Component\Listing\Columns\Price">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">textRange</item>
                    <item name="add_field" xsi:type="boolean">true</item>
                    <item name="label" xsi:type="string" translate="true">Price</item>
                    <item name="sortOrder" xsi:type="number">80</item>
                </item>
            </argument>
        </column>
    </columns>
</listing>

After following all these steps as above, you can add your custom linked products to any product shown as following image:

You can download the source code at My GitHub