How to show categories in Layered Navigation magento 2 ( always )

Question

I am trying to add all categories in Layered Navigation after clicking on one to the categories.

Now I can see all in the first page, after clicking I can't see any categories in Layered Navigation.

Please check here below the pic.

Answer 1

You Need to Override Following Model Class :

Magento\CatalogSearch\Model\Layer\Filter\Category

Override by creating new Module and in di.xml file by following way :

<preference for="Magento\CatalogSearch\Model\Layer\Filter\Category" type="Vendor\Module\Model\Layer\Filter\Category" />

This is my overrided Model :

<?php

     namespace Vendor\Module\Model\Layer\Filter;

      use Magento\Catalog\Model\Layer\Filter\AbstractFilter;
      use Magento\Catalog\Model\Layer\Filter\DataProvider\Category as     CategoryDataProvider;

     class Category extends AbstractFilter
     {
    /**
     * @var \Magento\Framework\Escaper
     */
    private $escaper;

    /**
     * @var CategoryDataProvider
     */
    private $dataProvider;
    protected $_logger;
    /**
     * @param \Magento\Catalog\Model\Layer\Filter\ItemFactory $filterItemFactory
     * @param \Magento\Store\Model\StoreManagerInterface $storeManager
     * @param \Magento\Catalog\Model\Layer $layer
     * @param \Magento\Catalog\Model\Layer\Filter\Item\DataBuilder $itemDataBuilder
     * @param \Magento\Catalog\Model\CategoryFactory $categoryFactory
     * @param \Magento\Framework\Escaper $escaper
     * @param CategoryManagerFactory $categoryManager
     * @param array $data
     */
    public function __construct(   
        \Magento\Catalog\Model\Layer\Filter\ItemFactory $filterItemFactory,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Magento\Catalog\Model\Layer $layer,
        \Magento\Catalog\Model\Layer\Filter\Item\DataBuilder $itemDataBuilder,
        \Magento\Framework\Escaper $escaper,
        \Magento\Catalog\Model\Layer\Filter\DataProvider\CategoryFactory $categoryDataProviderFactory,
        \Psr\Log\LoggerInterface $logger, //log injection

        array $data = []
    ) {
        parent::__construct(
            $filterItemFactory,
            $storeManager,
            $layer,
            $itemDataBuilder,
            $data
        );
        $this->escaper = $escaper;
        $this->_requestVar = 'cat';
        $this->dataProvider = $categoryDataProviderFactory->create(['layer' => $this->getLayer()]);
        $this->_logger = $logger;
    }

    /**
     * Apply category filter to product collection
     *
     * @param   \Magento\Framework\App\RequestInterface $request
     * @return  $this
     */
    public function apply(\Magento\Framework\App\RequestInterface $request)
    {
        $categoryId = $request->getParam($this->_requestVar) ?: $request->getParam('id');
        if (empty($categoryId)) {
            return $this;
        }

        $this->dataProvider->setCategoryId($categoryId);

        $category = $this->dataProvider->getCategory();

        $this->getLayer()->getProductCollection()->addCategoryFilter($category);

        if ($request->getParam('id') != $category->getId() && $this->dataProvider->isValid()) {
            $this->getLayer()->getState()->addFilter($this->_createItem($category->getName(), $categoryId));
        }
        return $this;
    }

    /**
     * Get filter value for reset current filter state
     *
     * @return mixed|null
     */
    public function getResetValue()
    {
        return $this->dataProvider->getResetValue();
    }

    /**
     * Get filter name
     *
     * @return \Magento\Framework\Phrase
     */
    public function getName()
    {
        return __('Category');
    }

    /**
     * Get data array for building category filter items
     *
     * @return array
     */
    protected function _getItemsData()
    {
        $_objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $productCollection = $this->getLayer()->getProductCollection();

        $category = $this->dataProvider->getCategory();

        $optionsFacetedData = $productCollection->getFacetedData('category');
        $categories = $category->getChildrenCategories();
        $collectionSize = $productCollection->getSize();

        if ($category->getIsActive()) {
            foreach ($categories as $category) {
                if ($category->getIsActive()
                    && isset($optionsFacetedData[$category->getId()])
                    && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                ) {
                    $this->itemDataBuilder->addItemData(
                        $this->escaper->escapeHtml($category->getName().'%level-1%'.$category->getParentId()),
                        $category->getId(),
                        $optionsFacetedData[$category->getId()]['count']
                    );
                }
                    $cat = $_objectManager->create('Magento\Catalog\Model\Category')->load($category->getId());
                    $sub_category = $cat->getChildrenCategories();

                    foreach ($sub_category as $category) {
                        if ($category->getIsActive()
                                && isset($optionsFacetedData[$category->getId()])
                                && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                            ) 
                        {
                            $this->itemDataBuilder->addItemData(
                                $this->escaper->escapeHtml($category->getName().'%level-2%'.$category->getParentId()),
                                $category->getId(),
                                $optionsFacetedData[$category->getId()]['count']
                            );
                        }
                        $cat = $_objectManager->create('Magento\Catalog\Model\Category')->load($category->getId());
                        $sub_category = $cat->getChildrenCategories();

                        foreach ($sub_category as $category) {
                            if ($category->getIsActive()
                                    && isset($optionsFacetedData[$category->getId()])
                                    && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                                ) 
                            {
                                $this->itemDataBuilder->addItemData(
                                    $this->escaper->escapeHtml($category->getName().'%level-3%'.$category->getParentId()),
                                    $category->getId(),
                                    $optionsFacetedData[$category->getId()]['count']
                                );
                            }

                            $cat = $_objectManager->create('Magento\Catalog\Model\Category')->load($category->getId());
                            $sub_category = $cat->getChildrenCategories();

                            foreach ($sub_category as $category) {
                                if ($category->getIsActive()
                                        && isset($optionsFacetedData[$category->getId()])
                                        && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                                    ) 
                                {
                                    $this->itemDataBuilder->addItemData(
                                        $this->escaper->escapeHtml($category->getName().'%level-4%'.$category->getParentId()),
                                        $category->getId(),
                                        $optionsFacetedData[$category->getId()]['count']
                                    );
                                }

                                $cat = $_objectManager->create('Magento\Catalog\Model\Category')->load($category->getId());
                                $sub_category = $cat->getChildrenCategories();

                                foreach ($sub_category as $category) {
                                    if ($category->getIsActive()
                                            && isset($optionsFacetedData[$category->getId()])
                                            && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                                        ) 
                                    {
                                        $this->itemDataBuilder->addItemData(
                                            $this->escaper->escapeHtml($category->getName().'%level-5%'.$category->getParentId()),
                                            $category->getId(),
                                            $optionsFacetedData[$category->getId()]['count']
                                        );
                                    }

                                            $cat = $_objectManager->create('Magento\Catalog\Model\Category')->load($category->getId());
                                            $sub_category = $cat->getChildrenCategories();

                                            foreach ($sub_category as $category) {
                                                if ($category->getIsActive()
                                                        && isset($optionsFacetedData[$category->getId()])
                                                        && $this->isOptionReducesResults($optionsFacetedData[$category->getId()]['count'], $collectionSize)
                                                    ) 
                                                {
                                                    $this->itemDataBuilder->addItemData(
                                                        $this->escaper->escapeHtml($category->getName().'%level-6%'.$category->getParentId()),
                                                        $category->getId(),
                                                        $optionsFacetedData[$category->getId()]['count']
                                                    );
                                                }
                                            }
                                }
                            }
                        }
                    }
            }
        }
        return $this->itemDataBuilder->build();
    }
    }