Magento2 – Attribute Not Shown in Layer Navigation After Migration

As I said, solution was quite easy once I realized what the problem was.

I followed this Magento Wiki to setup attributeSets and attributes, only I didn't realize my attributes had to be of 'int' backend-type to be eligible for layered navigation.

So, in order to create an attribute for layered navigation you must have into consideration:

• Frontend-type must be price, select or multiselect

• Backend-type must be decimal (like price), int (for selects), varchar (for multiselect). There's no need to worry about this unless you are, like me, creating attributes programmatically.

• That it must be marked as 'use in Layered Navigation'

• That there should be at least two products with different values for this attribute (this seems to be not mandatory, but gives sense to use the attribute in Layered Navigation)

There are 2 methods to achieve this

First one

Filter.php (api model)

    public function __construct(\Magento\Framework\Webapi\Rest\Request 
        $request){

                $this->_request         = $request;
        }


/**
     * Retrieve filterlist
     *
     * @api
     * @return array
     */
    public function retrieve(){     

        $category = $this->_request->getParam('categoryId');

        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();

        $filterableAttributes = $objectManager->getInstance()->get(\Magento\Catalog\Model\Layer\Category\FilterableAttributeList::class);

        $appState = $objectManager->getInstance()->get(\Magento\Framework\App\State::class);
        $layerResolver = $objectManager->getInstance()->get(\Magento\Catalog\Model\Layer\Resolver::class);
        $filterList = $objectManager->getInstance()->create(
            \Magento\Catalog\Model\Layer\FilterList::class,
                [
                    'filterableAttributes' => $filterableAttributes
                ]
            );      

            $layer = $layerResolver->get();
            $layer->setCurrentCategory($category);
            $filters = $filterList->getFilters($layer);
            $maxPrice = $layer->getProductCollection()->getMaxPrice();
            $minPrice = $layer->getProductCollection()->getMinPrice();  

        $i = 0;
       foreach($filters as $filter)
       {
           //$availablefilter = $filter->getRequestVar(); //Gives the request param name such as 'cat' for Category, 'price' for Price
           $availablefilter = (string)$filter->getName(); //Gives Display Name of the filter such as Category,Price etc.
           $items = $filter->getItems(); //Gives all available filter options in that particular filter
           $filterValues = array();
           $j = 0;
           foreach($items as $item)
           {


               $filterValues[$j]['display'] = strip_tags($item->getLabel());
               $filterValues[$j]['value']   = $item->getValue();
               $filterValues[$j]['count']   = $item->getCount(); //Gives no. of products in each filter options
               $j++;
           }
           if(!empty($filterValues) && count($filterValues)>1)
           {
               $filterArray['availablefilter'][$availablefilter] =  $filterValues;
           }
           $i++;
       }  


        echo json_encode($filterArray);
        exit;

    }

Sample out put of this code will be:

{
    "availablefilter": {
        "Climate": [
            {
                "display": "All-Weather",
                "value": "202",
                "count": "1"
            },
            {
                "display": "Cool",
                "value": "204",
                "count": "1"
            }
        ],
        "Manufacturer": [
            {
                "display": "Azzedine Alaïa",
                "value": "216",
                "count": "1"
            },
            {
                "display": "Balenciaga",
                "value": "217",
                "count": "1"
            }
        ],
        "Material": [
            {
                "display": "Cotton",
                "value": "33",
                "count": "1"
            },
            {
                "display": "Nylon",
                "value": "37",
                "count": "1"
            }
        ],

Second method

public function __construct(
        \Magento\Catalog\Model\ResourceModel\Product\Attribute\CollectionFactory $productAttributeCollectionFactory
    ) {
        $this->productAttributeCollectionFactory = $productAttributeCollectionFactory;
    }

    public function getFilterableAttributes()
    {
        /** @var \Magento\Catalog\Model\ResourceModel\Product\Attribute\Collection $productAttributes */
        $productAttributes = $this->productAttributeCollectionFactory->create();
        $productAttributes->addFieldToFilter(
            ['is_filterable', 'is_filterable_in_search'],
            [[1, 2], 1]
        );

        return $productAttributes;
    }