Order by position in product collection

Question

I'm trying to order products by position in category

public function __getProductCollection($category_id_array) {

    $collection = $this->_productCollectionFactory->create();
    $collection->addAttributeToSelect('*');
    $collection->addCategoriesFilter(['in' => $category_id_array]);
    $collection->addAttributeToFilter('visibility', \Magento\Catalog\Model\Product\Visibility::VISIBILITY_BOTH);
    $collection->addAttributeToFilter('status', \Magento\Catalog\Model\Product\Attribute\Source\Status::STATUS_ENABLED);
    //$collection->addAttributeToSort('position');
    $collection->setOrder('position','ASC');
    

    return $collection;
}

I got this error

 Unknown column 'cat_index_position' in 'order clause'

I tried also

$collection->setOrder('cat_index_position','ASC');

$collection->setOrder('cat_index.position','ASC');

But the ordering is not working

PS: i'm using Magento 2.2.4

Answer 1

I solved the problem

i added a class attribute _categoryFactory and used it in constructor

public function __construct(
\Magento\Catalog\Block\Product\Context $context
,\Magento\Catalog\Model\CategoryFactory $categoryFactory) {
    parent::__construct(
            $context, $data
    );
    $this->_categoryFactory = $categoryFactory;
}



public function __getProductCollection($category_id) {

    $products = $this->_categoryFactory->create()->load($category_id)->getProductCollection()->addAttributeToSelect('*')->setOrder('cat_index_position','ASC');
    return $products;
}