How to get all the products from category in magento 2

Question

I want to get all the products from Category, and its child categories in magento 2 How can i get that? I have some products assign to main category whereas some assign to child categories. i want to get all product collection.

Answer 1

Here is one way to do this using a custom module, in this case I used my Page module with a new Block and Template. I called it from a static block in cms.

Parent category is specified in the template. The product collection returns all products in parent and child categories.

Block : Gaiterjones\Page\Block\GetAllProductsInCategory

<?php
namespace Gaiterjones\Page\Block;

use Magento\Framework\View\Element\Template\Context;
use Magento\Catalog\Model\CategoryFactory;
use Magento\Catalog\Model\ResourceModel\Product\CollectionFactory as ProductCollectionFactory;

class GetAllProductsInCategory extends \Magento\Framework\View\Element\Template
{
        protected $_categoryFactory;
        protected $_productCollectionFactory;

    public function __construct(
        Context $context,
        CategoryFactory $categoryFactory,
        ProductCollectionFactory $productCollectionFactory,
        array $data = []
    )
    {
        $this->_categoryFactory = $categoryFactory;
        $this->_productCollectionFactory = $productCollectionFactory;
        parent::__construct($context, $data);
    }

    public function _prepareLayout()
    {
        return parent::_prepareLayout();
    }

    public function getAllCategoryProducts($_categoryID)
    {
        return $this->getProductCollection($_categoryID);
    }

    public function getProductCollection($_categoryID)
    {
        // get products in category and all child categories
        //
        $_category=$this->_categoryFactory->create()->load($_categoryID);
        $_categoriesFilter = [
            'eq' => $_category->getAllChildren(true)
        ];

        $_productCollection = $this->_productCollectionFactory->create();
        $_productCollection->addCategoriesFilter($_categoriesFilter);
        $_productCollection->addAttributeToSelect('*');

        return $_productCollection;
    }

}
?>

Template : view\frontent\templates\getallproductsincategory.phtml

<?php
$parentCategoryId = 20;
$productCollection = $block->getProductCollection($parentCategoryId);

?>
<div>
    <ol class="row list">
        <?php foreach ($productCollection as $product): ?>
            <li>
                <span><?php echo $product->getSku(). ' - '. $product->getName() ?></span>
            </li>
        <?php endforeach; ?>
    </ol>
</div>

cms static block

{{block class="Gaiterjones\Page\Block\GetAllProductsInCategory" template="Gaiterjones_Page::getallproductsincategory.phtml"}}