How to get products of a category and all its subcategories by category id?

Question

I am trying to get all products of specific category whether these products are directly listed in the category or in the subcategories under this specific category I really searched for this on google and Magento Stack Exchange and found nothing about Magento 2, all I found are some topics on Magento 1,

Here is What I just reached,

use Magento\Framework\App\Action\Action;
use Magento\Framework\App\Action\Context;
use Magento\Framework\Controller\Result\JsonFactory;
use Magento\Catalog\Model\ResourceModel\Product\CollectionFactory;

class ChildProducts extends Action
{
    protected $resultJsonFactory;
    protected $_categoryFactory;
    protected $productCollectionFactory;
    public function __construct(Context $context, JsonFactory $jsonFactory ,\Magento\Catalog\Model\CategoryFactory $categoryFactory ,
    CollectionFactory $productCollection)
    {
        $this->_categoryFactory = $categoryFactory;
        $this->resultJsonFactory = $jsonFactory;
        $this->productCollectionFactory = $productCollection;
        parent::__construct($context);
    }

    public function execute()
    {
        // get parent category
        $categoryId = $this->getRequest()->getParam('category_id');


        $productCollection = $this->productCollectionFactory->create();
        $productCollection->addAttributeToSelect('*');
        $productCollection->addCategoriesFilter(array('in' => $categoryId));
        return $this->resultJsonFactory->create()->setData($productCollection);
    }

Answer 1

Inject \Magento\Catalog\Api\CategoryManagementInterface $obj in to your file and create object $this->_obj

Then in your method use this object to get tree

if(your category_id)
        {
            $depth = 5;
            $cat = $this->_obj->getTree("your category_id", $depth);
            $this->getSubCategories($cat);
        }

Create a Recursive fuction name public function getSubCategories($child_detail)

     public function getSubCategories($child_detail)
            {
                $subCats = $child_detail->getChildrenData();
                       if ($subCats) {

                    foreach ($subCats as $subcat) {
                            //your category tree with subcategories
                              echo  $child_name = $subcat->getName();

        //for products in a category inject di of class ***\Magento\Framework\App\ResourceConnection $resourceConnection*** use it with object ***$this->_resources***

                                  $connection= $this->_resources->getConnection();

        //create a custom query to get all products along with their child products otherwise child products won't appear

                                 $select = $connection->select()
                                     ->from(['o' =>  $this->_resources->getTableName('catalog_category_product')]);
                                 $select->where('category_id = ?', $subcat->getId());

                                 $result = $connection->fetchAll($select);


//All category product_ids are in $result to deal it with separate save separately
                                 $proIds = array();
                                 foreach ($result as $product)
                                 {
                                     $proIds[] = $product['product_id'];
                                 }

//inject ***\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productFactory*** and create object ***$this->productFactory*** to load your category product from all products or you can say filter your products from all products
         $collect = $this->productFactory->create()->addFieldToFilter('entity_id',array('in',$proIds));
                                 foreach ($collect as $product)
                                 {
                                    //do what ever you like with product
                                   echo $product->getId();
                                 }

            $this->getSubCategories($subcat);
                    }

hope that helps

Answer 2

To get All Product Based On Category Id :-

protected $_productCollectionFactory;
protected $_categoryFactory;

public function __construct(
    \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory,
    \Magento\Catalog\Model\CategoryFactory $categoryFactory,
    \Magento\Framework\View\Element\Template\Context $context,
) {
    $this->_categoryFactory = $categoryFactory;
    $this->_productCollectionFactory = $productCollectionFactory;
    parent::__construct($context);
}

public function getProductCollection()
{
    $categoryId = 'yourcategoryid';
    $category = $this->_categoryFactory->create()->load($categoryId);
    $collection = $this->_productCollectionFactory->create();
    $collection->addAttributeToSelect('*');
    $collection->addCategoryFilter($category);
    return $collection;
}

Answer 3

here is what i just reached , all i needed to do to get all the products data from parent category and its all sub categories to the last level was that , here is the code

use Magento\Framework\App\Action\Action;
use Magento\Framework\App\Action\Context;
use Magento\Framework\Controller\Result\JsonFactory;
use Magento\Catalog\Model\ResourceModel\Product\CollectionFactory;
use Magento\Catalog\Api\CategoryManagementInterface;
use Magento\Catalog\Model\ResourceModel\Category\CollectionFactory as CategoryCollectionFactory;

class ChildProducts extends Action
{
    protected $resultJsonFactory;
    protected $_categoryFactory;
    protected $productCollectionFactory;
    protected $allProducts = [];
    protected $cats = [];
    protected $_obj;
    protected $categoryCollectionFactory;
    public function __construct(Context $context, JsonFactory $jsonFactory ,\Magento\Catalog\Model\CategoryFactory $categoryFactory ,
    CollectionFactory $productCollection , CategoryManagementInterface $obj ,
    CategoryCollectionFactory $categoryCollectionFactory)
    {
        $this->_categoryFactory = $categoryFactory;
        $this->resultJsonFactory = $jsonFactory;
        $this->productCollectionFactory = $productCollection;
        $this->_obj = $obj;
        $this->categoryCollectionFactory = $categoryCollectionFactory;
        parent::__construct($context);
    }

    public function execute()
    {
        // get parent category
        $categoryId = $this->getRequest()->getParam('category_id');
        $this->getCats($categoryId);
        foreach($this->cats as $cat)
        {
            $this->getProductCollection($cat);
        }
        //$this->getProductCollection($categoryId);
        return $this->resultJsonFactory->create()->setData($this->allProducts);
    }

    public function getCats($categoryId)
    {
        $_category = $this->_categoryFactory->create();

        $category = $_category->load($categoryId);

        //Get category collection
        $collection = $category->getCollection()
                ->addIsActiveFilter()
                ->addOrderField('name')
                ->addIdFilter($category->getChildren());
                $cats = [];
        foreach($collection as $coll)
        {
            $cats[] = $coll['entity_id'];
            $this->cats[] = $coll['entity_id'];
        }
        foreach($cats as $cat)
        {
            $catfactory = $this->_categoryFactory->create();
            $catobj = $catfactory->load($cat);
            if(!$catobj->hasChildren())
            {
                continue;
            }else{
                $this->getCats($cat);
            }
        }
    }

    public function getProductCollection($categoryId)
    {
        $category = $this->_categoryFactory->create()->load($categoryId);
        $collection = $this->productCollectionFactory->create();
        $collection->addAttributeToSelect('*');
        $collection->addCategoryFilter($category);
        // return $collection;
        foreach ($collection as $product)
        {
            $this->allProducts[] = ["name" => $product->getName() , "id" => $product->getId() , "price" => $product->getPrice()];
        }
    }