unable to Update product collection via observer in Magento2

Question

I'm trying to update product collection (excluding some products, to be exact) through observer. I'm using the event catalog_block_product_list_collection Observer is catching the event fine.

in observer execute method:

    public function execute(\Magento\Framework\Event\Observer $observer) {
        $newCollection = $observer->getEvent()
            ->getCollection();
        $newCollection->addAttributeToFilter('entity_id', ['nin' => [1,2,13]]);
        return $this;
    }

but nothing happens.

I've also tried the event catalog_product_collection_load_after but the case is same.

How can i update this collection via observer?

edit: Using addFieldToFilter or addIdFilter results in "main.CRITICAL: illegal state" in log file system.log and no products shows up but overall page loads fine.

Answer 1

I was able to achieve the desired result like this:

$observer->getEvent()
    ->getCollection()
    ->addAttributeToSelect('*')
    ->addAttributeToFilter('entity_id', ['nin' => [1,13,5]]);

and used the event catalog_block_product_list_collection

Answer 2

For this case,you can use addIdFilter(arrayofproductId,true). instead of addAttributeToFilter() at this case.

So in this case, use addIdFilter([1,2,13],true).instead of addAttributeToFilter('entity_id', ['nin' => [1,2,13]]);

That second parameter of addIdFilter() function put the condition nin

See at product collection class Magento\Catalog\Model\ResourceModel\Product\Collection;

 public function addIdFilter($productId, $exclude = false)
    {
        if (empty($productId)) {
            $this->_setIsLoaded(true);
            return $this;
        }
        if (is_array($productId)) {
            if (!empty($productId)) {
              //$exclude flag use for filter collection at nin condition
                if ($exclude) {
                    $condition = ['nin' => $productId];
                } else {
                    $condition = ['in' => $productId];
                }
            } else {
                $condition = '';
            }
        } else {
            if ($exclude) {
                $condition = ['neq' => $productId];
            } else {
                $condition = $productId;
            }
        }
        $this->addFieldToFilter('entity_id', $condition);
        return $this;
    }