1.9 - Add product to category collection by ID

Question

I want to add a product to a category page depending on the category ID. This product is not part of the category.

In Mage_Catalog_Block_Product_List I see the following line:

$category = Mage::getModel('catalog/category')->load($this->getCategoryId());

Would it be possible to have an if underneath? - Is this the right place?

$category = Mage::getModel('catalog/category')->load($this->getCategoryId());
if ($this->getCategoryId() == 123) {
  //add product id 456 to the collection
}

If so, how do I add a product to the $category collection?

And further to this, is it possible to insert it in a particular place, lets say inbetween the 3rd and 4th product?

Answer 1

Try Below code fastest way to set product to category

$category = Mage::getModel('catalog/category')->load($this->getCategoryId());
if ($this->getCategoryId() == 123) {
  //add product id 456 to the collection
    $productIds[$product->getId()]  = 1; // here key is product id and value is position 
    $category->setPostedProducts($productIds);
    $category->save();
}