Assiging product to categories

Question

I'm trying to assign a product to a number of categories programmatically. I'm using this code to do so :

$arrayofCategories = array($Id1,$Id2);
$product->setCategoryIds($arrayofCategories);

Note that i'm using that same $product to set others attributes and they were set properly but when i check the product in backend in its categories section, none of the categories with the ids in the array is checked.

Is this the right syntax ?

Answer 1

Yes it seems to be the right syntax, but keep in mind that if you don't merge new IDs with olders it override the olders one.
Take a look at this answer it may help you : https://stackoverflow.com/a/6512286/3531064