Question

i use a simple PHP framework (like Codeigniter) without ORM.

I have a database with product data (prices, sells, page in catalog…).

And i want to calculate the conversion per page and the conversion per product.

The calculations with SQL are not a problem, but i don’t really know where to put them in.

Should I create a “Page” and a “Products” model with methods like
"Page::getConversions($page_id)" or a "ConversionPerPage" and a "ConversionPerProduct" model, or sth. completely other.

Answer 1

I think that the best model classes are to have two classes for each table – one for object and plural for static classes.
For example: if you have Page table then you should have Page and Pages classes.
First one will allow you to have one object from table and you can do the regular methods on it like:

$page = new Page($page_id);
$conversions = $page->getConversions();
$page_number = $page->getNumberInBook(); etc

On the other hand in Pages class you can put the methods that will (usually) return the array of Page and those methods will usually be static:

$pages = Pages::getPagesByCatalog($catalog_id);

This way you will have real OOP and code complete with full model MVC implementation.
I hope that this model hierarchy will help you. We are using it in our office and it showed to be really good.
All the best!