proper way of adding custom fields to PS 1.7

[Anonymous No.2]

I have PS 1.7.5.2. What is the proper way of adding custom fields to products, customers etc?

I have created my module and during installation I create new fields by executing some sql:

$sqlInstall="ALTER TABLE " . _DB_PREFIX_ . "product "
        . "ADD ext_id VARCHAR(20) NULL;";

I have added some hooks, for example, hookAdditionalCustomerFormFields. My new field appears in the backend and this is OK. But it does not appear in the api request http://localhost/prestashop/api/products/?schema=blank

until I add a class override

class Product extends ProductCore

..

Overrides seem to be not supported in 1.7, though I can see my new fields via api calls.

My question is: is overriding classes the proper way of adding custom fields and make them appear in the api calls? Or should I do something in my module instead (add some extra hook?) to appear custom fields in the api calls?

 

 

Edited June 17, 2019 by Anonymous No.2
made clearer (see edit history)