How to use an additional DB

[Mohamed2000]

Hi all.

i need to add a new database connetion to my project, 

for exemple on product detail page, i need to get my product from "prestashop_DB" and the description from "the_external_DB"

(i reash to make a new connection by a new function in "classes/db/Db.php" called "getInstance2" with my parameters, it's like "getInstance", but i don't like it because i must call a new instance before every communication with DB)
who can help me or give me ideas!