Symfony service registeration error

[Hessam]

When i go to the page that loads my symfony service , it tells me there is no such a service with this name registered.

my config.yml file looks like this:

services:
  product_repository:
    class: Foo\Repository\ProductRepository
    arguments: ['@doctrine.dbal.default_connection', '%database_prefix%']

and my module structure is like the attached image. (this is the tutorial module)

What is really wrong?

Edited September 17, 2018 by Hessam (see edit history)