Using mapped function

self.env[].search([]).mapped('field_name')

Hello, Othmane Lafjer

I hope you are doing well.

- You can use the .mapped() function to get many fields's value (here, site_id) in list.

Example,
You can use .mapped() like this:

sites = self.env[model].search([]).mapped(field)

FYI:
model = Model that field is present in.
field = Which field's value you want to get in list.

I hope this will help you.

Thanks & Regards,
Email: odoo@aktivsoftware.com
Skype: kalpeshmaheshwari

why dont you use the search_read instead?