How does discord manages roles and permissions in database?

Question

Users can have multiple roles, roles have multiple permissions, and roles are protected by servers. I was wondering do they use relational db for that? Is django capable of doing such thing? Because to fetch each user for server with role will be very expensive. Does discord uses django for this or any other framework? Any thoughts please? I am trying to build a similar schema but I think it will be very expensive for the db transactions and queries.

I have workspace, workspace have users, users have multiple roles, roles have multiple permissions(groups in djangos). And I think this will be very expensive to call a single user to check whether he belongs to this group or not.