Rails polymorphic links and joins?

Question

Ruby on Rails

Hello. Postgresql database How to correctly join a table with a polymorphic field. For example, I need to display a value from a particular table in the organization field, depending on the polymorphic relationship. I am doing at the DB level, are there any other options. Thanks?

class User < ApplicationRecord
  belongs_to :userable, polymorphic: true, optional: true
  belongs_to :supplier, foreign_key: :userable_id, optional: true
  belongs_to :institution, foreign_key: :userable_id, optional: true
end

    @users = User
      .left_outer_joins( :institution, :supplier )
      .select( :username, 
               " CASE users.userable_type WHEN 'Institution' THEN institutions.name WHEN 'Supplier' then suppliers.name else '' END AS organization"
      )
      .order( :username )