module A
  class B < ActiveRecord::Base
  end
end

require 'active_record'
ActiveRecord::Base.establish_connection(
  adapter: 'postgresql',
  database: 'xxxx',
  host: 'localhost',
  username: 'xxxx',
  password: 'xxxx'
)

module A
  class B < ActiveRecord::Base
    def self.do_something
        A::B.all.each do |record|
          #do something
        end
      end
    end
  end
end

A::B.do_something