Ruby on Rails Order By Using Associations

I currently have an order by working on my Ruby on Rails application so that on the Bookings index a user can order their bookings by show_date. This is done through the following in the bookings_controller:

def index
   @bookings = Booking.joins(:showing).all.order(params.fetch(:sort, 'id asc'))
end

And the view code:

<form>
    Order by:
    <select name="sort">
        <option value="show_date ASC">Show Date (Oldest First)</option>
        <option value="show_date DESC">Show Date (Most Recent First)</option>
    </select>
    <button>
        Go
    </button>
</form>

But what I want to do is enable the user to order by the film's title as well as the show date. I have tried to do this with this code:

views/bookings/index.html.erb:

<form>
    Order by:
    <select name="sort">
        <option value="show_date ASC">Show Date (Oldest First)</option>
        <option value="show_date DESC">Show Date (Most Recent First)</option>
        <option value="title ASC">Film Title (A-Z)</option>
        <option value="title DESC">Film Title (Z-A)</option>
    </select>
    <button>
        Go
    </button>
</form>

And the bookings_controller:

def index
   @bookings = Booking.joins(:showing, :film).all.order(params.fetch(:sort, 'id asc'))
end

But this doesn't work and I get the error:

ActiveRecord::StatementInvalid in Bookings#index 

SQLite3::SQLException: no such column: film: 
 SELECT "bookings".* FROM "bookings" INNER JOIN "showings" ON 
 "showings"."id" = "bookings"."showing_id"  ORDER BY film ASC

I think it is because their isn't an association between bookings and film.

Booking.rb:

belongs_to :user
belongs_to :showing
delegate :screen, to: :showing

Showing.rb:

belongs_to :film
has_many :bookings
belongs_to :screen

Film.rb:

has_many :showings
belongs_to :certificate
belongs_to :category