Why does my method not work?

In my cinema ruby on rails application I am trying to display the amount of seats that have been booked for a showing in a screen. I have taken code from this question: Count the amount of records are associated to another record

And so have added this code to my screens.rb model:

def remaining_seats
  seats.count - ( bookings || [] ).count
end

def screens_info
  "#{name} (#{remaining_seats}/#{seats.count} remaining)"
end

And display this on the view:

<%= @booking.showing.screen.screens_info %>

But the code in remaining_seats: ( bookings || [] ).count returns 0, so the whole thing will tell me all seats are available.

This is my screen.rb model:

class Screen < ActiveRecord::Base
has_many :seats
has_many :showings
has_many :bookings, through: :showings
def screens_info
    "#{name}"
end

def self.showing_search(showing_id)
    if not showing_id.blank?
        screen = Showing.find(showing_id).screen_id
        self.where("id = ?", screen)
    end
end

def remaining_seats
  seats.count - ( bookings || [] ).count
end

def screens_info
  "#{name} (#{remaining_seats}/#{seats.count} remaining)"
end
end

showing.rb:

class Showing < ActiveRecord::Base
  belongs_to :film
  has_many :bookings
  belongs_to :screen
end

booking.rb:

class Booking < ActiveRecord::Base
  belongs_to :user
  belongs_to :showing
end

And the schema:

create_table "seats", force: :cascade do |t|
t.string "seat"
t.integer  "screen_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end

create_table "showings", force: :cascade do |t|
t.date     "show_date"
t.time     "show_time"
t.integer  "film_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer  "screen_id"
end

create_table "screens", force: :cascade do |t|
t.string   "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end

create_table "bookings", force: :cascade do |t|
t.integer  "user_id"
t.integer  "showing_id"
t.datetime "created_at",     null: false
t.datetime "updated_at",     null: false
t.integer  "seats_quantity"
end

So just to clarify, what I am trying to do is display the amount of seats that are available to be booked for a particular showing in a specific screen - so say a screen has 25 seats and at the 13:00 showing 5 seats have been booked I want to say there are 20 seats remaining.