Obtaining total for associated columns - ruby

Question

I have 4 models, User, ImageSize, Frame and CartItem. The CartItem model holds all the id's for the 3 prior models, so
class CartItem < ActiveRecord::Base
belongs_to :image_size
belongs_to :user
belongs_to :frame
end
create_table "cart_items", force: :cascade do |t|
t.integer "user_id"
t.integer "image_size_id"
t.integer "frame_id"
end
class User < ActiveRecord::Base
has_many :cart_items
end
My first issue here is this doesn't seem correct, as in my association setup, but for now ill address that another time.
A Frame and ImageSize both have a price column and what I am trying to achieve is to get the sum of the price for Frame and ImageSize for the current user so that Ii can show a subtotal for the user that collects the sum for all cartitems
How can I write this query or collect this data? Here is what I have managed to put together, but surely there's an easier way?
def show
#frame_total = CartItem.frame_price_total(current_or_guest_user)
#image_size_total = CartItem.image_size_price_total(current_or_guest_user)
#subtotal = CartItem.subtotal(#frame_total, #image_size_total)
end
class CartItem < ActiveRecord::Base
def self.frame_price_total(u)
#price_array = []
user = includes(:frame).where(user_id: u)
user.each do |f|
#price_array << f.frame.price
end
#price_array.sum
end
def self.image_size_price_total(u)
#price_array = []
user = includes(:image_size).where(user_id: u)
user.each do |f|
#price_array << f.image_size.price
end
#price_array.sum
end
def self.subtotal(image_size_total, frame_size_total)
total = image_size_total + frame_size_total
BigDecimal.new(total).to_s
end
end

Answer 1

It look good but have N+1 query problem
def show
#user_frames = CartItem.includes(:frame).where(user_id: current_user)
frame_array = []
#user_frames.each do |f|
frame_array << f.frame.price
end
#frame_total = frame_array.sum
end