Product Model With Stock_QTY Scoped to Size - ruby-on-rails

Question

I have a functioning, self built e-com web app, but right now the app assumes we have infinite quantity.
It uses line_items and product models.
I am going to add stock_QTY as an attribute to the product
For items that don't have any variants (sizes, colors etc.), the line_item will be created if and stock_QTY is greater than one.
I'm not sure how to deal with sizes though.
Should I create different Products? IE:
Shirt.create (name:"small green shirt", color:"green", size:S, stock_QTY:4)
Shirt.create (name:"medium green shirt", color:"green", size:M, stock_QTY:6)
Shirt.create (name:"large green shirt", color: "green", size:L, stock_QTY:1)
This seems repetitive, but at least the stock QTY can have some independence. Is there a way to create only one shirt record, with variants, and allow them to have different sizes?
Ideally I'd like
Shirt.create(name:"shirt", colors:['red', 'blue', 'green'], sizes: ['s','m',l'])
and then be able to do
Shirt.where(color => "green").where(size => "L").stock_QTY
=> X number
Shirt.where(color => "green").where(size => "M").stock_QTY
=> Y number
This way I have one model, but it can store different quantities depending on the scope of the variants.
Let me know if this is unclear.
Thanks!
Update
Product.rb
require 'file_size_validator'
class Product < ActiveRecord::Base
has_many :line_items
before_destroy :ensure_not_referenced_by_any_line_item
mount_uploader :image, ImageUploader
validates :price, :numericality => {:greater_than_or_equal_to => 0.01}
validates :title, :uniqueness => true
def to_param
"#{id}_#{permalink}"
end
private
# ensure that there are no line items referencing this product
def ensure_not_referenced_by_any_line_item
if line_items.empty?
return true
else
errors.add(:base, 'Line Items present')
return false
end
end
end
Here is my Product as it is now.
from seeds.rb
Product.create!([
{
:title => "Liaisons Shirt Green",
:description => "",
:has_size => true,
:price => 24.99,
:permalink => "shirt",
:weight => 16.00,
:units => 1.00,
:image => (File.open(File.join(Rails.root, "app/assets/images/dev7logo.png")))
}
])

Answer 1

So, my advice is to improve the DB schema to make it more flexible and scalable ;)
Define the Size and Color models (2 new tables), make your actual Product model the BaseProduct model (just renaming the table) and finally create the Product model (new table) which will have 3 external keys (base_product_id, color_id and size_id) and of course the stock_qty field to define all possible configurations with the minimal repetition of information :)!
Just a little help, you're final classes schema should be like:
class Color < ActiveRecord::Base
end
class Size < ActiveRecord::Base
end
class BaseProduct < ActiveRecord::Base
# This will have almost all fields from your actual Product class
end
class Product < ActiveRecord::Base
# Ternary table between Color, Size and BaseProduct
end
I'm omitting all associations because I like the idea you succeed on your own, but if you need, please just ask :)
This will allows you to do BaseProduct queries like:
base_product.colors
base_product.sizes
product.base_product # retrieve the base_product from a product
and to keep trace of the quantities:
product.stock_qty
product.color
product.size # size and color are unique for a specific product
You can also create some helper method to make the creation process similar to the one you'd like to have (as shown in your question).

Answer 2

Well I understand the approaches you wanted to deal with. Pretty easy business logic if I understand correctly. So you wanted the following things If I get you correctly:
You have so many products
You want to add stock count record
You wanted to validate the product for selling (line items for cart) if the product available
You need to ensure if the product is already in customer's cart when you are deleting that.
So I assumed you already added the stock_qty columns.
Now you need to ensure if the product is available to be added in your cart.
So you need to write your validation in your line_item modem.
class LineItem < ActiveRecord::Base
# other business logics are here
belongs_to :product
before_validation :check_if_product_available
def check_if_product_available
# you will find your product from controller, model should be responsible to perform business
# decision on them.
if !self.try(:product).nil? && self.product.stock_qty < 1
errors.add(:product, 'This product is not available in the stock')
return false
end
end
end
This is the approach I believe is the valid way to do. And moreover, rather saving variants in same product model, I would suggest consider designing your model more efficiently with separate variant model or you can utilize the power of self association.
I hope this will help you. Let me know if I miss anything or miss interpret your problem.
Thanks