Handling multiple carts in rails - ruby-on-rails

Question

I'm wondering if there is a shorter solution for my problem.
I'm currently building a multiple shop system, which means a website with different shops where you have 1 open cart for each shop.
This cart can be owned from a guest or a user.
The cart/order should only be created when an item is added.
The following definition is placed in the application controller.
def find_order_by_shop(shop)
shop = Shop.find(shop.to_i) if !(shop.class == Shop)
if session["order_id_for_shop_#{shop.try(:id)}"]
order = Order.find_by_id_and_state(session["order_id_for_shop_#{shop.id}"],'open')
if order
if current_user
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => session["order_id_for_shop_#{shop.id}"]).delete_all
order.update_attribute(:user_id, current_user.id)
order = current_user.orders.where(:shop_id => shop.id , :state => 'open').first
if order
# delete all exept first
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => order.id).delete_all
else
# create new
order = current_user.orders.new(:shop_id => shop.id , :state => 'open')
end
end
else
order = Order.new(:shop_id => shop.id, :state => 'open')
end
else
if current_user
order = current_user.orders.where(:shop_id => shop.id , :state => 'open').first
if order
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => order.id).delete_all
else
order = current_user.orders.new(:shop_id => shop.id , :state => 'open')
end
else
# guest
order = Order.new(:shop_id => shop.id , :state => 'open')
end
end
session["order_id_for_shop_#{shop.try(:id)}"] = order.id
return order
end
Updating the session while adding an item to the cart/order
...
def create # add item to order
#order = find_order_by_shop(params[:shop_id].to_i)
#order.save # save cart
session["order_id_for_shop_#{params[:shop_id]}"] = #order.id
...
This doesn't seem to be the correct rails way.
Any suggestions ?

Answer 1

I don't know about 'shorter', but just glancing at your code I would make a few recommendations.
Each change you make, test the code. Hopefully you have unit and functional tests, if not then check expected behaviour in a browser.
Try to split your logic into sensible, small, tight units with sensible names. Turn them into methods. As you do so, you may find some problems or points where you could optimise. For example:
if order
if current_user
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => session["order_id_for_shop_#{shop.id}"]).delete_all
order.update_attribute(:user_id, current_user.id)
order = current_user.orders.where(:shop_id => shop.id , :state => 'open').first
if order
# delete all exept first
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => order.id).delete_all
else
# create new
order = current_user.orders.new(:shop_id => shop.id , :state => 'open')
end
end
else
order = Order.new(:shop_id => shop.id, :state => 'open')
end
As there's an 'if order' conditional around this whole block, the internal 'if order' is redundant and the whole 'else' branch can be removed:
if order
if current_user
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => session["order_id_for_shop_#{shop.id}"]).delete_all
order.update_attribute(:user_id, current_user.id)
order = current_user.orders.where(:shop_id => shop.id , :state => 'open').first
# delete all except first
current_user.orders.where(:shop_id => shop.id , :state => 'open').where.not(:id => order.id).delete_all
end
else
order = Order.new(:shop_id => shop.id, :state => 'open')
end
Now you can split the functionality up into small, reusable blocks:
def order_from_shop(shop_id)
Order.new(:shop_id => shop_id, :state => 'open')
end
Look through your code and you can see at least two places that you can use this method.
Notice that there is no return statement. The Ruby/Rails 'way' is to allow the automatic return to kick in - the result of the last statement in a method is returned without explicitly declaring it. You can apply this to the end of your main method:
...
session["order_id_for_shop_#{shop.try(:id)}"] = order.id
order
end
Back to the rest of the code, start extracting more methods, like:
def user_order_from_shop(shop_id)
current_user.orders.where(:shop_id => shop.id , :state => 'open').first
end
There's a few places you can use that, too.
Encapsulate your if statements in small methods, of the form:
def method
if xxx
a_method
else
a_different_method
end
end
According to Sandi Metz, no method should have more than 5 lines. You don't have to be that extreme but it's useful to do so.
Eventually you'll have something that reads a lot more like English, so will be much easier to read and to determine the behaviour of at a glace. At that point you may well notice a lot more duplication or unnecessary, dead chunks of unreachable code. Be ruthless with both.
Finally, this whole thing looks like it needs its own class.
# app/services/shop_order_query.rb
class ShopOrderQuery
attr_accessor :shop, :order, :current_user
def initialize(shop, order, current_user)
self.shop = shop
self.order = order
self.current_user = current_user
end
def find_order_by_shop
...
...
end
private
# support methods for main look-up
def order_from_shop(shop_id)
...
end
...
...
end
Then call it with
ShopOrderQuery.new(shop, order, current_user).find_order_by_shop
Then it's all nicely tucked away, and usable from wherever you can pass it a shop, order and current user... And it's not cluttering up your controller.
For further reading, look for blog posts on making thin controllers, extracting service objects and Sandi Metz's Rules. Also, buy Sandi's book on Ruby OO programming.