Question

I’m running the following method and I’m successfully passing two arguments (inventory, quantity) into the method. However I’m incorrectly using .first and .each methods. I’m attempting to replace .each with the .select to select for the cart item with the Inventory id: 6

possible .each replacement: (does not function) inventory_to_increment = @items.select{|item| item_id == inventory}

def increment_inventory_quantity(inventory, quantity)
   inventory_to_increment = @items.each{|item| item.inventory == inventory}
   unless inventory_to_increment.empty?
      inventory_to_increment = inventory_to_increment.first
   else
      # error handling here
   end
   inventory_to_increment.quantity = quantity.to_i
end

I’ve used Ruby Debugger, to debug my code:

inventory_to_increment = @items.each{|item| item.inventory == inventory}

p inventory = 6

unless inventory_to_increment.empty?

CartItem:0x102c4a4c0 @quantity=22, @inventory=#<Inventory id: 1

CartItem:0x102c49638 @quantity=2, @inventory=#<Inventory id: 8

CartItem:0x102c48918 @quantity=4, @inventory=#<Inventory id: 50

CartItem:0x102c47b80 @quantity=2, @inventory=#<Inventory id: 6

inventory_to_increment.first

CartItem:0x102c4a4c0 @quantity=22, @inventory=#<Inventory id: 1 

inventory_to_increment.quantity = quantity.to_i

= 3

I’ve tried several combinations and I need some basic Ruby array guidance. Thank you in advance!

UPDATE OUTPUT FOR ANSWER

inventory_to_increment = @items.select{|item| item.inventory_id == inventory}
(rdb:1) list
[21, 30] in /Users/justin/cart/app/models/cart.rb
   21   
   22  
   23  def increment_inventory_quantity(inventory, quantity)
   24  debugger
   25  
=> 26     inventory_to_increment = @items.select{|item| item.inventory_id == inventory}
   27   unless inventory_to_increment.empty?
   28       inventory_to_increment.first
   29   end
   30  
(rdb:1) p @items
[#<CartItem:0x102df1828 @quantity=22, @inventory=#<Inventory id: 1>>, #<CartItem:0x102df09a0 @quantity=2, @inventory=#<Inventory id: 8>>, #<CartItem:0x102ded908 @quantity=21, @inventory=#<Inventory id: 50>>]
(rdb:1) p inventory
50
(rdb:1) p quantity
"11"
(rdb:1) p item.inventory.id
NameError Exception: undefined local variable or method `item' for #<Cart:0x102df18f0>
(rdb:1) p item.inventory_id
NameError Exception: undefined local variable or method `item' for #<Cart:0x102df18f0>
(rdb:1) next
/Users/justin/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/rescue.rb:162
rescue_action(exception)

Answer 1

It seems Inventory is an object and if so it’s likely that your item.inventory == inventory will not work as expected. Let’s say you have an Item class.

class Item
    attr_accessor :inventory_id, :quantity

  def initialize(inventory_id, quantity)
    @inventory_id = inventory_id
    @quantity = quantity
  end
end

and then you create two objects and compare them:

>> item1=Item.new(8,2)
=> #<Item:0xb7b733bc @inventory_id=8, @quantity=2>
>> item2=Item.new(8,2)
=> #<Item:0xb7b6b7c0 @inventory_id=8, @quantity=2>
>> item1==item2
=> false

This is because you will compare the object ids (0xb7b733bc to 0xb7b6b7c0) instead of the content of the objects.

>> item1.inventory_id==item2.inventory_id
=> true

It then seems you only want to add to the quantity to the first item matching the inventory id. If that is correct then you can try something like this

 inventory_to_increment=items.select {|item| item.inventory.inventory_id==inventory}
 unless inventory_to_increment.empty?
    inventory_to_increment.first.quantity+=quantity
 end