Simple quantity function problems, shopping cart - ruby-on-rails

Question

I just picked up Agile Web Development with Rails 3rd Ed., and I'm going thru the Depot Application chapters, I'm attempting to create a simple Edit quantity function, and delete function. I've had luck with the delete function but no luck with the edit quantity function.
I'm going to provide a lot of information, so please don't feel overwhelmed. I've found this to be a challenging problem.
To add_to_cart.html.erb
<div class="cart-title">Your cart</div>
<table>
<% for item in #cart.items %>
<tr>
<td><% form_for #cart.items, :url => {:action => "cart_update", :id => "#{item.getinventoryid}"} do |f| %>
<%= f.text_field :quantity, :size => '3' %>
<%= f.hidden_field :id, :value => "#{item.getinventoryid}" %>
<%= f.submit 'cart_update' %>
<% end %></td>
<td><%=h item.quantity %> ×</td>
<td><%=h item.title %></li></td>
<td><%=h item.description %></td>
<td class="item-price"><%= number_to_currency(item.price) %></td>
<td><%= link_to 'remove', {:controller => 'inventories', :action => 'remove_cart_item', :id => "#{item.getinventoryid}"} %></td>
</tr>
<% end %>
<tr class="total-line">
<td colspan="4">Total</td>
<td class="total-cell"><%= number_to_currency(#cart.total_price) %></td>
</tr>
</table>
<%= button_to "Checkout", :action => 'checkout' %>
<%= button_to 'Empty cart', :action => 'empty_cart' %>
inventories_controller:
def cart_update
#inventory = Inventory.find(params[:id])
#cart = find_cart
#cart.increment_inventory_quantity(params[:inventory])
end
def remove_cart_item
inventory = Inventory.find(params[:id])
#cart = find_cart
#cart.remove_inventory(inventory)
redirect_to_index("The item was removed")
end
Cart.rb model
attr_accessor :items
def increment_inventory_quantity(id, quantity)
inventory_to_increment = #items.select{|item| item.inventory == inventory}
# We do this because select will return an array
unless product_to_increment.empty?
inventory_to_increment = inventory_to_increment.first
else
# error handling here
end
inventory_to_increment.quantity = quantity
end
def remove_inventory(inventory)
#items.delete_if {|item| item.inventory == inventory }
end
cart_item.rb model
attr_accessor :inventory, :quantity
def getinventoryid
#inventory.id
end
This produces strange results:
Notice the quantity 16 appears in both items from my loop (#Fail). When I submit the form a ArgumentError in InventoriesController#cart_update wrong number of arguments (1 for 2) error is returned. Parameters being passed:
{"commit"=>"cart_update",
"_method"=>"put",
"authenticity_token"=>"sH1tWXTJPltpSq5XaAkww7259IR5ZiflnqSFB2Zb0IY=",
"id"=>"50",
"cart_item"=>{"quantity"=>"16",
"id"=>"50"}}

Answer 1

You are getting the wrong number of arguments error because you are passing one argument to #cart.increment_inventory_quantity in the controller method. That method requires two arguments.
# In your controller:
def cart_update
#inventory = Inventory.find(params[:id])
#cart = find_cart
#cart.increment_inventory_quantity(params[:inventory]) # you are passing one thing
end
# Then in your model:
def increment_inventory_quantity(id, quantity) # the method wants two things
# ...
Possibly you intended to do something like this:
def cart_update
#inventory = Inventory.find(params[:cart_item][:id])
#cart = find_cart
#cart.increment_inventory_quantity(#inventory.id, params[:cart_item][:quantity])
end

Answer 2

Are you sure it's form_for( #cart.items ) and not form_for( item )?