nil：NilClass的未定义方法“ +”

Question

I want to complete a cart part in a site. The first time i add items into the cart it is ok, but the second time with the same items i would get a error:

undefined method `+' for nil:NilClass

Extracted source (around line #19):

current_item = line_items.find_by_product_id(product_id)  
if current_item  
  current_item.quantity += 1  
else  
  current_item = line_items.build(product_id: product_id)  
end  

What is wrong?

Thanks.

Answer 1

The quantity field is probably null in the database. Change the infringing line to something like:

current_item.quantity = current_item.quantity.to_i + 1

Answer 2

nil.to_i returns 0

So use current_item.quantity = current_item.quantity.to_i + 1

Answer 3

Seems like current_item.quantity is nil .

Try to set default value with

...
if current_item
  current_item.quantity ||= 1 # sets to 1 if nil
  current_item.quantity += 1  
else
...

If you store quantity in database, then add to your migration like null: false, default: 1

Hope it helps.