Scaffold generated Sum of all Integers

Question

This is driving me nuts with loads of undeclared variables. I have created a simple scaffold with text and integers. How to sum up all integers? See image:

enter image description here

I only want to sum up the "Watts". Im using Rails 4; Ruby 2.1.3

I get this: undefined method 'all' for nil:NilClass" when I put this code in my app/models/bathroom_accessory.rb:

def total
 @bathroom_accessory.all.sum(&:watts)
end

Have I done something wrong?

`all` is a class-level method so you can't call it from an instance. — Bart Jedrocha, Feb 12 '15 at 17:08
That's not true. You can absolutely call it. The trouble is what he's calling it on, not where he's calling it from. :) — David Hoelzer, Feb 12 '15 at 17:10

score 1 · Answer 1 · answered Feb 12 '15 at 17:08

1

You've tried to refer to an instance variable rather than the collection of all accessories:

def total
  BathroomAccessory.all.sum(&:watts)
end

answered Feb 12 '15 at 17:08

David Hoelzer

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score 1 · Accepted Answer · answered Feb 12 '15 at 17:49

Another way to do this (without the all):

 def total
   BathroomAccessory.sum(:watts)
 end

For the sake of the question, is important for the OP to understand this call:

@bathroom_accessory.all.sum(&:watts)

Is incorrect since sum is defined at a class level and @bathroom_accessory is declared as an instance variable. Even this code is incorrect:

 def total
   @bathroom_accessory = BathroomAccessory.new
   @bathroom_accessory.sum(:watts)
 end

This last code will raise a NoMethodError error.

Sorry for the delay. Your answer works. Took me time to understand what is going on. — Sylar, Feb 15 '15 at 18:15

Scaffold generated Sum of all Integers

2 Answers2