Rails：nil:NilClass 的未定义方法“*”

Question

I am newbie to rails and want to do basic maths in model to get selling price from some maths. I am writing a simple equation in product model. Here is it:

 def selling_price
  foodio_price + (foodio_price*@@tax) + @@dc
 end

But it is giving error- undefined method `*' for nil:NilClass. It is not recognizing * for multiplication as well as + for sum. Can anybody tell what's wrong here?

Answer 1

One of your variables in that function (like foodio_price or @@tax ) is nil . Everything in Ruby is an object, even including nil , which you may know in other programming languages as null . Every instance of nil inherits from the class NilClass . Hence, nil:NilClass is referring to an instance of nil which is of type NilClass .

To debug this issue you can check which (or al three) of these values is nil by adding puts statements.

---

My guess is that both @@tax and @@dc are nil . Rarely do you need to use these class variables in Rails. I'd suggest just declaring the tax and dc as constants, so something like

TAX = 0.09 DC = 0.10

somewhere in your class file.

---

For default values on a nil parameter for foodio_price

def selling_price foodio_price if foodio_price.nil? return 0.0 foodio_price + (foodio_price*@@tax) + @@dc end

Answer 2

The error is saying the foodio_price is an object from NilClass class

In pseudo code, foodio_price = nil

Your variable foodio_price is not instancied (don't have any value yet)

You should try this

def selling_price(foodio_price)
  foodio_price + (foodio_price*@@tax) + @@dc
end

And in other places of your code, where you call the function selling_price , you pass it the parameter foodio_price

Answer 3

it worked. Changed my model to:

 def selling_price
  self.foodio_price  ||= 0.0  
  foodio_price + (foodio_price*@@tax) + @@dc
 end

Answer 4

foodio_price + ((foodio_price || 1)*(@@tax || 1|) + (@@dc || 0)

试试这个