Rails wrong number of arguments (1 for 2) in controller - ruby-on-rails

Question

I'm trying to make a simple calculator that converts farenheit to celsius, using Ruby on Rails. I keep getting the error "Wrong number of arguments (1 for 2)" after I enter some input value. This app has been alot more difficult than it should be. I've been fixing errors as they come up, but can't figure this one out. Other posts I've read are much different and more elaborate than this simple app I'm trying to make. Thanks for any help.
The controller ...
class CalculatorController < ApplicationController
def calculate
#farenheit = params[:temperature]
unless #farenheit.blank?
#farenheit = Temperature.calculate({ :farenheit => #farenheit})
end
#celsius = (#farenheit - 32) * (5.0 / 9.0)
end
private
## Strong Parameters
def user_params
params.require(:farenheit)
end
end
The model...
class Temperature < ActiveRecord::Base
# attr_accessible :farenheit
validates_presence_of :farenheit
validates_numericality_of :farenheit
end
The view...
<h1>Temperature Calculator</h1>
<%= form_tag(calculator_calculate_path, method: "get", action: "calculate") do |form|%>
<p>Please enter a temperature in degrees Farenheit</p>
<%= text_field_tag 'temperature', #farenheit %></p>
<%= submit_tag 'Convert' %>
<h2>Result: </h2>
<h3> <% #celsius %> </h3>
<% end %>
The stack trace (first 10 lines)...
activerecord (4.1.6) lib/active_record/relation/calculations.rb:109:in `calculate'
C:in `calculate'
app/controllers/calculator_controller.rb:6:in `calculate'
actionpack (4.1.6) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.1.6) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.1.6) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'

Answer 1

You've defined an instance method calculate in your CalculatorController, but calculate is also a class method defined in ActiveRecord. It is the ActiveRecord class method that you are calling when you say
#farenheit = Temperature.calculate({ :farenheit => #farenheit})
and that method requires at least two arguments. Here are the docs:
calculate(operation, column_name, options = {}) public
This calculates aggregate values in the given column. Methods for
count, sum, average, minimum, and maximum have been added as
shortcuts. Options such as :conditions, :order, :group, :having, and
:joins can be passed to customize the query.
See http://apidock.com/rails/ActiveRecord/Calculations/ClassMethods/calculate
I'm not sure why you're using the calculate class method though. Why not use only your calculation of #celcius? The following should get your calculate method working without an ArgumentError:
def calculate
#farenheit = params[:temperature]
unless #farenheit.blank?
#celsius = (#farenheit.to_i - 32) * (5.0 / 9.0)
end
end