Ruby menu calling undefined method

Question

I'm writing my first Ruby on Rails program, which is an application to assist with managing/ organising courses at a university, the students enlisted on them, and the modules belonging to each of the courses.

I currently have two classes: the first, called Application, is the one I am using to interface with the user, looks like this:

class Application
  # To change this template use File | Settings | File Templates.
  require './courseModules.rb'
  def initialize
    mainMenu
  end

=begin
  def navigateTo(what)
    what.new(v).display
    mainMenu
  end  
=end

  def mainMenu
    puts "What would you like to do?
      1: Add module to a scheme
      2: Remove module from a scheme
      3: Query modules
      4: Modify module
      5: Register a student on a scheme
      6: Remove a student from a scheme
      7: Register a student on a module
      8: Remove a student from a module"
case gets.strip
  when "1"
    CourseModules.addModuleToScheme
  when "2"
    CourseModules.removeModuleFromScheme
  when "3"
    navigateTo CourseModules
  when "4"
    navigateTo CourseModules
  when "5"
    navigateTo Student
  when "6"
    navigateTo Student
  when "7"
    navigateTo Student
    end
  end
  Application.new
end

The second, called courseModules is the one I will be using to allow the user to add new courses, and add modules to those courses. This class currently looks like this:

class CourseModules
   # To change this template use File | Settings | File Templates.
   @@moduleScheme = nil
   @@moduleYear = nil
   #@moduleTitle = ""
   @noOfModulesInScheme = 0

   def self.moduleYear
     @@moduleYear
   end

   def initialize(v)
     @val = v
   end

   # Set and get the @val object value
   def set (v)
     @val = v
   end
   def get
     return @val
   end

   def addModule
     moduleName = Module.new(30)
     moduleRefNo = Random(100)
     #moduleTitle = @moduleTitle
     moduleYear(4)

     print "What is the name of the module you would like to add?"
     moduleName = gets
     moduleRefNo
     printf "Which year does the module belong to?"
     @@moduleYear = gets
     puts "#{moduleName}, belonging to #{@@moduleYear} has been added to the system, with reference number #{moduleRefNo}."
     navigateTo Application

   end

   def addModuleToScheme

     # Create an empty hash for the schemes
     schemes = Hash.new()

     # Allow user to enter scheme names into a set of variables, and use each scheme name as a hash/ array of modules.
     # Then allow the user to enter the the modules for each scheme into each of the hashes

     # Create specific hash elements by using the following line:
     schemes = {:scheme1 => scheme1variable, :scheme2 => scheme2variable}

     puts "What is the name of the scheme that you would like to add a module to? "
     schemeName = gets

     # Need to use an if statement here to check whether or not the scheme already exists, if it doesn't, create it, if it does,
     # tell the user that it does.

     if schemes.has_key?(schemeName)
       puts "This scheme has already been added "
     else
       schemes.add(schemeName)
     end

     noOfModulesInScheme + 1
     moduleName.moduleScheme = schemeName
   end

   def removeModuleFromScheme
     moduleName.moduleScheme = nil
   end

   def queryModule

   end

 end

Currently, I'm just working on the first option in the menu- "Add module to scheme". When I try to run the program from my Application.rb class, the menu is displayed, and I enter: "1", which is the option I want to choose.

However, I'm then getting an error saying that my method "addModuleToScheme" is undefined. Could someone point out what I'm doing wrong with my "addModuleToScheme" method?

Many thanks.

Edit 21/08/2012 at 00:35

OK, I think that seems to have solved my addModuleToScheme method, however I'm now getting an error when trying to actually add the scheme name to the hash:

when I select '1' from the menu now, I'm asked for the name of the scheme, however, when I type that in, I get an undefined method error,

undefined method 'add' for {}:Hash (NoMethodError)"

on the line

schemes.add(schemeName)

in my if else statement. Any ideas what I'm doing wrong here?

score 2 · Accepted Answer · answered Aug 20 '12 at 20:09

2

I bet it's telling you that CourseModules.addModuleToScheme is undefined. That is because you have implemented the method as an instance method, when you try to use it as a class method.

Try to either define it as this:

def self.addModuleToScheme
  # ... do stuff
end

or try to use it as an instance method, in which case you'd have to create a new instance of the CourseModules class first.

answered Aug 20 '12 at 20:09

Frost

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...and in case you are a bit confused about the whole class method versus instance method (and class vs. instance variables), I have a longer answer on it here: http://stackoverflow.com/questions/11523547/rails-and-class-variables/11523632#11523632 – Frost Aug 20 '12 at 20:10
Thanks for your reply- that seems to have resolved the original issue: when I select '1' from the menu now, I'm asked for the name of the scheme, however, when I type that in, I get an undefined method error, "undefined method 'add' for {}:Hash (NoMethodError)" on the line "schemes.add(schemeName) in my if else statement. Any ideas what I'm doing wrong here? – Someone2088 Aug 20 '12 at 23:33
You get `undefined method \`add' for {}:Hash (NoMethodError)` because the Hash class doesn't have an `add` method. Try using `schemes[schemeName] = nil` (or some better value) instead. – Frost Aug 21 '12 at 13:30

Ruby menu calling undefined method

1 Answers1