Question

I’m writing a course management program in Ruby, to assist with managing courses at a university, the modules associated with each course, and the students registered on each of the courses and modules.

Each student can be registered to only one course (or scheme), and can only take modules that are available on their scheme.

At the moment, I have two classes: Application.rb, which is the class I’m using as the menu, to interact with the user, and CourseModules.rb, which is the class where I’m doing all of the work

Application.rb:

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.add_module
    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

CourseModules.rb:

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


# Attempt at add_module method on 21/08/2012 at 16:30
def self.add_module
  schemes = {}
  scheme_exists = false
  add_another_scheme = true
  add_another_module = true

  while add_another_scheme
    print "Enter scheme name: "
    scheme_name = gets
    @schemes.has_key?(scheme_name.chop) ? scheme_exists = true : scheme_exists = false

    if !scheme_exists
      @schemes[scheme_name.chop] = []
      puts "Scheme #{scheme_name.chop} has been added to the system"
    else
      scheme_exists = false
      puts "This scheme has already been added"
    end

    while add_another_module
      print "Enter module name: "
      module_name = gets
      @schemes[scheme_name.chop].include?(module_name.chop) ? true : @schemes[scheme_name.chop] << module_name.chop
      print "Add another module? "
      ask_if_user_wants_to_add_another_module = gets
      if(!ask_if_user_wants_to_add_another_module.chop == "y" or ask_if_user_wants_to_add_another_module == "yes")
      add_another_scheme = false
    end

 end

 print "Add another scheme? "
 ask_if_user_wants_to_add_another_scheme = gets
 if !(ask_if_user_wants_to_add_another_scheme.chop == "y" or ask_if_user_wants_to_add_another_scheme.chop == "yes")
   add_another_scheme = false
 end
 puts @schemes

end

 while add_another_module
   print "Enter scheme name: "
   scheme_name = gets
   schemes.has_key?(scheme_name.chop) ? scheme_exists = true : scheme_exists = false

   if !scheme_exists
     print "Enter module name: "
     module_name = gets
     schemes[scheme_name.chop] = module_name.chop
     puts "Scheme #{scheme_name.chop} with module #{module_name} has been added to the system"
   else
     scheme_exists = false
     puts "This scheme has already been added"
     puts "Enter module name: "
     module_name = gets
     schemes[scheme_name.chop] = module_name.chop
     puts "Scheme #{scheme_name.chop} with module #{module_name} has been added to the system"
   end

   print "Add another module? "
   ask_if_user_wants_to_add_another_module = gets
   if !(ask_if_user_wants_to_add_another_module.chop == "y" or ask_if_user_wants_to_add_another_module.chop == "yes")
     add_another_module = false
   end
 end
 puts schemes
 end

end

At the moment, when I run the program from Application.rb, the menu is displayed, and I select option 1 (Add module to a scheme).
I’m then asked to enter the scheme name, which I do, and press Enter.

However, I then get an ‘undefined method’ error in ‘add_module’ for ‘has_key’. It says it’s for ‘nil:NilClass (NoMethodError)

Can someone explain this to me? How would I put it right?

Answer 1

You are making reference to @schemes but you define it as schemes = {}, hence the nil:NilClass (NoMethodError).