From: Brian Tickler <btickler@...>
Date: 2009-09-20T04:18:26+09:00
Subject: Re: Getting to one attribute of my marshalled array of objects

Thanks Doug,

I implemented all those changes.  I guess I just went too far down the 
wrong road with trying to handle the empty inventory, so I removed that 
whole mechanic.  Part of that was that I tried to marshal @carArray 
originally but messed it up somehow (it only dumped the object ID or 
something), and that's when I tried to marshal self instead and it 
worked.  Not sure what I did there since when I tried again with 
@carArray it worked fine.

I am having another issue, though.  In order to delete a car, I need to 
number the inventory when it displays so that I can ask the user to tell 
me which car to delete by its number on the list (this is part of the 
assignment so I can't really do it another way).

At first I thought I would modify the to_s on CarInventory which right 
now just iterates through the array of Cars using .each and calls 
Cars.to_s, but then I decided it would be more robust if Cars.to_s was 
aware of whether it was being called repeatedly as part of a listing or 
not, from anywhere.

So I added a parameter "def to_s(listPosition=0)" to Car.to_s and 
changed the .each call in the CarInventory.to_s to pass a position 
number.  When I run the progrma now though I get a really bizarre 
behavior...I was supposed to get this type of output with 2 cars in my 
data file (simplified because I am also formatting it to comform to 
columns, etc.):

[1] VIN# Year Make Model Color Price
[2] ...

Instead I got the same results without any bracketed list numbers...so I 
added a debug counter and a puts of the relevent part of my string 
output, and I got this:

Called 1 times
[1]
Called 2 times
[2]
Called 3 times
nil
VIN# [...]
Called 4 times
nil
VIN# [...]

Which is where I am stuck...after adding the parameter Ruby appears to 
be calling to_s 4 times now instead of 2 times and I have no idea why. 
The first 2 times it gets the first part of the string I am building set 
up correctly, but loses everything else and the second 2 times it does 
the whole rest of the string build correctly but ignores the first part. 
I have tried everything I cna thinnk of to display the strings invloved 
at every stage/state and it seems ok...I just can't figure out why the 
to_s is calling four times when it should be twice.

Source below (you can run it, add a car or two, then uncomment the DEBUG 
lines to see what happens):

----SOURCE

class Car

  # DEBUG: @@debugCounter = 0

  def initialize(vin, year, make, model, color, price)
    @vin = vin
    @year = year
    @make = make
    @model = model
    @color = color
    @price = price
  end

  def to_s(listPosition=0) # allow for a listing position to be passed
    # DEBUG: @@debugCounter = @@debugCounter + 1
    # DEBUG: puts "Called #@@debugCounter times"
    displayString = ""
    80.times {displayString << " "} # lay down a canvas of spaces to 
build the full displayString
    if !self.vin
      displayVIN = "(No VIN)"
    else
      displayVIN = self.vin
    end
    if !self.color
      displayColor = ""
    else
      displayColor = "(#@color)"
    end
    # DEBUG: debugString = "[" + listPosition.to_s + "]" if listPosition 
!= 0
    # DEBUG: puts debugString
    displayString[0, 0] = "[" + listPosition.to_s + "]" if listPosition 
!= 0
    displayString[6, 0] = displayVIN
    displayString[25, 0] = @year + " " + @make + " " + @model + " " + 
displayColor
    displayString[70, 0] = @price
    displayString = displayString.strip # make the format look like a 
"normal" to_s call if passed no list position
  end

  def <=> (compare)
    self.year  <=> compare.year
  end

  attr_accessor :vin, :year, :make, :model, :color, :price

end

class CarInventory

  @@inventoryFile = "cars.data"

  def initialize
    if File.exists?(@@inventoryFile)
      File.open(@@inventoryFile) do |file|
        @carArray = Marshal.load(file)
      end
    else
        @carArray = Array.new
    end
  end

  def save
    File.open(@@inventoryFile, "w+") do |file|
      Marshal.dump(@carArray, file)
    end
  end

  def addCar(car)
    @carArray << car
  end

  def updateCar(car)
    updateIndex = @carArray.index(car)
    if updateIndex
      @carArray[updateIndex]  = car
    else
      puts "Cannot find car #car.vin\n"
    end
  end

  def delCar(car)
    @carArray.delete(car)
  end

  def to_s
    if @carArray.first
      @carArray.each {|car| car.to_s(@carArray.index(car) + 1)}
    else
      return "(No inventory)"
    end
  end

  def ==(compare)
    self.vin == compare.vin
  end

  def sort(sortBy)
    case sortBy
      when "V":
      when "M":
      when "P":
      when "Y":
    else
    end
  end

  def filter(filterArray)

  end

attr_reader :carArray, :inventoryFile

end

puts "Car Inventory 1.0 - Brian Tickler\n"

cars = CarInventory.new

loop do
  puts "\n#     VIN                 Car Description 
Price\n"
  puts 
"----------------------------------------------------------------------------\n"
  puts cars.to_s
  puts 
"----------------------------------------------------------------------------\n"
  puts "(A)dd a new car\n"
  puts "(E)dit a car\n"
  puts "(D)elete a car\n"
  puts "(S)ave changes\n"
  puts "(Q)uit\n"
  puts "\nCommand: "
  command = gets.chomp.upcase
  case
    when command =~ /^A/ :
      puts "\nAdd a new car:\n"
      puts "\nVIN:"
      vin = gets.chomp
      puts "\nYear:"
      year = gets.chomp
      puts "\nMake:"
      make = gets.chomp
      puts "\nModel:"
      model = gets.chomp
      puts "\nColor:"
      color = gets.chomp
      puts "\nPrice:"
      price = gets.chomp
      newCar = Car.new(vin, year, make, model, color, price)
      cars.addCar(newCar)
    when command =~ /^E/ :
      puts "\nEdit a car:\n"
    when command =~ /^D/ :
      puts "\nDelete a car:\n"
    when command =~ /^S/ :
      cars.save
      puts "\nSaved to #cars.inventoryFile\n"
    when command =~ /^Q/ :
      puts "Are you sure? [Y/N]"
      confirm = gets.chomp.upcase
      exit if confirm =~ /^Y/
      next
    else puts "Illegal Command: #{command}"
  end
end


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