Design Technique: How to design a complex system for processing orders, products and units.

Question

Hi,

Programming is fun: I learned that by trying out simple challenges, reading up some books and following some tutorials. I am able to grasp the concepts of writing with OO (I do so in Ruby), and write a bit of code myself. What bugs me though is that I feel I'm re-inventing the wheel: I haven't followed an education or found a book (a free one that is) that explains me the why's instead of the how's, and I've learned from the A-team that it is the plan that makes it come together. So, armed with my nuby Ruby skills, I decided I wanted to program a virtual store. I figured out the following:

My virtual Store will have:

• Products and Services
• Inventories
• Orders and Shipping
• Customers

Now this isn't complex at all. With the help of some cool tools (CMapTools), I drew out some concepts, but quickly enough (thanks to my inferior experience in designing), my design started to bite me. My very first product-line were virtual "laptops". So, I created a class (Ruby):

class Product
  attr_accessor :name, :price
  def initialize(name, price)
    @name = name
    @price = price
  end
end

which can be instantiated by doing (IRb)

x = Product.new("Banana Pro", 250)

Because I want my virtual customers being able to purchase more than one product, or various configurations, I figured out I needed some kind of "Order" mechanism.

class Order

  def initialize(order_no)
    @order_no = order_no
    @line_items = []
  end 

  def add_product(myproduct)
    @line_items << myproduct
  end

  def show_order()
    puts @order_no
    @line_items.each do |x|
     puts x.name.to_s + "\t" + x.price.to_s
    end 
  end
end 

that can be instantiated by doing (IRb)

   z = Order.new(1234)
   z.add_product(x)
   z.show_order

Splendid, I have now a very simple ordering system that allows me to add products to an order. But, here comes my real question.

What if I have three models of my product (economy, business, showoff)? Or have my products be composed out of separate units (bigger screen, nicer keyboard, different OS)? Surely I could make them three separate products, or add complexity to my product class, but I am looking for are best practices to design a flexible product object that can be used in the real world, to facilitate a complex system.

My apologies if my grammar and my spelling are with error, as english is not my first language and I took the time to check as far I could understand and translate properly!

Thank you for your answers, comments and feedback!

Answer 1

One of the cool things I discovered: using integers is one, but translating them into a better currency format, using a string format

puts "%s : $ %.2f" % [@name.to_s, @price]

You can also use the printf, but it looks more C-ish than sparkling Ruby. Also learned that I could make small Units as seperate objects and put these inside an array.

def initialize(name)
  @my_name = name
  @my_stack = []
end

def add_unit(unit)
    if @my_stack.length < 8
        @my_stack << unit
        puts "Added unit"
    else
        puts "Only room for 8 units."
    end

end

Answer 2

More discovery, reading a serious bunch of books which were mind dazzling. But then I remember some memories from last year, where I was doing some nuby web development and the combination of learning some Rails. I thought of CRUD! So, I think all objects need a CRUD interface. I am still wondering if destroying by setting instance variables to nil makes it marked for garbage collection. I use this class to be added inside a balance array. I think using a CRUD approach is the first step to a conventional API.

class Product

    attr_accessor :my_name, :my_description, :my_amount

    # Create
    def initialize(name, description, amount)
        @my_name = name
        @my_description = description
        @my_amount = amount
    end

    # Read/Show
    def show
        x = [@my_name, @my_description, @my_amount] 
    end

    # Update
    def alter(name, description, amount)
        @my_name = name
        @my_description = description
        @my_amount = amount 
    end

    # Destroy
    def clean
        @my_name = nil
        @my_description = nil
        @my_amount = nil
    end

    # Diagnose is Development/Test Mode 
    def diagnose()
     puts "initialize(name, description, amount)"
     puts "{#@my_name} :: {#@my_description} :: {#@my_amount}"
     puts "%s :: %s :: %.2f" % [@my_name, @my_description, @my_amount] 
    end

end