Rails Migration Question

Can anyone help me in this:

Given the following database migration:

    class DefineDatabase < ActiveRecord::Migration

      def self.up
        create_table "products" do |t|
          t.column "name", :string
          t.column "price_converted", :integer # NOTE: we shouldn't
store monetary values as floats to avoid rounding errors

        create_table "categories" do |t|
          t.column "name", :string

        create_table "categories_products" do |t|
          t.column "product_id", :integer, :null=>false
          t.column "category_id", :integer, :null=>false
          t.column "display_order", :integer, :default=>0, :null=>false

      def self.down
        drop_table "products"
        drop_table "categories"
        drop_table "categories_products"


I need to implement model classes named Category and Product so that the
following code example generates the expected output:

    cat1 = Category.new(:name=>'Books')
    p1 = cat1.products.create(:name=>'My first book', :price=>10.99 )
    puts p1.price_converted # should be the price in cents, that is x
100 and rounded up to next whole number
    >> 1099
    p2 = cat1.products.create(:name=>'My second book', :price=>20.95 )
    puts p2.price_converted
    >> 2095

    cat1.set_display_order(p1, 1) # this should set the 'display_order'
column associated with the product p1 to 1

    prod_array = cat1.products.find(:all, :order=>'display_order,
    puts prod_array[0].name
    >> My second book
    puts prod_array[1].name

instead of just looking for someone that is willing to implement your
models and methods, why don't you just give it a try first and ask if
you encounter any problems?

start by defining the relations between models (has_many,
belongs_to, ...). add callbacks (after_save :convert_price) and
methods (def convert_price). all along write some tests to see if your
code is working correctly.

if you're stuck somewhere, come back and ask for help.