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
>> My first book

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.