migrations_sample.rb

class CreateProductPreferences < ActiveRecord::Migration
  def self.up
    create_table :product_preferences, :force => true do |t|
      t.integer :user_id
      t.integer :product_id
      t.float  :preference
      t.timestamps
    end
  end

  def self.down
    drop_table :product_preferences
  end
end

class AddIndexToProductPreferences < ActiveRecord::Migration
  def self.up
    remove_column :product_preferences, :id
    change_column :product_preferences, :user_id, :integer, :limit => 8, :null => false
    change_column :product_preferences, :product_id, :integer, :limit => 8, :null => false
    change_column :product_preferences, :preference, :float, :null => false
    add_index :product_preferences, :user_id
    add_index :product_preferences, :product_id
    execute("ALTER TABLE product_preferences ADD PRIMARY KEY user_id")
    execute("ALTER TABLE product_preferences ADD PRIMARY KEY product_id")
  end

  def self.down
    add_column :product_preferences, :id
    add_index :product_preferences, :id
    change_column :product_preferences, :user_id, :integer
    change_column :product_preferences, :product_id, :integer
    change_column :product_preferences, :preference, :float
    remove_index :product_preferences, :user_id
    remove_index :product_preferences, :product_id
    execute("ALTER TABLE product_preferences REMOVE PRIMARY KEY user_id")
    execute("ALTER TABLE product_preferences REMOVE PRIMARY KEY product_id")
    execute("ALTER TABLE product_preferences ADD PRIMARY KEY id")
  end
end