rails add subcategory migration code example

Example 1: rails g migration add columns

$ rails generate migration AddDetailsToProducts part_number:string price:decimal

Example 2: rails migration populate data

class AddSystemSettings < ActiveRecord::Migration
 	def change
      create_table :system_settings do |t|
        t.string  :name       
        t.integer  :position
      end

      # populate the table
      SystemSetting.create :name => "notice"
    end
  end