Help With id

Hello. I have my rb file:

class CreateDepartamentos < ActiveRecord::Migration   def self.up     create_table :departamentos, :id=>null do |t|       t.string :cvedept, :limit=>10, :null=>false       t.string :desdept, :limit=>20, :null=>false

      t.timestamps     end   end

  def self.down     drop_table :departamentos   end end

but when i try with a new record i get the next error:

Unown columno "departamento.id" in table "departamentos".

but i dont have the field "id" in my table.

Help please!.

you need to tell rails what to use as your primary key (via the set_primary_key function)

Fred