[Rails] Helper para crear Foreign key en las migraciones de Rails

migration_helper.rb

=begin
 MigrationHelper
 Funciones para la creacion de claves foraneas desde las migraciones
 @author: William Yanez

 Uso: class MyMigration < ActiveRecord::Migration
       extend MigrationHelper
=end

module MigrationHelper
  
  def add_foreign_key(tabla_org,campo,tabla_dest,options=nil)
    constraint_name="fk_#{tabla_org}_#{campo}"
    
    on_update=on_delete="RESTRICT"
    options={} if options.nil?
    on_update=options[:update] if options.has_key?(:update)
    on_delete=options[:delete] if options.has_key?(:delete)
    
    sql =  "ALTER TABLE #{tabla_org} ADD CONSTRAINT #{constraint_name}"
    sql << "FOREIGN KEY (#{campo}) REFERENCES #{tabla_dest}(id)"
    sql << "ON UPDATE #{on_update}  ON DELETE #{on_delete}"
        
    execute sql 
  end  
  
  def drop_foreign_key(tabla_org,campo)
    constraint_name="fk_#{tabla_org}_#{campo}"
    
    #Para PostgreSQL:
    sql="ALTER TABLE #{tabla_org} DROP CONSTRAINT #{constraint_name}"
    
    #Para MySQL:
    #sql="ALTER TABLE #{tabla_org} DROP FOREIGN KEY #{constraint_name}"
        
    execute sql 
  end 
  
end