Rails - Sep 2007 - create new model - add custom defaults to migration?

I am new to Ruby and Rails, have been messing about with migrations
mostly, was trying to create a migration file that would automattically
add certain columns and triggers to each table in the database, made
some progress with that but now rethinking my approach

when creating a new model/migration file, is it possible to get the
generator to add in default values; in my case I would like a few
columns such as created_on, modified_on, and some triggers to update
these values

so given a model Project, the following migration file is generated via
[i]ruby script/generate model Project[/i]

[code]
class CreateProjects < ActiveRecord::Migration
  def self.up
    create_table :projects do |t|
    end
  end

  def self.down
    drop_table :projects
  end
end
[/code]

but is it possible to have the generated file automatically load in
additional code? i.e.

[code]
class CreateProjects < ActiveRecord::Migration
  def self.up
    create_table :projects do |t|
      t.column :created_on, :datetime
      t.column :modified_on, :datetime
    end

    sql = ''CREATE TRIGGER projects_before_insert BEFORE INSERT ON
projects FOR EACH ROW SET NEW.created_on = NOW(); ''
    execute(sql)

  end

  def self.down
    drop_table :projects
  end
end
[/code]

Thanks in advance for any help or pointers
- J
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ok - after further Google searches came across this great site 
''Railscasts''
''How to Make a Generator'' - http://railscasts.com/episodes/58

armed with a better understanding of how a generator works
I took a look at the model_generator.rb and /templates/migration.rb code

well a quick hack of the /templates/migration.rb code and I am on my way
BUT - this just feels down right dirty hacking this template directly; 
but it is very effective

on windows XP with Ruby in installed at C:\Ruby
the path to this file is
C:\ruby\lib\ruby\gems\1.8\gems\rails-1.2.3\lib\rails_generator\generators\components\model\templates

# the hacked version - created_on, modified_on columns and triggers 
(mysql)
class <%= migration_name %> < ActiveRecord::Migration
  def self.up
    create_table :<%= table_name %> do |t|
<% for attribute in attributes -%>
      t.column :<%= attribute.name %>, :<%= attribute.type %>
<% end -%>
      t.column :created_on, :datetime
      t.column :modified_on, :datetime
    end

    sql = ''CREATE TRIGGER <%= table_name %>_before_insert BEFORE
INSERT
ON <%= table_name %> FOR EACH ROW SET NEW.created_on = NOW(), 
NEW.modified_on = NOW(); ''
    execute(sql)

    sql = ''CREATE TRIGGER <%= table_name %>_before_update BEFORE
UPDATE
ON <%= table_name %> FOR EACH ROW SET NEW.modified_on = NOW(); ''
    execute(sql)
  end

  def self.down
    drop_table :<%= table_name %>
  end
end
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