How to add data to a newly created column in migration?

In an already-deployed application, in my seeds.rb, I have the following:

State.create!(:state => "Alabama")
State.create!(:state => "Delaware")
...

Now I wanted to add the two-letter code for each state.

So I made a migration like this:

class AddStateCodeToStates < ActiveRecord::Migration
  def self.up
    add_column :states, :state_code, :string

    update(<<-SQL
    UPDATE states SET state_code='WA' where state = 'Washington'
    SQL
    )
    ...lots of these SQL statement...
  end

  def self.down
  end
end

Problem is:

In development environment, when I want to recreate the database from scratch, then after the migrations run, at that point the seeds.rb has not yet been run.

So, the UPDATE xxx in the AddStateCodeToStates migration has no data to work with (sta开发者_开发知识库tes table is empty because the data will be populated from the seeds.rb), thus the state_code remains NULL.

So my questions are (they are so related, so sorry for not asking them as each separate question):

1. How do I populate the state_codes when recreating the database (after the states table has data in it)?
2. How do I get the state_codes when rake db:migrate on the deployed app (seeds.rb does not run on rake db:migrate)
3. Should I not have used seeds.rb in the first place (and instead put data into the migrations)?

Like many things in Rails, you have many options, but.... general practice is to put necessary application data in seeds.rb. You should write seeds.rb in a way that it can be run multiple times without adding extra records, e.g.

State.find_or_create_by_state(:state => 'state_name_here', ':state_code => 'code here')