CODEWITHSUNDEEP
ruby-on-railsrails-migrations
TheIrishGuy
TheIrishGuy

Reputation: 2573

Migration critique

Working on a 3.0 rails project for a client and I have a sensitive migration that I need to run off a live production server. Its essentially suppose to down case all the State abbreviations in the DB, FL -> fl, PA -> pa etc... I can't test locally due to restrictions: does calling the wording of the migration effect anything? I know it does with add and create etc but not sure when updating info like this.

rails g migration UpdateStateAbbreviation

def self.up       
  say_with_time "Updating states abbreviation..." do
  State.find(:all).each do |s|
    tmp = s.abbreviation.downcase
    s.update_attribute :abbreviation, tmp
  end
end end

Rake db:migrate

Upvotes: 1

Views: 50

Answers (1)

tadman
tadman

Reputation: 211560

One very important rule with migrations is to never reference models in your migrations. This might seem like an academic concern, but at some point in the future you may not have a State model at all, and when you remove app/models/state.rb then this migration will not work.

A properly constructed migration will execute properly regardless of changes in the future. Whatever it does may be later un-done, there's nothing wrong with that, but setting it up for failure is never a good idea.

You can do this downcasing operation in your database using a string function and something like:

execute "UPDATE states SET abbreviation=LOWER(abbreviation)"

Using models in the migration causes all sorts of problems. This goes for using your model to pre-populate certain key records as well. Use seeds.rb if you must, or even better, a rake task to do it for you.

As a note, if you can't test locally you have a very flawed development process. You should always run and test your migrations, both up and down where applicable, to ensure that they work correctly. Where you can't get actual production data for reasons of security or privacy, work with your DBA to get a scrubbed, non-sensitive version for testing purposes. State names should not be confidential, for instance.

Upvotes: 2

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