Question

I have the following Rails 3 migration which adds a column game_type to a table called games. It’s supposed to update the value of the game_type depending on whether live is true, but this value never gets saved.

class AddGameTypeToGames < ActiveRecord::Migration

  class Game < ActiveRecord::Base
  end

  def up
    say "Adding game_type column to Games table"
    add_column :games, :game_type, :string, :null => false, :default => 'Demo'

    say_with_time "Migrating live value into game_type column" do
      rows_affected = 0
      Game.all.each do |game|
        if game.live
          game.update_attributes!(:game_type => 'Live')
          rows_affected += 1
        end
      end
      rows_affected
    end
  end
end

I eventually got this to work by changing the line game.update_attributes!(:game_type => 'Live') to Game.connection.execute("UPDATE games SET game_type='Live' where id = #{game.id}").

I’m wondering why update_attributes! wouldn’t work? I have other migrations where this works fine. Including the model is supposed to stop validations getting in the way of the migration. I tried setting attr_accessible :game_type on the Game model in the migration, but this didn’t work.

Answer 1

you have to add this line before running the loop on Game model

Game.reset_column_information
Game.all.each do |game|
  ....
  ....

Sometimes you’ll want to add a column in a migration and populate it immediately after. In that case, you’ll need to make a call to Base#reset_column_information in order to ensure that the model has the latest column data from after the new column was added.

There’s an example of this in the API docs for ActiveRecord::Migration. Look for “Using a model after changing its table”