Rails Observers, Plugins and Migrations are in a race, who wins?

Question

We just added a couple of observers to our Rails application. Now, when running migrations from scratch we get an error saying that a table doesn't exist (duh, we haven't migrated yet). The error is thrown because a plugin in a model is being loaded that asks for column_names.

I am assuming that the observers are causing the models to be loaded because when we comment out the observers line in application.rb, the error is not thrown.

How do I run migrations without loading observers and models?

or

How do I ask for the column_names in my plugin in a way that won't throw an error when running migrations?

Answer 1

I haven't found a decent way to disable Observers at run time. This has been previously discussed in Simple way of turning off observers during rake task?

However, I guess you could "unplug" the plugin code from your model by redefining the troublesome model in your migration:

class YourMigration < ActiveRecord::Migraation
  class YourModel < ActiveRecord::Base; end

  def self.up
    ...
  end

  def self.down
    ...
  end
end

Answer 2

In Rails 3 you can skip adding the observers by determining if Rake is being run:

config.active_record.observers = :my_model_observer unless File.basename($0) == 'rake'

This turns off the observers, which means the models and plugins aren't loaded.

Answer 3

In your model you can catch the specific exception generated when you run migrations.