thewebfellas - ruby on rails development specialists uk

If you have a model that uses validates_acceptance_of, you have an observer for that model and you try to run the migration responsible for creating the underlying table then the db:migrate task will fail. The actual error you receive will depend upon your database engine – on MySQL it looks something like this:

Mysql::Error: Table 'database_name.table_name' doesn't exist: SHOW FIELDS FROM `table_name`

The culprit is changeset 8208 which allows the attribute used by validates_acceptance_of to actually exist in the database rather than being virtual. When running the migration to create the underlying table, environment.rb causes the model observer to be loaded which in turn loads the model itself. When the model is loaded validates_acceptance_of tries to determine the column names of the (as yet non-existent) table and, yes you guessed it, blows up!

The good news is that changeset 8377 was submitted 4 days ago to fix this problem. To take advantage of it you’ll either have to freeze Rails to the latest revision or you can simply apply the patch if you’re using something like Piston to manage vendor/rails.

18th December Update: Rails 2.0.2 has now been released and includes the fix for this problem.

Here’s one that could have you scratching your head in puzzlement for a little while. In Rails 1.2.x you could do something like this in your controller:

class PostsController < ActionController::Base
  before_filter :do_filter
  
  # Controller code
  
  protected
    def do_filter
      # Filter logic goes here
      
      # Halt the filter chain
      false
    end
end

If the filter returned false then processing of the request would stop and you’d see a blank page in your browser.

Not so in Rails 2.0: thanks to changeset 7984 the filter chain is only halted if you render or redirect within your filter. If you really want to get similar behaviour to Rails 1.2.x you could always do this:

def do_filter
  # Filter logic goes here
  
  # Halt the filter chain
  head :bad_request
end

Although you will probably be more popular with your users if you display some kind of friendly error message!

So Rails 2.0 is finished although, thanks to a last minute fix, it’s version 2.0.1 and not 2.0.0 as you might expect.

Ryan Daigle has posted a big list of changes but even that doesn’t catch all of the features in this new version, there are just too many, so we can expect a slew of new books and screencasts soon. Ryan Bates (why are so many Ryans involved in Rails?) is ahead of the game with his excellent Rails 2.0 Railscasts.

I’ve just updated this site without any difficulties and the new project we’ve just started will be built with Rails 2.0 giving us a great opportunity to try out all the new features.

Now we can look forward to the smokin’ fast Ruby 1.9 that should be out soon and then eagerly await the release of Rails 3.0!