I’m a Richardson, RU?

If anyone is going along through the Agile Web Development with Rails book and gets to page 66 where you are using the migration “alter table products …” you’ll indubitably come across the error where Rails doesn’t seem to like what you’ve put in the migration file. You may receive an error like:

AddPrice: migrating =====================================================

—add_column(:products, :price, :decimal, {:precision=>8, :default=>0, :scale=>2})

rake aborted!

You have a nil object when you didn’t expect it! You might have 
             \expected an instance of Array. 
             \The error occured while evaluating nil.

(See full trace by running task with—trace)

I found this post which helps out. It looks like the problem is with the decimal type specified so instead of what the book gives, type this as you’re migration and everything should work without a hitch:

class AddPrice < ActiveRecord::Migration
  def self.up
      add_column :products,:price,:integer,:precision => 8,:scale => 2,:default => 0
  end

  def self.down
    remove_column :products, :price
  end
end

So it’s not really a fix and t doesn’t solve the fact that you don’t have a decimal, but at least it will let you move on through the book (and I still can’t figure out why it won’t work, even with rails “on the edge” working)…

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