On several occasions I’ve had Heroku apps fail to recognize columns I add to the database. The symptoms of this problem are:

• The app throws an error if you visit a page with the new methods referencing the column names
• If you use heroku console and create your new object it won’t have the attributes for your new column.

This happened to me yesterday and here is how to fix it. First, I made sure that the migration had taken effect. I used the handy heroku sql console plugin which allows you to execute sql on your Heroku database. This allowed me to checkout the schema_migrations table and make sure my latest migration was there:

SELECT * FROM schema_migrations;

Then I looked at the table with the added columns to see if it had the changes:

DESCRIBE courses;

The columns were there.

The reset_column_information method turned out to be the key to fixing this problem:

heroku console
>> Course.reset_column_information

Now Course had the recently added attributes. To avoid this problem next time, I’ll use reset_column_information inside of the migration when I change an existing model’s attributes. An additional facet to this solution is that if you access a model class in a migration, you need to open up the class in the migration:

  class Course < ActiveRecord::Base; end

Here are some resources:

• http://rubyquicktips.tumblr.com/post/883943520/model-attributes-not-updating-reset-column-information
• http://jasonpearl.com/?p=13
• http://markmail.org/message/gxmyepl3s55fjknx
• http://niczsoft.com/2010/02/how-to-make-rails-migrations-pretty/