[Heroku] Access Rails's model in migration, heroku rake db:migrate, uninitialized constant

I wanted to use Rails's migration to add new column to a table and fill this column with default value.

add_column :students, :student_id, :integer 

Student.all.each { |s| s.update_attributes!(:student_id => s.id+10000) }

I run this locally.

rake db:migrate

It worked without any problem.

Then I deployed to Heroku and run;

heroku rake db:migrate

I found this error.

 uninitialized constant AddStudentIdToStudents::Student

After googling for a while, I found this blog post Heroku Migration Fails to Update Attributes: reset_column_information

The way to solve this issue(don't know why) is to open up the class inside migration file like this;

class AddStudentIdToStudents < ActiveRecord::Migration

  class Student < ActiveRecord::Base; end

  def change

    add_column :students, :student_id, :integer

    Student.all.each { |s| s.update_attributes!(:student_id => s.id+10000) }

  end

end

This works for me.

Note: Rails 3.1.0