How to reflect in the database a new belongs_to and has_many relationship in Ruby on Rails

I am new to rails (usually a python guy) and have just been trying to build a simple task manager application for fun. I am using Devise for authentication and have a single Task object I am trying to relate to a user. I have added the following to the Task model:

class Task < ActiveRecord::Base
    belongs_to :user
end

and I have added the following in my User model for Devise:

class User < ActiveRecord::Base
   has_many :tasks

   <<normal Devise stuff>>
end

Whenever I added this information I then ran: rake db:migrate. It then gave me an error that the database field did not exist for user_id when I tried to do anything with it.

I am sure it is something rather simple that I am missing. Thanks for the help.