has_many association migration in Rails

Set up associations in models:

class User < ActiveRecord::Base
  has_many :tasks
end

class Task < ActiveRecord::Base
  belongs_to :user
end

Delete the migration file you've shown.

Add references to tasks table (assuming you already have tasks table):

rails g migration add_references_to_tasks user:references

Migrate the database:

rake db:migrate

---

If you don't have tasks table yet, create one:

rails g migration create_tasks name due_date:datetime user:references # add any columns here

Migrate the database:

rake db:migrate

---

From now on your tasks will have user_id attribute.

Add has_many :tasks to the User model and belongs_to :user to the Task model. In your migration file, delete all the current body of the change method and include a add_index :tasks, :user_id line. After that, run the migration normally.

I know this is an old thread but efforts are only to improve on this. I think what you were going for was to show reference foreign key in the table. In which case:

class addTasksToUser < ActiveRecords::Migration   
   def change
     update_table :users do |t|
     t.references :task
   end   
end

Please make sure your references to the table with the primary key is singular.