Heroku only: ancestry gem crashes with undefined method `ancestry' for #<Model:0x#######>

I'm seeing an issue on Heroku only with the ancestry gem (cannot reproduce locally): https://github.com/stefankroes/ancestry

A NoMethodError occurred in home#upload: undefined method `ancestry' for #

Method looks like this:

def anthem_upload
    user = User.find_by(id: params[:user_id])
    anthem = Anthem.create!(user_id: user.id, body:params[:post]) <-- HAPPENS HERE
   ...
ene

This method doesn't even call on .ancestry method - but the exception happens as soon as model is created.

Model looks like this:

class Anthem < ActiveRecord::Base
  has_ancestry
 ...
end

Here is the logs:

A NoMethodError occurred in home#anthem_upload:

  undefined method `ancestry' for #<Anthem:0x007f1684d58b98>
  app/controllers/home_controller.rb:335:in `anthem_upload'

Solution

You must run the migration to add the method ancestry to your model:

 heroku run rake db:migrate

Of course assuming your app works at development. If not you can generate the migration with

rails g migration add_ancestry_to_[table] ancestry:string

Taken from ancestry

Edited

After read your comments, I did try my hypothesis. Adding the ancestry gem to a project that doesn't need, and them adding has_ancestry to the model Task, without migrations, at the console I got:

Loading development environment (Rails 4.2.2)
~/ (development) > Task.new
=> #<Task:0x00000008a3d088> {
               :id => nil,
       :project_id => nil,
             :name => nil,
      :description => nil,
    :points_budget => nil,
       :created_at => nil,
       :updated_at => nil
}
~/ (development) > Task.new.save
   (0.2ms)  BEGIN
   (0.2ms)  ROLLBACK
NoMethodError: undefined method `ancestry' for #<Task:0x00000008a9c998>
from /home/alejandro/.rvm/gems/ruby-2.2.2@rails4/gems/activemodel-4.2.2/lib/active_model/attribute_methods.rb:433:in `method_missing'
~/ (development) > Task.new.validate
NoMethodError: undefined method `ancestry' for #<Task:0x00000008ad1210>
from /home/alejandro/.rvm/gems/ruby-2.2.2@rails4/gems/activemodel-4.2.2/lib/active_model/attribute_methods.rb:433:in `method_missing'

The same error you got. Of course, I'm at development. You must try something like this at heroku with: heroku run rails console