How to monkey patch Commontator::Comment (or any rails engine)? - ruby-on-rails

Question

I just recently learned the term monkey patching, so I'm not sure if I have it right.
I am using the Commontator gem to provide commenting functionality on my Blog (Monologue::Post models) and my other models. I ran into an issue where I was trying to get the parent object from my comment (ie, what was commented on). It looks like I would have to do three joins. Rather than call that in my controller, I thought I could extend the gem's model to have a function comment_parent that would return the parent model.
I have this:
# config/initializers/comment_model_extenders.rb
module Commontator
class Comment < ActiveRecord::Base
def comment_parent
# do some magic
"return parent here"
end
end
end
I must be doing it wrong, because I am getting this error:
irb(main):010:0> c=Commontator::Comment
=> Commontator::Comment(id: integer, creator_type: string, creator_id: integer, editor_type: string, editor_id: integer, thread_id: integer, body: text, deleted_at: datetime, cached_votes_up: integer, cached_votes_down:
integer, created_at: datetime, updated_at: datetime)
irb(main):011:0> c.comment_parent
NoMethodError: undefined method `comment_parent' for #<Class:0xab743d0>
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/dynamic_matchers.rb:26:in `method_missing'
from (irb):11
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:90:in `start'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:9:in `start'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:69:in `console'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands.rb:17:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'
EDIT:
Based off of Fredrick's comments, I changed my code to be
...
def self.comment_parent
...
but the output is as follows:
irb(main):022:0* c=Commontator::Comment
=> Commontator::Comment(id: integer, creator_type: string, creator_id: integer, editor_type: string, editor_id: integer, thread_id: integer, body: text, deleted_at: datetime, cached_votes_up: integer, cached_votes_down:
integer, created_at: datetime, updated_at: datetime)
irb(main):023:0> c.comment_parent
=> "return parent here"
irb(main):024:0> test = c.find(1)
Commontator::Comment Load (35.7ms) SELECT "commontator_comments".* FROM "commontator_comments" WHERE "commontator_comments"."id" = $1 LIMIT 1 [["id", 1]]
=> #<Commontator::Comment id: 1, creator_type: "User", creator_id: 2, editor_type: nil, editor_id: nil, thread_id: 2, body: "Love this parser.", deleted_at: nil, cached_votes_up: 0, cached_votes_down: 0, created_at: "201
5-02-12 22:04:48", updated_at: "2015-02-12 22:04:48">
irb(main):025:0> test.comment_parent
NoMethodError: undefined method `comment_parent' for #<Commontator::Comment:0xad08a10>
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activemodel-4.1.8/lib/active_model/attribute_methods.rb:435:in `method_missing'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/attribute_methods.rb:213:in `method_missing'
from (irb):25
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:90:in `start'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:9:in `start'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:69:in `console'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands.rb:17:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'

Answer 1

Looking at the library, your parent object has_one :thread, :as => :commontable, while the thread has_many :comments.
So, inside a Comment, thread.commontable should get you the other way around back up to your original parent.

Answer 2

Based on the comments, here is my solution:
In general, I wanted it to be called as an instance method, so my original code was correct. I was just calling it wrong. To call an instance method, do one of these:
Model.new.custom_method
or
my_model = Model.new #or .find(n)
my_model.custom_method
For my specific case, I found this solution:
module Commontator
class Comment < ActiveRecord::Base
def comment_parent
# do some magic
thread = Commontator::Thread.find(self.thread_id)
parent_class = thread.commontable_type.camelize.constantize
parent_class.find(thread.commontable_id)
end
end
end