NoMethodError on Mongoid method call

Question

I am calling a class method of another model in my model and it seems to not find it.

Details

add_existing_items is the instance method of Category from where I make a call to class method of Metadata and this fails with the error.

Caught exception : NoMethodError : undefined method `update_or_add_metadata' for Mongoid::Relations::Metadata:Class
/Users/anil20787/workspace/repos/anil_reps/metadata_favorite/app/models/category.rb:36:in `block in add_existing_items'

This call to class method of Metadata works absolutely fine when I call it from my Category controller.

Category model:

class Category
  include Mongoid::Document

  belongs_to :catalog
  has_many :category_items

  # fields go here

  # validations go here

  def add_existing_items(inputs)
    if inputs[:category_item_ids] && inputs[:category_item_ids].kind_of?(Array)
      inputs[:category_item_ids].each do |category_item_id|
        category_item = CategoryItem.find(category_item_id)
        new_item = category_item.dup
        new_item.category = self
        new_item.save!
        # 'new_item' document gets saved successfully
        # But the below call to class method of another class fails! Why?
        Metadata.update_or_add_metadata(new_item, true)
      end
    end
  end
end

Metadata model:

class Metadata
  include Mongoid::Document
  include Mongoid::Timestamps

  # fields go here
  # validations go here
  belongs_to :outlet

  # instance methods go here

  class << self
    def update_or_add_metadata(item, create_new_boolean)
      # do the updating work
    end 
  end
end

Why am I seeing this problem? How do I resolve this?

Answer 1

The problem is, when you put the line Metadata.update_or_add_metadata(new_item, true), it refers to the class Mongoid::Relations::Metadata by default, not the class Metadata you have defined.

Thus you need to give actual path to your Metadata class using scope resolution operator ::. Then there will not be any problem. update_or_add_metadata singleton method defined in the singleton class of the class Metadata you defined, not on the singleton class of Mongoid::Relations::Metadata class.