Use foreign_key in inverse_of relation

mongoid_ext.rb

require 'mongoid/relations/metadata'

class Mongoid::Relations::Metadata
  def determine_inverse_foreign_key
    if has_key?(:inverse_of)
      if inverse_class_name? && inverse_of
        inverse_class_name.constantize.relations[inverse_of.to_s].foreign_key
      else
        inverse_of ? "#{inverse_of.to_s.singularize}#{relation.foreign_key_suffix}" : nil
      end
    else
      "#{inverse_class_name.demodulize.underscore}#{relation.foreign_key_suffix}"
    end
  end
end