Build correct sti subclass

build_sti_subclass.rb

# STI subclass building backported from Rails 4 to use in Rails 3.2 - see
# https://github.com/rails/rails/commit/89b5b31cc4f8407f648a2447665ef23f9024e8a5
# Usage:
#   include BuildStiSubclass # in your model and be done
module BuildStiSubclass
  extend ActiveSupport::Concern
  included do
    attr_accessible inheritance_column
  end
  module ClassMethods
    # Determines if one of the attributes passed in is the inheritance column,
    # and if the inheritance column is attr accessible, it initializes an
    # instance of the given subclass instead of the base class
    def new(*args, &block)
      if (attrs = args.first).is_a?(Hash)
        if subclass = subclass_from_attrs(attrs)
          return subclass.new(*args, &block)
        end
      end
      # Delegate to the original .new
      super
    end

    # Detect the subclass from the inheritance column of attrs. If the inheritance column value
    # is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
    # If this is a StrongParameters hash, and access to inheritance_column is not permitted,
    # this will ignore the inheritance column and return nil
    def subclass_from_attrs(attrs)
      subclass_name = attrs.with_indifferent_access[inheritance_column]
      return nil if subclass_name.blank? || subclass_name == self.name
      unless subclass = subclasses.detect { |sub| sub.name == subclass_name }
        raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}")
      end
      subclass
    end
  end
end

👍 Nice one