How to do STI without separate controller per child: Utilize descendent tracking and override model_name so they use the same URL helpers and parameters as their base class. Makes things like responders and form_for work as expected, while preserving things like to_partial_path.

apple_record.rb

class AppleRecord < Record
end

inheritence_base_naming.rb

module InheritanceBaseNaming
  class Name < ActiveModel::Name
    delegate :param_key, :singular_route_key, :route_key, to: :base_name

    def base_name
      @base_name = @klass.base_class.model_name
    end
  end

  def model_name
    Name.new(self)
  end
end

orange_record.rb

class OrangeRecord < Record
end

record.rb

class Record < ActiveRecord::Base
  extend InheritenceBaseNaming

  def [](type)
    descendents.find { |descendent| descendent.name == type }
  end
end

records_controller.rb

class RecordsController < ApplicationController
  before_filter :prepare_records
  before_filter :prepare_record, only: [:show, :edit, :update, :destroy]

  respond_to :html, :json

  def new
    respond_with @record = Record[params.require(:type)].new
  end

  def create
    respond_with @record = Record[params.require(:record_type)].create(record_params)
  end

  def show
    respond_with @record
  end

  def edit
    respond_with @record
  end

  def update
    @record.update_attributes(record_params)
    respond_with @record
  end

  def destroy
    @record.destroy
    respond_with @record
  end

private

  def prepare_records
    @records = Record.scoped
  end

  def prepare_record
    @record = @records.find(params[:id])
  end

  def record_params
    params.require(:record).permit(:name, :content)
  end
end

Results in stack level too deep because model_name on the base_class delegates to model_name on the base_class :)

This fixes:

module InheritanceBaseNaming
  class Name < ActiveModel::Name
    delegate :param_key, :singular_route_key, :route_key, to: :base_name

    def base_name
      @base_name ||= @klass.base_class.model_name
    end
  end

  def model_name
    @model_name ||= (self == base_class) ? super : Name.new(self)
  end
end