Rails Single Table Inheritance (STI): Use the same views for different models makes problems with form_for in 'new' action

Question

I have a Boilerplate model which has two descending models:

• BoilerplateOriginal
• BoilerplateCopy

While BoilerplateOriginals is sort of a template that admins create, BoilerplateCopys are copies of the originals that are free to edit by everyone, and they also have some more associated objects (e.g. BoilerplateCopy belongs_to: BoilerplateOriginal, BoilerplateCopy belongs_to: Project or BoilerplateCopy has_many: Findings, all of which BoilerplateOriginal doesn't).

So in my opinion, it makes sense to maintain two different model classes that share the same basic functionalities.

Because they also look quite the same, I want to use the same views for them. But under the hood, they are treated a bit different, so I also have two different controllers inheriting from a base controller.

Everything seems to work fine, except that form_for boilerplate, as: resource_instance_name raises an exception undefined methodboilerplates_path', but only when called asnewaction, not when called asedit` action.

Here's what I have done so far to make it work (and everything else seems to work fine):

# config/routes.rb
resources :boilerplate_originals

# app/models/boilerplate.rb
class Boilerplate < ActiveRecord::Base
  def to_partial_path
    'boilerplates/boilerplate'
  end
end

# app/models/boilerplate_original.rb
class BoilerplateOriginal < Boilerplate
end

# app/controllers/boilerplates_controller.rb
class BoilerplatesController < InheritedResources::Base
  load_and_authorize_resource

  private

  def boilerplate_params
    params.require(:boilerplate).permit(:title)
  end
end

# app/controllers/boilerplate_originals_controller.rb
class BoilerplateOriginalsController < BoilerplatesController
  defaults instance_name: 'boilerplate'
end

# app/views/boilerplates/_form.html.slim
= form_for boilerplate, as: resource_instance_name
  # ...

As pointed out, new/create works flawlessly, but edit doesn't. And I'm using InheritedResources, by the way.

Answer 1

Rails is dong it correctly, you're slightly doing it wrong

the problem is:

resources :boilerplate_originals

that will just generate routes for especially boilerplate_originals. when using form_helpers of rails rails will lookup for a route based on the models class which is in this case "boilerplate_copy". that means its looking for a edit_boilerplate_copy_path (which isnt generated by rails)

You said that BoilerplateCopy and BoilerplateOriginal are pretty much looking the same (i guess you just copy a model, there are gems out for doing that for you...)

If you go correct STI it "should" be

class Boilerplate; end
class BoilerplateCopy < Boilerplate; end
class BoilerplateOriginal < Boilerplate; end

for that you need only a route for Boilerplate

resources :boilerplate

and of course a boilerplate_controller

everything is handled as a boilerplate and the form_helper will look up for a new_boilerplate_path, which exists, no matter if its a copy or a original.

Answer 2

I found the problem.

# app/controllers/boilerplate_originals_controller.rb
class BoilerplateOriginalsController < BoilerplatesController
  defaults instance_name: 'boilerplate' # This is wrong!
  defaults instance_name: 'boilerplate', resource_class: BoilerplateOriginal # This is right!
end

Now a BoilerplateOriginal object is passed to the new action, and not a Boilerplate object.