Polymorphic association dropdown

[alina-ep]

Hi! I’m upgrading from rails_admin 0.0.5 to 3.1.2 and I’m having issues with polymorphic select forms/dropdown.

It worked great in rails 3, but not in rails 7. I have these 4 models with polymorphic relations:

class Source < ActiveRecord::Base
  belongs_to :resource_item, polymorphic: true, inverse_of: :sources
end

class SourceItem < Source
end

class SheetMusicPiece < ActiveRecord::Base
  has_many :sources, as: :resource_item, inverse_of: :resource_item
end

class SourceCollection < Source
  has_many :sources, :as => :resource_item, :inverse_of => :resource_item
end

The way it used to work was that when I created a new SourceItem in the admin, it would generate a dropdown containing model names like "SheetMusicPiece" and "SourceCollection". Once I chose the model name, it would then generate a dropdown of instances of that model from which I could choose one to associate a new object with

This is a rails admin config in initializer:

config.model SourceItem do
    list do
      field :resource_item do
        help 'Required'
      end
    end
    edit do
      field :resource_item
    end
end

Expectation (rails 3):

Rails 7:

My Gemfile:

source 'http://rubygems.org'
ruby '3.0.1'

gem 'activemerchant', '~> 1.99.0'
gem 'active_shipping'
gem 'cancan'
gem 'ckeditor', '4.3.0'
gem 'devise', '~> 4.9.2'
gem 'erubis'
gem 'exception_notification', '~> 4.5'
gem 'execjs'
gem 'jquery-rails', '~> 4.5.1'
gem 'jquery-ui-rails', '~> 6.0', '>= 6.0.1'
gem 'haml', '~> 6.1', '>= 6.1.1'
gem 'kaminari'
gem 'kt-paperclip', '~> 7.1', '>= 7.1.1'
gem 'mysql2' # required by thinking-sphinx
gem 'nio4r', '~> 2.4.0'
gem 'nokogiri', '~> 1.14', '>= 1.14.2'
gem 'paper_trail', '~> 14.0'
gem 'pg', '~> 1.4.6'
gem 'pdf-core', '~> 0.9.0'
gem 'pdf-reader'
gem 'prawn', '~> 2.4'
gem 'rack-ssl-enforcer'
gem 'rails', '~> 7.0', '>= 7.0.4.3'
gem 'rails_admin', '~> 3.0.0'
gem 'rails_admin_import', '~> 3.0.3'
gem 'responders', '~> 3.1'
gem 'rexml', '~> 3.2', '>= 3.2.5'
gem 'rubyzip', '~> 1.0'
gem 'sprockets-rails', '~> 3.4', '>= 3.4.2'
gem 'therubyracer'
gem 'thinking-sphinx', '~> 5.5', '>= 5.5.1'
gem 'tilt'
gem 'ttfunk', '~> 1.7.0'
gem 'unicorn-rails', '~> 2.2'
gem 'unicorn', '~> 6.1'

# Install iconv gem to prevent errors after Ruby 2.1 upgrade
gem 'iconv', '~> 1.0.4'

# Gems used only for assets and not required in production environments by default.
group :assets do
  gem 'sass-rails', "~> 5.1.0"
  gem 'coffee-rails', "~> 5.0.0"
  gem 'uglifier', '~> 3.0'
end

group :development, :test do
  gem 'byebug', '~> 10.0'
end

group :development do
  gem 'spring', '~> 3.1.1'
end

gem 'rack-utf8_sanitizer'
gem "sassc-rails"

I did a bit of digging and found that the potential issue is in rails_admin-3.1.2/lib/rails_admin/config/fields/types/polymorphic_association.rb and how the entire form is being constructed, specifically when setting associated_model_config:

def associated_model_config
   @associated_model_config ||= association.klass.collect { |type| RailsAdmin.config(type) }.reject(&:excluded?)
end

when running this in the console for my polymorphic association:

irb(main):003:0> Source.reflect_on_association(:resource_item).klass
/home/user/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.4.3/lib/active_record/reflection.rb:423:in `compute_class': Polymorphic associations do not support computing the class. (ArgumentError)

so when it comes to constructing the form in rails_admin-3.1.2/app/views/rails_admin/main/_form_polymorphic_association.html.erb

The type_collection variable is nil, which is why there are no dropdown options in the DOM.

So my question is: Is this a bug, or is the functionality I'm expecting no longer supported? Please, advice what should I do in this situation, I’m getting kind of desperate trying to make it work

Thanks!

[mshibuya]

I could confirm the issue and made the fix as https://github.com/railsadminteam/rails_admin/commit/2a89ebcfa96243697988f6570b9c9be19a7a01b5. Thank you for reporting, and also being a long-time user!

[alina-ep]

Thank you!