Rails Admin doesn't handle STI to single table

[Naokimi]

I have 2 different classes inheriting from User but saving in the same table:

class User < ApplicationRecord
  # devise stuff
end

class Participant < User
  has_many :participant_stamps
  has_many :stamps, through: :participant_stamps
end

class Vendor < User
  has_many :vendor_stamps
  has_many :stamps, through: :vendor_stamps
end

I'd like to add a VendorStamp using rails admin, but when I go to the tab, the relation is missing, which of course throws an error when trying to save

I also tried to explicitly tell it to look for a vendor (see below), but with no luck

RailsAdmin.config do |config|
  config.model 'VendorStamp' do
    list do
      field :stamp
      field :vendor
    end
  end
end

[mshibuya]

Could you provide all relevant information like the VendorStamp model?
Are the operation you're trying to do achievable using the Rails Console?

[Naokimi]

VendorStamp model:

class VendorStamp < ApplicationRecord
  belongs_to :stamp
  belongs_to :vendor

  validates :stamp_id, uniqueness: { scope: :vendor_id }
end

Stamp model:

class Stamp < ApplicationRecord
  has_many :vendor_stamps
  has_many :vendors, through: :vendor_stamps
  has_many :participant_stamps
  has_many :participants, through: :participant_stamps
end

Creating VendorStamp in Rails Console (and confirming that it was actually created):

[Naokimi]

to point it out again: Vendor and Participant both save their record in the users table, thanks to this migration:

class DeviseCreateUsers < ActiveRecord::Migration[6.1]
  def change
    create_table :users do |t|
      ## Database authenticatable
      t.string :email,              null: false, default: ""
      t.string :encrypted_password, null: false, default: ""
      t.string :type #this column is what allows to save different Models in one table

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      t.timestamps null: false
    end

    add_index :users, :email,                unique: true
    add_index :users, :reset_password_token, unique: true
  end
end

[Naokimi]

if you want to generate the other models, here are the migrations:

class CreateStamps < ActiveRecord::Migration[6.1]
  def change
    create_table :stamps do |t|
      t.string :name
      t.string :img_url

      t.timestamps
    end
  end
end

class CreateParticipantStamps < ActiveRecord::Migration[6.1]
  def change
    create_table :participant_stamps do |t|
      t.references :stamp, null: false, foreign_key: true
      t.references :participant, null: false, foreign_key: { to_table: :users }

      t.timestamps
    end
  end
end

class CreateVendorStamps < ActiveRecord::Migration[6.1]
  def change
    create_table :vendor_stamps do |t|
      t.references :stamp, null: false, foreign_key: true
      t.references :vendor, null: false, foreign_key: { to_table: :users }

      t.timestamps
    end
  end
end

[mshibuya]

I can't reproduce by using exactly the same setup, the vendor field shows up normally.

Can you show me the whole content of your VendorStamp model and RailsAdmin config?

[Naokimi]

VendorStamp I copied whole content

this is my rails admin config:

require 'nested_form/engine'
require 'nested_form/builder_mixin'

RailsAdmin.config do |config|

  ### Popular gems integration

  ## == Devise ==
  config.authenticate_with do
    warden.authenticate! scope: :user
  end
  config.current_user_method(&:current_user)

  ## == CancanCan ==
  # config.authorize_with :cancancan

  ## == Pundit ==
  # config.authorize_with :pundit

  ## == PaperTrail ==
  # config.audit_with :paper_trail, 'User', 'PaperTrail::Version' # PaperTrail >= 3.0.0

  ### More at https://github.com/sferik/rails_admin/wiki/Base-configuration

  ## == Gravatar integration ==
  ## To disable Gravatar integration in Navigation Bar set to false
  # config.show_gravatar = true

  config.authorize_with do
    unless current_user.admin?
      flash[:alert] = 'Sorry, no admin access for you.'
      redirect_to main_app.root_path
    end
  end

  config.actions do
    dashboard                     # mandatory
    index                         # mandatory
    new
    export
    bulk_delete
    show
    edit
    delete
    show_in_app

    ## With an audit adapter, you can add:
    # history_index
    # history_show
  end
end

To check for admin permissions I set up these methods in my User model:

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :validatable

  def admin?
    instance_of?(Admin)
  end

  def participant?
    instance_of?(Participant)
  end

  def vendor?
    instance_of?(Vendor)
  end
end

[Naokimi]

Ruby -v 2.7.2
Rails -v 6.1.4

[mshibuya]

Hmm, I see nothing unusual.

This is the repo I've created trying to reproduce this issue, can you make that happen by using this?
https://github.com/mshibuya/issue-3373

[Naokimi]

I was able to run the repo you provided, but then I tried creating a new one more similar to the one I have and the error is the same.

You can find the repo here: https://github.com/Naokimi/rails-admin-issue-3373

The main differences are:

• using PG instead of sqlite
• inheritance models are under app/models/users/ folder
• added to config/application.rb the line config.autoload_paths += %W(#{Rails.root}/app/models/users)

BUT

when I kept all the models inside app/models and removed the added line, it worked as expected

Is there a way how to make it work while at the same time keeping models in folders for better readability?

[mshibuya]

Thanks, I was able to track down the issue.

First, you need to use eager_load_paths instead of autoload_paths.

  config.eager_load_paths += %W(#{Rails.root}/app/models/users)

autoload_paths is just telling the Rails to load models if necessary, hence the Vendor model fails to be picked up by RailsAdmin.
https://stackoverflow.com/a/19852844

But that alone does not solve this issue, there was a glitch in RailsAdmin which ignores the application-specific eager_load_paths configuration. 238f18e addresses it.

In short, using eager_load_paths and using the RailsAdmin master branch will solve this.

[Naokimi]

Sorry for coming back to this after so long, but just wanted to say that it still doesn't work :(

I've updated the gem and added the eager_load_paths

you can find the code in https://github.com/Naokimi/rails-admin-issue-3373

[mshibuya]

The fix is not released yet, you need to use the master branch.

gem 'rails_admin', github: 'sferik/rails_admin'