Invalid single-table inheritance type: SubClass is not a subclass of Class

[PhilCoggins]

I encountered some serious headaches while working with Elasticsearch-Model in development.

My problem is that the Invalid single-table inheritance type: X is not a subclass of Y exception was being thrown when I tried to instantiate records with the Multiple adapter after my code had been reloaded for the first time. I would have to restart my Rails server every time I made any changes to my code.

What I found was that Elasticsearch::Model::Registry.models would endlessly accumulate reloaded classes each time my code was being reloaded. If I had five classes that included Elasticsearch::Model, it would increase by 5 each time my code reloaded. I have monkey-patched the Registry class with:

  module Elasticsearch
    module Model
      class Registry
        def add(klass)
+         existing_model = @models.detect { |model| model.name == klass.name }
+         @models.delete(existing_model)
          @models << klass
        end
      end
    end
  end

in an initializer and only for development environment to fix this particular issue to ensure this Registry only contains the newly-reloaded classes.

After this change, I continued to encounter the same error. What I found was that Elasticsearch::Model::Adapter::Multiple::Records was caching the result of __type_for_hit in a class variable @@__types, and after my code was reloaded, the stale classes were being returned instead of the newly reloaded classes. I unset this class variable by hooking into Active Support's reloader:

Rails.application.reloader.before_class_unload do
  Elasticsearch::Model::Adapter::Multiple::Records.remove_class_variable(:@@__types) }
end

This is in the same environment block that the above monkey-patch is in to avoid affecting production environment. This allowed my records to be instantiated even after my code had been reloaded and fixed my issue.

This issue took a ton of time and effort (and frustration) to debug and fix, it would be nice to see the team provide better support for STI since this is a core feature in Rails. Hopefully this report will help you guys improve on some of these weak spots. I'm happy to provide any other information you might need.

[estolfo]

Hi @PhilCoggins Thanks for raising this issue. Would you mind providing an example so we can reproduce it?

[PhilCoggins]

Thanks @estolfo, here is a sample app with instructions:

https://github.com/PhilCoggins/elasticsearch-sti-fail

LMK if you have any issues running. I tried to do this in a single script file but ActiveSupport::Reloader.reload would not trigger the error for some reason.

[darkhelmet]

I'm also hitting this, will use the initializer patches for now.

[darkhelmet]

Looking at the code, I wonder if it makes sense to use the before_class_unload hook to empty the @models array as well.

[PhilCoggins]

@darkhelmet You could, though that's already occurring in the Elasticsearch::Model::Registry#add monkey patch (we remove a model if there's already one there with the same constant name).

Also want to point out that the initializer is wrapped in an environment check since I only need this on dev, not sure how it would behave in prod.

[darkhelmet]

Yeah, this is what I ended up with in my initializer.

if Rails.env.development?
  Rails.application.reloader.before_class_unload do
    Elasticsearch::Model::Registry.remove_instance_variable(:@instance)
    Elasticsearch::Model::Adapter::Multiple::Records.remove_class_variable(:@@__types)
  end
end

[surjay]

Is there any movement on a gem fix for this? I just ran into this and its a major issue. It only happens for me in Rails5, though which we are currently upgrading to. I've never encountered this in Rails4.

[estolfo]

@surjay I will look into it and have an update soon!

[estolfo]

@PhilCoggins I'm having trouble reproducing this using the example app you provided. I followed the steps in the README. Is there anything I'm missing below?

2.5.1 :001 > require_dependency 'animal'
 => true 
2.5.1 :002 > Elasticsearch::Model.search("Fluffy")
 => #<Elasticsearch::Model::Response::Response:0x00007f8018591588 @klass=#<Elasticsearch::Model::Multimodel:0x00007f80185932c0 @models=[Animal (call 'Animal.connection' to establish a connection)]>, @search=#<Elasticsearch::Model::Searching::SearchRequest:0x00007f80185930b8 @klass=#<Elasticsearch::Model::Multimodel:0x00007f80185932c0 @models=[Animal (call 'Animal.connection' to establish a connection)]>, @options={}, @definition={:index=>["animals"], :type=>["_doc"], :q=>"Fluffy"}>> 
2.5.1 :004 > reload!
Reloading...
 => true 
2.5.1 :005 > Elasticsearch::Model.search("Fluffy")
 => #<Elasticsearch::Model::Response::Response:0x00007f801da14380 @klass=#<Elasticsearch::Model::Multimodel:0x00007f801da146f0 @models=[Animal (call 'Animal.connection' to establish a connection)]>, @search=#<Elasticsearch::Model::Searching::SearchRequest:0x00007f801da14600 @klass=#<Elasticsearch::Model::Multimodel:0x00007f801da146f0 @models=[Animal (call 'Animal.connection' to establish a connection)]>, @options={}, @definition={:index=>["animals"], :type=>["_doc"], :q=>"Fluffy"}>> 
2.5.1 :006 > Elasticsearch::Model::Registry.all
 => [Animal (call 'Animal.connection' to establish a connection)] 
2.5.1 :007 > reload!
Reloading...
 => true 
2.5.1 :008 > Elasticsearch::Model::Registry.all
 => [Animal (call 'Animal.connection' to establish a connection)] 

[PhilCoggins]

@estolfo thanks for reaching back out.

I have updated the instructions in the repo. Also make sure you run the setup instructions at the top (rails db:migrate and rails runner script.rb)

[estolfo]

@PhilCoggins I've opened this pull request but I get a (ActiveRecord::SubclassNotFound) error when I test it with your example app. Maybe there's something else that needs to change in the example app to fully test the changes. I'll work on adding tests but I wanted to get the PR up asap so you could take a look and let me know what you think.

[PhilCoggins]

I would consider the ActiveRecord::SubclassNotFound a derivative of the core issue.

Somehow, when a klass is first added to the @models array, it initially contains no descendants, but subsequently performing a search the descendant is added.

When code is reloaded, however, the klass is added to the @models array, and a search is performed, the descendants don't get added.

Using your branch of elasticsearch-model on my test project:

irb(main):001:0> require_dependency 'animal'
=> true
# Open connection
irb(main):002:0> Animal.connection
# Animal is in registry
irb(main):003:0> Elasticsearch::Model::Registry.all
=> [Animal(id: integer, name: text, type: text)]
# The model contains no descendants (ActiveRecord has not yet loaded this class)
irb(main):004:0> Elasticsearch::Model::Registry.all[0].descendants
=> []
irb(main):005:0> Elasticsearch::Model.search("Fluffy").records.to_a
=> [#<Dog id: 4, name: "Fluffy", type: "Dog">]
# Descendants now show up
irb(main):006:0> Elasticsearch::Model::Registry.all[0].descendants
=> [Dog(id: integer, name: text, type: text)]
irb(main):007:0> reload!
Reloading...
=> true
# Code reloaded, registry updated with new class, no descendants
irb(main):008:0> Elasticsearch::Model::Registry.all[0].descendants
=> []
# Blows up
irb(main):009:0> Elasticsearch::Model.search("Fluffy").records.to_a
Traceback (most recent call last):
        1: from (irb):9
ActiveRecord::SubclassNotFound (The single-table inheritance mechanism failed to locate the subclass: 'Dog'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Animal.inheritance_column to use another column for that information.)

I hope this helps.