CODEWITHSUNDEEP
ruby-on-railsrubyinheritanceruby-on-rails-4.1
avatsaev
avatsaev

Reputation: 93

Weird single table inheritance bug in Ruby on Rails

I was working on a Rails application today (Ruby 2.1.3/Rails 4.1) where there is several classes inheriting from a single class Item:

Main class is Item, there is a Page class that inherits from Item and DownloadPage class that inherits from Page class. All objects are stored in a single table and are distinguished by Type column containing object's class name (Page, Article, DownloadPage, etc.)

Here is the UML:

UML

Here what data looks like in the DB (Item table):

DB

Back to the issue, when application loads, and I go to page#index, all objects of type "Page" from Item table are listed, everything is fine, but when the application uses the class DownloadPage at least once (example: DownloadPage.first), page#index sends every object of Page type PLUS objects of type DownloadPage, which is not normal.

Here is a demo of the issue, notice how SQL query only selects Page type the first time (step 1) and Page+DownloadPage the second time (step 3):

enter image description here

So my question is, Am I doing something wrong, architecture might be bad or something else? Or is that a rails/ruby bug

OUTPUT:

2.1.3 :001 > Page.first

Page Load (0.9ms)  SELECT  "items".* FROM "items" WHERE "items"."type" IN ('Page')

=> #<Page id: 2, type: "Page",... 

2.1.3 :002 > DownloadPage.first

DownloadPage Load (0.6ms)  SELECT  "items".* FROM "items"  WHERE "items"."type" IN ('DownloadPage') AND "items"."deleted_at" IS NULL  ORDER BY "items"."id" ASC LIMIT 1

=> #<DownloadPage id: 26, type: "DownloadPage",...

2.1.3 :003 > Page.first

Page Load (1.8ms)  SELECT  "items".* FROM "items"  WHERE "items"."type" IN ('Page', 'DownloadPage')

=> #<Page id: 2, type: "Page", title: "sdfPage"...

Upvotes: 0

Views: 210

Answers (1)

bridiver
bridiver

Reputation: 1714

class Page < Item
end

require_dependency 'download_page'

https://github.com/rails/rails/issues/8699

Upvotes: 3

Related Questions