I am using Single-Table Inheritance (STI) on one of my models for a
Rails App and I am having problems storing model objects on a constant.
I have isolated the problem into a sample project and submitted it to
GitHub: GitHub - fcoury/rails-sti-caching: Isolated test for Rails Single-Table Inheritance caching problem
What I am trying to do is loading a model instance (in this case a Music
model, that inherits from the Media model via STI) on an initializer (in
Rails’ /config/initializers/ directory) and keep it on a constant:
MUSIC_CACHE = Hash.new
Music.all.each { |m| MUSIC_CACHE[m.id] = m }
And I have a sample controller that does the following:
class MusicsController < ApplicationController
def index
require 'pp'
pp MUSIC_CACHE
@debug = []
MUSIC_CACHE.each_pair do |k, v|
music = Music.find(k)
d "Object for Music.find(#{k}) => class: #{music.class} -
class obj_id: #{music.class.object_id} - #{music.inspect}"
d “Object for MUSIC_CACHE[#{k}] => class: #{v.class} - class
obj_id: #{v.class.object_id} - #{v.inspect}”
begin
d " - Music.is_a?(Media) => #{v.is_a?(Media)}"
d " - Try to call name => #{v.name}"
rescue
d "*** Error raised:\n#{$!}"
end
end
@musics = Music.all
end
def d(s)
puts s
@debug << s
end
end
And a view to go with it:
<h1 id="music">Music</h1>
<ul>
<% for m in @musics %>
<li><%= m.name %> - <%= m.file %></li>
<% end %>
</ul>
<pre><%=h @debug.join("\n") %></pre>
The first time this code runs, the output on the <pre> tag is this:
Object for Music.find(2) => class: Music - class obj_id: 13067420
- #<Music id: 2, name: “5th Symphony”, file: “5s.mp3”, type: “Music”,
created_at: “2009-05-06 16:31:41”, updated_at: “2009-05-06 16:31:41”>
Object for MUSIC_CACHE[2] => class: Music - class obj_id: 13067420 - #<Music id: 2, name: “5th Symphony”, file: “5s.mp3”, type: “Music”,
created_at: “2009-05-06 16:31:41”, updated_at: “2009-05-06 16:31:41”>
- Music.is_a?(Media) => true
- Try to call name => 5th Symphony
However, if I just reload the page, here’s what gets outputted:
Object for Music.find(2) => class: Music - class obj_id: 18452280 -
#<Music id: 2, name: “5th Symphony”, file: “5s.mp3”, type: “Music”,
created_at: “2009-05-06 16:31:41”, updated_at: “2009-05-06 16:31:41”>
Object for MUSIC_CACHE[2] => class: Music - class obj_id: 13067420 -
#<Music id: 2, name: “5th Symphony”, file: “5s.mp3”, type: “Music”,
created_at: “2009-05-06 16:31:41”, updated_at: “2009-05-06 16:31:41”>
- Music.is_a?(Media) => false
*** Error raised:
You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.include?
Does anyone know the rationale behind this error?