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POProblem caching Model instances on a constant in Rails
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  1. POProblem caching Model instances on a constant in Rails
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    copied!<p>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: <a href="http://github.com/fcoury/rails-sti-caching" rel="nofollow noreferrer">http://github.com/fcoury/rails-sti-caching</a></p> <p>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' <code>/config/initializers/</code> directory) and keep it on a constant:</p> <pre><code>MUSIC_CACHE = Hash.new Music.all.each { |m| MUSIC_CACHE[m.id] = m } </code></pre> <p>And I have a sample controller that does the following:</p> <pre><code>class MusicsController &lt; 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}) =&gt; class: #{music.class} - class obj_id: #{music.class.object_id} - #{music.inspect}" d "Object for MUSIC_CACHE[#{k}] =&gt; class: #{v.class} - class obj_id: #{v.class.object_id} - #{v.inspect}" begin d " - Music.is_a?(Media) =&gt; #{v.is_a?(Media)}" d " - Try to call name =&gt; #{v.name}" rescue d "*** Error raised:\n#{$!}" end end @musics = Music.all end def d(s) puts s @debug &lt;&lt; s end end </code></pre> <p>And a view to go with it:</p> <pre><code>&lt;h1 id="music"&gt;Music&lt;/h1&gt; &lt;ul&gt; &lt;% for m in @musics %&gt; &lt;li&gt;&lt;%= m.name %&gt; - &lt;%= m.file %&gt;&lt;/li&gt; &lt;% end %&gt; &lt;/ul&gt; &lt;pre&gt;&lt;%=h @debug.join("\n") %&gt;&lt;/pre&gt; </code></pre> <p>The first time this code runs, the output on the <code>&lt;pre&gt;</code> tag is this:</p> <pre><code> Object for Music.find(2) =&gt; class: Music - class obj_id: 13067420 - #&lt;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"&gt; Object for MUSIC_CACHE[2] =&gt; class: Music - class obj_id: 13067420 - #&lt;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"&gt; - Music.is_a?(Media) =&gt; true - Try to call name =&gt; 5th Symphony </code></pre> <p>However, if I just reload the page, here's what gets outputted:</p> <pre><code>Object for Music.find(2) =&gt; class: Music - class obj_id: 18452280 - #&lt;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"&gt; Object for MUSIC_CACHE[2] =&gt; class: Music - class obj_id: 13067420 - #&lt;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"&gt; - Music.is_a?(Media) =&gt; 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? </code></pre> <p>Does anyone know the rationale behind this error?</p>
 

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