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POSafely & efficiently sort on a possibly-missing attribute?
 

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    <p>Here's what I'm doing:</p> <pre><code>offers = v.offers.sort { |a,b| a.expires &lt;=&gt; b.expires } </code></pre> <p>This data is loaded via ActiveResource (so each set of instance attributes is defined by the data it contains). However, a recent change in the incoming data has made the "expires" attribute optional. Is there a class definition change that will cause the sort method to go grab a default value if the attribute is missing from an instance?</p> <p>edit: @Nikita</p> <p>It looks like it won't be that simple:</p> <pre><code>o.expires == nil? NoMethodError: undefined method `expires' for #&lt;Offer:0x00000100d3faa8&gt; o.expires? =&gt; nil </code></pre> <p>so I tried:</p> <pre><code>offers.sort{|a,b| if a.expires? b.expires? ? 0 : -1 else b.expires? ? 1 : a.expires &lt;=&gt; b.expires end } NoMethodError: undefined method `expires' for #&lt;Offer:0x00000100d3faa8&gt; </code></pre> <p>I was hoping to be able to update the class definition with something like:</p> <pre><code>expires ||= "" </code></pre> <p>... but I don't know if that's possible. I don't really follow how the sorting blocks work yet, though. I know I could just loop through the offers and assign the value, but it seems grossly inefficient.</p> <p><strong>update</strong></p> <pre><code>offers.sort{|a,b| if defined? a.expires == nil (defined? b.expires == nil) ? 0 : -1 else (defined? b.expires == nil) ? 1 : a.expires &lt;=&gt; b.expires end } ArgumentError: comparison of Offer with Offer failed from (irb):70:in `sort' from (irb):70 from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.0.beta4/lib/rails/commands/console.rb:47:in `start' from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.0.beta4/lib/rails/commands/console.rb:8:in `start' from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.0.beta4/lib/rails/commands.rb:23:in `&lt;top (required)&gt;' from script/rails:6:in `require' from script/rails:6:in `&lt;main&gt;' </code></pre> <p>Hooray for verbosity ;p</p>
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