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POWhy are Rails scopes preferable, if messy controllers are faster?
 

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  1. POWhy are Rails scopes preferable, if messy controllers are faster?
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    <p>I've been trying to chain Arel queries using scopes, instead of just using some long-winded logic I wrote in the controller. But the scopes are slower than just getting all the records and then sifting through them with some logic. I'm wondering, then, why scopes are better.</p> <p>Here's what I'm doing:</p> <ul> <li>a question has many answers</li> <li>an answer belongs to one question</li> <li>a question has a "question_type" column that I use to sort it</li> </ul> <p><strong>First, the scopes way...</strong></p> <p>in question.rb:</p> <pre><code>scope :answered, joins(:answers).order('answers.created_at desc') scope :dogs, where(:question_type =&gt; "dogs") scope :cats, where(:question_type =&gt; "cats") scope :mermaids, where(:question_type =&gt; "mermaids") </code></pre> <p>in questions_controller.rb:</p> <pre><code>@dogs_recently_answered = Question.answered.dogs.uniq[0..9] @cats_recently_answered = Question.answered.cats.uniq[0..9] @mermaids_recently_answered = Question.answered.mermaids.uniq[0..9] </code></pre> <p>Then in the view, I cycle through those instance variables (which are now arrays containing at most 10 elements) and display the results.</p> <p><em>Here are the times it takes to load the page (five different times):</em></p> <p>Completed 200 OK in 535ms (Views: 189.6ms | ActiveRecord: 46.2ms)</p> <p>Completed 200 OK in 573ms (Views: 186.0ms | ActiveRecord: 46.3ms)</p> <p>Completed 200 OK in 577ms (Views: 189.0ms | ActiveRecord: 45.6ms)</p> <p>Completed 200 OK in 532ms (Views: 182.9ms | ActiveRecord: 46.1ms)</p> <p>Completed 200 OK in 577ms (Views: 186.7ms | ActiveRecord: 46.9ms)</p> <p><strong>Now, the messy controller way...</strong></p> <pre><code>@answers = Answer.order("created_at desc") @all_answered = [] @answers.each {|answer| @all_answered &lt;&lt; answer.question} @recently_answered = @all_answered.uniq @dogs_all_answered = [] @cats_all_answered = [] @mermaids_all_answered = [] @recently_answered.each do |q| if q.question_type == "dogs" @dogs_all_answered &lt;&lt; q @dogs_recently_answered = @dogs_all_answered[0..9] elsif q.question_type == "cats" @cats_all_answered &lt;&lt; q @cats_recently_answered = @cats_all_answered[0..9] elsif q.question_type == "mermaids" @mermaids_all_answered &lt;&lt; q @mermaids_recently_answered = @mermaids_all_answered[0..9] end end </code></pre> <p><em>And here are the times it takes to load the page now (five different times):</em></p> <p>Completed 200 OK in 475ms (Views: 196.5ms | ActiveRecord: 34.5ms)</p> <p>Completed 200 OK in 480ms (Views: 200.4ms | ActiveRecord: 36.4ms)</p> <p>Completed 200 OK in 434ms (Views: 198.2ms | ActiveRecord: 35.8ms)</p> <p>Completed 200 OK in 475ms (Views: 194.2ms | ActiveRecord: 36.4ms)</p> <p>Completed 200 OK in 475ms (Views: 195.0ms | ActiveRecord: 35.4ms)</p> <p><strong>So...</strong></p> <p>Aside from readability, what's to be won by honing the query with a scope? Does it eventually become quicker when there are more records?</p>
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