Question

I have built two methods in exams_helper.rb to use in views:

<% @topic_questions.each do |topic_question| %>
<tr>
  <td><%= topic_question.topic.name %></td>
  <td><%= correct_questions(@exam_result.exam_id, topic_question.topic_id) %></td>
  <td><%= number_to_percentage(ratio(@exam_result.exam_id, topic_question.topic_id), precision: 0) %></td>
</tr>
<% end %>

Method to calculate the number of correct question of topic:

  def correct_questions(exam_id, topic_id)
    total = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id).count
    correct = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id, correct: true).count
    correct.to_s + '/' + total.to_s
  end

Method to calculate percentage of correctness

  def ratio(exam_id, topic_id)
    total = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id).count
    correct = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id, correct: true).count
    ratio = (correct.to_f/total).round(2)*100
    if ratio.nan?
      ratio = 0
    else
      ratio
    end
  end

These code is repeated:

total = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id).count
correct = ExamQuestion.where(exam_id: exam_id, topic_id: topic_id, correct: true).count

How can I write these method better?

Answer 1

In my opinion, these methods should rely in your Model as their purpose is to compute data from Database. Also, by writing these methods in the Model layer, you can avoid duplication in controllers, views or view helpers.

View helpers should only be used for ‘view-logic’ methods, that do not make much sense outside of the view context.

correct_questions and ratio seem to be closely related to the ExamResult object, we could imagine the following implementation:

class ExamResult
  has_many :exam_questions

  def correct_questions_ratio(topic)
    ratio = (correct_questions(topic).to_f/total_questions(topic)).round(2)*100

    if ratio.nan?
      ratio = 0
    else
      ratio
    end
  end

  def total_questions(topic)
    #To avoid recomputing the result from db we memoize it for each topic.
    @total_questions ||= {}
    @total_questions[topic] ||= exam_questions.where(:topic_id => topic.id).count
  end

 def correct_questions(topic)
   #To avoid recomputing the result from db we memoize it for each topic.
   @correct_questions ||= {}
   @correct_questions[topic] ||= exam_questions.where(:topic_id => topic.id, :correct => true).count
 end
end

Memoization is a form of “caching” to avoid recomputing the same result many times. You can find many articles about it. Here is a good one : http://www.railway.at/articles/2008/09/20/a-guide-to-memoization/

Finally, you would have the following code in your view. The helper is not really necessary anymore, but you can still write a helper method to construct the “correct/total” part, taking an ExamResult instance – @exam_result – as a parameter.

<% @topic_questions.each do |topic_question| %>
  <tr>
    <td><%= topic_question.topic.name %></td>
    <td><%= @exam_result.correct_questions(topic_question.topic) %>/<%= @exam_result.total_questions(topic_question.topic)%></td>
    <td><%= number_to_percentage(@exam_result.correct_questions_ratio(topic_question.topic)), precision: 0) %></td>
  </tr>
<% end %>