Question

我在exams_helper.rb中构建了两个方法用于视图：

<% @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 %>

计算主题正确问题数量的方法：

  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

计算正确率百分比的方法

  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

重复这些代码：

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

如何更好地编写这些方法？

Answer 1

在我看来，这些方法应该依赖于您的模型，因为它们的目的是从数据库计算数据。此外，通过在Model层中编写这些方法，可以避免在控制器，视图或视图助手中出现重复。

查看帮助程序只应用于“视图逻辑”方法，这些方法在视图上下文之外没有多大意义。

correct_questions 和比率似乎与ExamResult对象密切相关，我们可以想象以下实现：

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

记忆是一种“缓存”形式，以避免多次重新计算相同的结果。你可以找到很多关于它的文章。这是一个很好的：http://www.railway.at/articles/2008/09/20/a-guide-to-memoization/

最后，您将在视图中包含以下代码。帮助程序不再是必需的，但您仍然可以编写辅助方法来构造“正确/完整”部分，将ExamResult实例 - @exam_result - 作为参数。

<% @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 %>

Answer 2

在你的模特中：

scope :exam,  lambda { |exam_id|  where(exam_id:  exam_id) }
scope :topic, lambda { |topic_id| where(topic_id: topic_id) }
scope :correct, lambda { where(correct: true) }

在你的帮手中：

def get_total_and_correct_count_for(exam_id, topic_id)
  [
   ExamQuestion.exam(exam_id).topic(topic_id).count,
   ExamQuestion.exam(exam_id).topic(topic_id).correct.count
   ]
end

def correct_questions(exam_id, topic_id)
  total, correct = get_total_and_correct_count_for(exam_id, topic_id)
  correct.to_s + '/' + total.to_s
end

def ratio(exam_id, topic_id)
  total, correct = get_total_and_correct_count_for(exam_id, topic_id)
  ratio = (correct.to_f/total).round(2)*100
  if ratio.nan?
    ratio = 0
  else
    ratio
  end
end

旁注：

在帮助程序中执行此类数据库交互感觉很奇怪。
我首先考虑了memoizing，但ActiveRecord提供了内置缓存
如果它在一个循环中，请考虑缓存结果以使它们在请求中保持不变，因为它会损坏db

Answer 3

首先，为什么不在ExamQuestion模型上创建几个方法，而不是每次都使用where？

class ExamQuestion
    #...
    def self.total_count(exam_id, topic_id)
        where(exam_id: exam_id, topic_id: topic_id).count
    end

    # create similar method for "correct" count
 end

然后，我会完全从视图中删除这些db调用。我不喜欢在视图中调用模型的数据库方法，因为它只是在模板文件中编写SQL的一种更好的方法！如果可以，将它们放在控制器操作中并将它们传递给视图：

# Your controller action
@total_count = ExamQuestion.total_count(exam_id, topic_id)
@correct_count = ExamQuestion.correct_count(exam_id,topic_id)
#...

最后，不要将exam_id和topic_id传递给助手，只需传递@total_count和@correct_count即可。好的和小帮手现在：）

消除辅助模块中的重复代码

3 个答案: