消除在辅助模块

Question

我已经建立了exams_helper.rb两种方法在视图中使用重复的代码：

<% @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 %> 

法计算话题的正确问题编号：

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 

方法来计算百分比的正确性

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 

这些代码被重复：

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 

我该怎么写这些方法更好？

Answer 1

在我看来，这些方法应该依赖于你的模型，因为他们的目的是从数据库中计算数据。另外，通过在Model层中编写这些方法，可以避免控制器，视图或视图助手中的重复。

视图助手只应该用于'视图 - 逻辑'方法，这些方法在视图上下文之外没有多少意义。

correct_questions和比似乎是密切相关的ExamResult对象，我们可以设想以下实现：

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 

记忆化是“缓存”形式，以避免重复计算相同的结果很多倍。你可以找到很多关于它的文章。这里是一个很好的一个：http://www.railway.at/articles/2008/09/20/a-guide-to-memoization/

最后，你会在你的视图下面的代码。助手是不是真的有必要了，但你仍然可以写一个辅助方法，构建了“正确/总”的一部分，服用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

在你的模型：

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) } 

在您的帮助：

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 

---

图片的标题说明：

• 感觉怪异内执行这种数据库的交互帮手。

• 我首先考虑memoizing但ActiveRecord的提供了一个内建的缓存

• 如果它是在一个循环中考虑缓存的结果让他们坚持之中请求，因为它伤害了分贝

Answer 3

首先，为什么不是在ExamQuestion模型上创建几个方法，而是每次都使用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，我将这些数据库调用完全从视图中取出。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的更好方法！如果可以，将它们放在控制器动作，并通过他们下到视图：

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

最后，强似exam_id和topic_id到你的助手，只是通过@total_count和@correct_count。尼斯和小帮手现在:)