Question

我有两个模型，projects和words其中project has_many :words（单词实际上只是一个模型，用于保存每个项目每天写入的单词数量。

我认为我是这样构建的，它显示了项目从开始到结束的所有日子以及当天写了多少单词：

<% project_range(@project.start, @project.end).each do |day| %>
    <%= day %>
    <%= get_word_count_by_date(@project, day ) %>
<% end %>

在我的帮手中：

def project_range(start, finish)
  project_days = (start..finish).collect
end

def get_word_count_by_date(project, date)
  word_count = Word.find_by_project_id_and_wrote_on(project, date)
  if word_count
    word_count.quantity
  else
    0
  end
end

在视图中，麻烦是对我的数据库造成很大影响。例如，如果项目是30天，我得到：

  Word Load (0.2ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-01' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-02' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-03' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-04' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-05' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-06' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-07' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-08' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-09' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-10' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-11' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-12' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-13' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-14' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-15' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-16' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-17' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-18' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-19' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-20' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-21' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-22' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-23' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-24' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-25' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-26' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-27' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-28' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-29' LIMIT 1
  Word Load (0.1ms)  SELECT "words".* FROM "words" WHERE "words"."project_id" = 2 AND "words"."wrote_on" = '2011-09-30' LIMIT 1

有没有办法在没有查询项目长度的每一天的情况下这样做？我首先尝试加载所有项目的单词，但是无法弄清楚如何在那里得到零日。

Answer 1

这是一个“n + 1”问题......您要做的是在查询中加入单词和项目，以便每个项目的所有单词都包含在结果集中。

假设您的项目“has_many：words”：

@project = Project.find(:id, :include => :words)

现在，每个项目的单词集合将预先填充1个查询中的单词。

在“渴望加载关联”http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

下阅读更多内容

Answer 2

您可以使用块帮助程序来保持其清洁并避免查找它们：

def project_range(project, start, finish, &blk)
  words = project.words.where(:wrote_on => start..finish)
  word_map = words.index_by(&:wrote_on)
  for day in start..finish
    word_count = word_map[day] ? word_map[day].quantity : 0
    blk.call(day, word_count)
  end
end

然后像

一样使用它

<% project_range(project, start, finish) do |day, word_count| %>
   <%= day %>
   <%= word_count %>
<% end %>

您也可以稍微清理帮助程序（避免使用SQL），也可以通过传递预取单词列表或使用scope

编辑：m_x建议start..finish where上的wrote_on条款更清晰！

Answer 3

我会选择类似的东西：

@words = @project.words.where("wrote_on >= ? and wrote_on <= ?", start, end)

而不是使用group_by在视图中显示它们：

@words.group_by(&:wrote_on).each do |day, word|
<%= day %>
<%= word.quantity %>
end

减少Rails中的数据库命中

3 个答案: