Question

我有一个Sleep模型，其实例belongs_to是Person模型的实例。我想将统计计算传递给后台线程。人们自我报告他们的数据，并可能会跳过几天。

我创建了一个Sleepstat模型，并计划计算每天有一个或多个记录的Sleep实例的统计信息。但是，人们可以稍后返回并编辑他们的数据，因此在此后台任务中，我想扫描Sleepstat的现有实例以确定needs_updating标志的状态。

如果有人在某天没有现有Sleep的情况下创建Sleepstat记录，那么我希望后台任务创建Sleepstat并计算当天的统计信息。如果有人在现有Sleep的日期添加了额外的Sleepstat记录，那么我想将Sleepstat标记为需要更新并使用新数据更新，以保持统计信息-至今。

我的想法是做以下事情：

运行查询以返回属于相关Sleep的所有Person条记录。为此，我使用了这个查询，它按照我的预期运行：
```
all_sleeps = Sleep.select('start_time,end_time,multiday,time_zone,in_progress').where(:person_id => self.id)
```

创建唯一start_time日期的数组：

days_recorded = []
  for sleep in all_sleeps
    days_recorded.push sleep.start_time.to_date
  end
  days_recorded = days_recorded.uniq

对于days_recorded中的每一个，请查看是否存在Sleepstat。如果没有，请创建一个并计算统计数据。如果是，请检查是否needs_updating。如果是，请计算统计数据。如果没有，请转到days_recorded中的下一个项目。

days_recorded.each do |d|
    stat = Sleepstat.where(:date => d).first

    if stat.nil?
      # No record, so create one because we have data for that day and calculate stats
      ...

    else
      # There is a record. Evaluate whether it needs to be updated

      if stat.needs_updating?
        # Update the Sleepstat
        ...

      end

    end
end

这种方法导致了许多独立的查询：

Sleepstat Load (0.2ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" = '2011-12-10'
Sleepstat Load (0.2ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" = '2011-12-11'
Sleepstat Load (0.2ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" = '2011-12-12'
Sleepstat Load (0.2ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" = '2011-12-13'

我的想法是先尝试通过以下查询抓取所有Sleepstat：

existing_stats = Sleepstat.where(:date => days_recorded)

然后在步骤3中迭代它们。我的尝试看起来像：

    existing_stats = Sleepstat.where(:date => days_recorded)

    days_recorded.each do |d|
        stat = existing_stats.where(:date => d)

        if stat.nil? || stat.length == 0
          # No record, so create one because we have data for that day and calculate stats
          ...

        else
          # There is a record. Evaluate whether it needs to be updated

          if stat.needs_updating?
            # Update the Sleepstat
            ...

          end

        end
    end

这导致了许多更复杂的个人查询：

Sleepstat Load (0.5ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" IN ('2011-12-07', '2011-12-06', '2011-12-08', '2011-12-09', '2011-12-10', '2011-12-11', '2011-12-12', '2011-12-13', '2011-12-14', '2011-12-15') AND "sleepstats"."date" = '2011-12-10'
Sleepstat Load (0.9ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" IN ('2011-12-07', '2011-12-06', '2011-12-08', '2011-12-09', '2011-12-10', '2011-12-11', '2011-12-12', '2011-12-13', '2011-12-14', '2011-12-15') AND "sleepstats"."date" = '2011-12-11'
Sleepstat Load (0.6ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" IN ('2011-12-07', '2011-12-06', '2011-12-08', '2011-12-09', '2011-12-10', '2011-12-11', '2011-12-12', '2011-12-13', '2011-12-14', '2011-12-15') AND "sleepstats"."date" = '2011-12-12'
Sleepstat Load (0.4ms)  SELECT "sleepstats".* FROM "sleepstats" WHERE "sleepstats"."date" IN ('2011-12-07', '2011-12-06', '2011-12-08', '2011-12-09', '2011-12-10', '2011-12-11', '2011-12-12', '2011-12-13', '2011-12-14', '2011-12-15') AND "sleepstats"."date" = '2011-12-13'

如何提高此过程的效率，以免我多次访问数据库？

Answer 1

如果您的统计数据不是太重而无法计算，那么最好使用callback 每次创建或更新记录时计算统计数据：

Class Sleep < ActiveRecord::Base
  before_save :create_or_update_stats

  def create_or_update_stats
    # avoid calculation if record is new or if nothing changed
    return unless ( self.new_record? || self.changed? ) 

    date = self.start_time.to_date
    stats  = Sleepstat.find_or_create_by_date( date )
    sleeps = Sleep.where( date: date )

    # now calculate the stats and save them.
  end
end

编辑当然，你也必须在destroy上添加一个回调。你得到了精神。

额外提示：

不要使用for语法。它在内部调用each，为什么要这么麻烦？

这与你在2）中所做的相同：

all_sleeps.map{|s| s.start_date.to_date }.uniq
# or even this
all_sleeps.map( &:start_date ).map( &:to_date ).uniq

测试关系是否为空，请使用stat.exists?代替您的陈述
如果你真的需要做大量的计算，你应该看看arel tables因为它们允许你跳过记录实例并只加载你需要的数据，提供一个很好的提升

如何使这组Rails 3.1查询更有效？

1 个答案: