Rails的ActiveRecord的团体成绩为子集按日期 [英] Rails ActiveRecord group results into sub-collections by date

问题描述

我想要做的Rails 3.1的ActiveRecord的查询我的排序结果为子集分组的项目，在这种情况下，按日期进行分组。

I'm trying to do an ActiveRecord query in Rails 3.1 where I sort the results into sub-collections of grouped items, in this case grouped by date.

我觉得我的code最能解释它。这是我的方法，它的作品，但发出4查询完成这项工作。它似乎并不十分有效地做这种方式。

I think my code can explain it best. This is my method, which works but issues 4 queries to get the job done. It doesn't seem very efficient to do it this way.

def entry_days
  days = @user.entry_groups.find(
    :all,
    :select => 'date',
    :limit => 3,
    :group => 'date').map(&:date)

  entry_days = days.map do |date|
    { :date =>  date,
      :entry_groups => @user.entry_groups.find_all_by_date(date)
    }
  end      
end

使用从下面戴夫·牛顿的建议，使用GROUP_BY，我已经重新编写的方法是这样的：

Using the suggestion from Dave Newton below to use group_by, I have re-written the method like this:

def entry_days
  dates_with_entries = @user.entry_groups.find(
    :all,
    :select => 'date',
    :limit => 3,
    :group => 'date').map(&:date)

  @user.entry_groups.where(:date => dates_with_entries).all.group_by(&:date).
    map do |date, entry_groups|
      { :date => date,
        :entry_groups => entry_groups }
    end
end

至少我把它降低到现在只有2查询。

At least I have it down to only 2 queries now.

然后我又重新写了这样的方法：

Then I re-wrote the method again like this:

  dates_with_entries = user.entry_groups.all(
      :select => 'date',
      :limit => num_days,
      :order => 'date DESC',
      :group => 'date').map(&:date)

  entry_groups = user.entry_groups.
      where(
        :date => dates_with_entries
      ).
      all(:order => 'date DESC')

  entry_days = entry_days.group_by(&:date).
      map { |date, entry_groups|
        {
          :date => date,
          :entry_groups => entry_groups
        }
      }

在一个侧面说明：我应该不会链接这么多的方法在一起，什么是preferred缩进格式嵌套方法和散列

On a side note: Should I not be chaining so many methods together, and what is the preferred indentation format for nested methods and hashes?

推荐答案

为什么不选择全部，然后使用类似的 GROUP_BY ？

Why not select them all then use something like group_by?

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