“拆分”ActiveRecord集合

试试这个 group_by 功能开启 Array 班级:

posts.group_by(&:category_id)

参考API documentation

警告:

当潜在的数据集可能很大时,不应该在Ruby代码中执行分组。我使用 当最大可能的数据集大小为<1000在你的情况下,你可能有1000个 Post

下面是一种方法(类似的解决方案由 nas )

# returns the categories with at least one post
# the posts associated with the category are pre-fetched
Category.all(:include => :posts, 
    :conditions => "posts.id IS NOT NULL").each do |cat| 
  cat.posts
end

def split_by_categories(*ids)
  self.inject([]) do |arr, p|
    arr[p.category_id] ||= []
    arr[p.category_id] << p if ids.include?(p.category_id)
    arr
  end.compact
end

与其获取所有的帖子,然后对它们进行一些操作来对它们进行分类,这是一个有点性能密集型的练习,我更愿意像这样使用急切加载

categories = Category.all(:include => :posts)

p = Array.new
categories.each do |category| 
  p[1] = category.posts
  # do anything with p[1] array of posts for the category
end

p = []
1.upto(some_limit) do |n|
  posts = Category.posts.find_by_id(n)
  p.push posts if posts
end