重申 collection

Question

我有未知数量的类别。

我想从每个类别中选择一个post，当没有更多类别时我想从头开始，直到达到固定数量post。

这就是我所拥有的，我如何才能重新运行此迭代直到获得我想要的 post 数量？

desired_amount = 40
categories.each_with_index do |category, index|
  post = category.posts.order(position: :asc)[index]
  # do something with the post
  return if desired_amount == (index + 1)
end

Answer 1

也许试试这样的方法？

all_posts = []
#include posts to prevent constant querying the db
categories_with_posts = categories.includes(:posts)

until all_posts.size == 40
 categories_with_posts.each do |category|
   #pick a random post from current category posts
   post = category.posts.order(position: :asc).sample

   # add the post to collection if post is not nil
   all_posts << post if post

   # do something with the post
   break if all_posts.size == 40
 end
end

Answer 2

您可以在开始循环之前定义一个 post 的数组：

desired_amount = 40
posts_array = []
unless posts_array.count == desired_amount 
  categories.each_with_index do |category, index|
    post = category.posts.order(position: :asc)[index]
    posts_array << post
    return if desired_amount == (index + 1)
  end
end

Answer 3

就个人而言，我更喜欢这样的东西：

posts = categories.cycle.take(desired_amount).each_with_index.map do |cat,ind|
  cat.posts.order(position: :asc)[ind / categories.count]
end

这将为您提供每个类别中的第一个 post，然后是每个类别中的第二个 post，依此类推，直到您获得想要的 post 个数。一个警告是，如果任何类别没有足够的 posts，您的最终数组中将有一些空点（即 nils）。

重申 collection

Reiterate over collection

ruby

iteration

ruby-on-rails

ruby-on-rails-5