Ruby在数组中排序哈希有困难

Question

I have a data model that returns the following array:

[[54993, {:posted_at=>1363066554, :item_id=>55007,..}],..]

The 54993 is the post_id. I'm trying to take this array and sort by posted_at . The array comes sorted correctly by posted_at . Here's my current code:

  post_ids = UserFeed.new(current_user.id).posts.collect{|x| x[0]}
  posts = Post.where(:id => post_ids)

This sorts it by post_id , not posted_at . I'm trying to figure out how to sort by posted_at , and wondering why the array resorts by post_id .

Answer 1

If you really need that array in memory instead of sorting your data using a DB query, try this:

method_that_returns_array.sort{ |a, b| a[1][:posted_at] <=> b[1][:posted_at]}

But ordering with a query is the preferred way:

Post.order(:posted_at)

Hope it helps :)

Answer 2

where(ids) does not set order, it uses a SQL IN (id1, id2, ...) . With ActiveRecord:

post_ids = UserFeed.new(current_user.id).posts.map(&:first)
posts = Post.where(:id => post_ids).order("posted_at ASC")

If there is no attribute posts.posted_at , then, solution 1:

posts = post_ids.map { |post_id| Post.find(post_id) }

Solution 2: this performs a single query and then sorts:

indexes = Hash[post_ids.map.with_index.to_a]
posts = Post.where(:id => post_ids).sort_by { |p| indexes[p.id] }

Answer 3

There was a typo in the question that really changes the question, so the first thing that comes to my mind, if the post_ids are sorted correctly is:

posts = []

post_ids.each do |post_id|
    posts << Post.find(post_id)
end