Rails get latest n posts per tag

Question

class Post
has_many :tags 

class Tag
belongs_to :post

I need a query that returns all posts limited to n per tag.

Given the following set of posts (tagged with hashtags like on Twitter):

#1: Post A #letter 
#2: Post B #letter
#3: Post 1 #number 
#4: Post C #letter 
#5: Post 2 #number

I would want to get all of the latest 2 posts per tag, giving me the following result:

#5: Post 2 #number 
#4: Post C #letter 
#3: Post 1 #number 
#2: Post B #letter

I've been looking up how to do this for a few hours now, but only found results (like this) that use MySQL variables and don't know how to translate it to Rails.

I still don't know where to begin tackling this so any help is appreciated; thanks!

Read the excellent http://guides.rubyonrails.org/active_record_querying.html — jcm, Jan 01 '14 at 06:58
@summea No, if I use group like in the accepted answer, it would only return one post per tag whereas I'm looking to get multiple (e.g., 5) posts per tag. — , Jan 01 '14 at 07:03
I clarified the question a little more. I'm looking to get the latest n posts for all tags. — , Jan 01 '14 at 07:14
Are you supplying the tags yourself or do you want 'n' latest posts for each tag that exists in db? — erosenin, Jan 01 '14 at 07:44

score 1 · Accepted Answer · edited May 23 '17 at 12:16

1

Try this code

def get_tags(n)
  Tags.order('id desc').select("DISTINCT(NAME)").each do |tag|
    Post.where(tag: tag).limit(n)
  end
end

This link may help you, if not work Unique select from database

edited May 23 '17 at 12:16

Community

1
1

answered Jan 01 '14 at 10:10

Mohamed Yakout

2,868
1
25
45

Richard Peck · Answer 2 · 2014-01-01T10:20:49.533

Maybe you could try:

 @post = Post.joins(:tags).where(tags: {name: "letter"}).order(created_at: :desc).limit(2)

This uses the joins ActiveRecord method, with the hash conditions on the where clause, ordering by created_at (to give latest), and limiting the response to 2 records

This should work for a single tag; if you wanted to extend to multiple tags, I'd use the SQL method GROUP_BY, (ActiveRecord .group), like this:

 @post = Post.joins(:tags).where(tags: {name: "letter", name: "number"}).order(created_at: :desc).group("tags.name").limit(2)

Rails get latest n posts per tag

2 Answers2