Rails sorting associations with Ransack - ruby-on-rails-3

Question

first time poster. I am trying to sort a table of users using the Ransack gem and Kaminari for pagination. When I use name, id, etc. sorting works but when I try an association with posts_count, sorting breaks and won't work. Note: in the view, 'u.posts.count' work correctly. I have tried custom scopes in the users model, and creating custom objects for the search params but nothing seems to work. I think I am having trouble either in the default scope or the #search object not having the data. Need help!
Here are some relevant snippets:
models/user.rb
has_many :posts, :dependent => :destroy
models/post.rb
belongs_to :user
default_scope :order => 'post.created_at DESC'
controllers/users_controller.rb
def index
#title = "User Index"
#search = User.search(params[:q]) # Ransack
#total_users = User.all.count
# .per(10) is the per page for pagination (Kaminari).
#users = #search.result.order("updated_at DESC").page(params[:page]).per(10) #This displays the users that are in the search criteria, paginated.
end
views/users/index.html.erb
..
<%= sort_link #search, :posts_count, "No. of Posts" %> #Sort links at column headers
..
<% #users.each do |u| %> #Display everything in the table
<%= u.posts.count %>
<% end %>

Answer 1

You can add a scope to your User model:
def self.with_posts
joins(:posts).group('posts.id').select('users.*, count(posts.id) as posts_count')
end
and use it like this:
#search = User.with_posts.search(params[:q]) # Ransack
then, you can treat posts_count like any other attribute.

Answer 2

I found a solution:
Controller:
def index
sql = "users.*, (select count(posts.id) from posts\
where posts.user_id = users.id) as count"
#search = User.select(sql).search(params[:q])
if params[:q] && params[:q][:s].include?('count')
#users = #search.result.order(params[:q][:s])
else
#users = #search.result
end
.......
end
View:
<th><%= sort_link #search, :count, "posts count" %></th>