How to refactor this Ruby on Rails code?

I want to fetch posts based on their status, so I have this code inside my PostsController index action. It seems to be cluttering the index action, though, and I'm not sure it belongs here.

How could I make it more concise and where would I move it in my application so it doesn't clutter up my index action (if that is the correct thing to do)?

if params[:status].empty?
  status = 'active'
else
  status = ['active', 'deleted', 'commented'].include?(params[:status]) ? params[:status] : 'active'
end

case status
when 'active'
  #active posts are not marked as deleted and have no comments
  is_deleted = false
  comments_count_sign = "="
when 'deleted'
  #deleted posts are marked as deleted and have no comments
  is_deleted = true
  comments_count_sign = "="
when 'commented'
  #commented posts are not marked as deleted and do have comments
  is_deleted = false
  comments_count_sign = ">"
end

@posts = Post.find(:all, :conditions => ["is_deleted = ? and comments_count_sign #{comments_count_sign} 0", 开发者_如何学Gois_deleted])

---

class Post < ActiveRecord::Base
  named_scope :active, :conditions => { :is_deleted => false, :emails_count => 0 }
  named_scope :sent, :conditions => ["is_deleted = ? AND emails_count > 0", true]
  ...
end

use it like Post.active.all, Post.active.first, Post.active.each, etc

and then

status = %w'active deleted sent'.include?(params[:status]) : params[:status] : 'active'
@posts = Post.send(status).all

---

I would consider adding a class method to Post

def file_all_based_on_status status

  # custom logic for queries based on the given status here
  # handling nils and other cases

end

That way your Controller index is simple

def index
  @posts = Post.find_all_based_on_status params[:status]
end