I am working on a rails 3.2 app that basically acts as a blog with tags.

Tags are related to posts in a has\_many :through association. (post have many tags through taggigns)
Don't know why the app doesn't have a habtm association since it would have worked the same, but that's what I have.

The app can now show the list of posts belonging to a tag like this:

```
class TagsController < ApplicationController

  def show
    @tag = Tag.find(params[:id])    
    @posts = @tag.posts.paginate(page: params[:page], :per_page => 10) 
  end
  ...
end

```

This way the page example.com/tags/1 will show all the posts with a tag matching ID 1.

What I have to do is modify this app to have checkboxes for tags and to restrict the search for example to posts having both tag 1 and 4.

Can someone please give me an input on where to start or maybe some resources to look for? I think I should use a join but I'm not sure this is the case.

Thank you.

========

EDIT: Thank you for your answers. Anyway, as suggested by ok32, user1083138's solutions was creating duplicates. At the same time ok32's one was resulting in empty arrays (probably it's due to my poor implementation of the tagging system).

I went up with this solution that works just fine:

```
  def self.tag_query(list)
    Post.joins(:tags).where(:tags => { :name => list } ).having("count(tags.name) = ?", list.count ).group('posts.id')
  end

```