How to add tags in Ruby on Rails

If you want to add tags, categories, filters, and so on, to your Rails 5 models, the acts-as-taggable-on gem is the way to go. This post will help you set it up.

1. Add it to your Gemfile:

   gem 'acts-as-taggable-on', '~> 6.0'
   

2. Run bundle install.

3. Install its migrations:

   rake acts_as_taggable_on_engine:install:migrations
   

4. Run rake db:migrate.

5. Add acts_as_taggable_on to your model. You don't need to create a migration for your tags – acts-as-taggable-on handles that for you. You can change :tags to anything you'd like – :categories, :codes, etc.

   # post.rb
   class Post < ApplicationRecord
     acts_as_taggable_on :tags
   end
   

6. Then, inside your controller, you'll need to accept :tag_list (or :category_list, or :code_list, etc.) as a strong param. It's the singular version of the word you used in your model, appended with _list.

   # posts_controller.rb
   class PostsController < ApplicationController
     # ...
   
     def post_params
       params.require(:post).permit(:title, :body, :tag_list)
     end
   end
   

7. Now you can add the tags to a form. Sometimes, you may be able to get away with <%= f.input :tag_list %>, but I've had to use a slightly more complicated version in the past. Users can add multiple tags by separating them with commas:

   <!-- views/posts/_form.html.erb -->
   <%= form.label :tag_list, "Tags" %>
   <%=
     form.text_field :tag_list,
     value: @post.send(:tag_list).to_s,
     placeholder: 'rails, development'
   %>
   

8. You can search by tagged filters, as well:

   # routes.rb
   get '/tagged', to: "posts#tagged", as: :tagged
   
   # posts_controller.rb
   def tagged
     if params[:tag].present?
       @posts = Post.tagged_with(params[:tag])
     else
       @posts = Post.all
     end
   end
   

9. And then list each post, plus the option to sort by tags in your view:

   <!-- views/posts/index.html.erb -->
   <% @posts.each do |p| %>
   <h2><%= p.title %></h2>
   <div class="tags">
     <% p.tag_list.each do |t| %>
       <%= link_to t, tagged_path(tag: t) %>
     <% end %>
   </div>
   <% end %>
   

Once you understand how it works, acts-as-taggable-on is a pretty easy gem to use. It has a lot of other features, as well, that you can learn more about on its GitHub page. Have fun tagging!