Rails 3/4 gem that allows you to easily add slugs to your website.
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What is Inferred Slug ?

Most slug engines require you to modify your database schema to save slugs in it. The idea behind Inferred Slug is that slugs can be inferred and treated as logic, instead of being treated as data.

This gem is compatible with the rest of slug engines, as far as I know. If you find any incompatibility, I'd be glad to hear about it, so I can fix it.

Why yet another slug engine ?

I started to search for gems providing slug support. I have to say there are really great slug engines out there. However, I couldn't find any slug engine able to work without a database. So I implemented it. Is dead simple.


  1. Avoid duplicated data in your database. You need to take care of the slugs in the case they aren't permanent, by installing ActiveRecord callbacks for updating it. Forgetting installing a callback could mean that you have inconsistent and misleading information (e.g. '/users/23-john-doee' could actually show user 'John Doe' because he updated his profile to fix the typo).

  2. Prettify URL's.

  3. Secure your ID's. Avoid the typical random script that will just increase an ID, and will find out random information about your users/clients.

  4. Save space in database. While the database grows, slugs are also taking its part in consuming space.

  5. Compatible with other slug engines. You can still use friendly_id wherever you want (or any other slug engine). You can decide on which models you want to use Inferred Slugs, and avoid saving slugs of that particular model in the database.


  1. You cannot set permalinks with this slugs. Since the slug itself is inferred from the data of the record, you cannot relay on that (unless that field is immutable by design on your application) to provide permalinks.

  2. The ID is shown. Resources on the location bar is of the form '3-test-foo'. Given the design, there is no way of removing it.


  1. Add 'inferred_slug' to your Gemfile.

  2. Optional: run 'rails g inferred_slug:install'

The optional step will include slugs on all your models automatically, by installing an initializer that adds slugs to ActiveRecord::Base, superclass of all your models. Thus, all your models magically have slugs.

If you want to specify slugs on a per-model basis, you can skip step 2 (or delete the config/initializers/slug.rb file if you already ran it), and explicitly include InferredSlug::Slug on the models that you want to have slugs.

How it works

Right now is very simple. It will check if your model contains a 'name' column, and in that case, the resource will automatically be called '#{id}-#{name}'. Now let's suppose you have a Post model that instead of name has a title column, and you want to use that as the slug:

class Post < ActiveRecord::Base
  include InferredSlug::Slug # Only necessary if the initializer isn't installed

  def slug

Working with it

You have now two methods that will allow you to search by slugs:

  1. find_by_slug

  2. find_by_slug!

They are finder methods, so they are also in collections. Examples:

  1. Client.find_by_slug '1-john-doe'

  2. Client.first.users.find_by_slug '54-alice-smith'