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May 26, 2018

Use slugs in Rails URLs

Rails's default routing scheme is alright. /posts/1, /posts/2, etc. But it's not very good for SEO and it's doesn't look great to users, either. Let's change Rails's config to use a slug that we can define ourselves.

Obviously this can be used for any model. We're just using posts here because it's a common use-case for Rails. I mean just look at this site.

Add the slug column to our table

First we need to generate the migration to add the column to the table, which Rails makes very easy:

$ rails g migration add_slug_to_posts slug:string

Don't migrate it just yet, though. We'll be setting Rails up to search for posts by slug (rather than by id), so we'll also want to add an index to the slug column. For performance.

Make sure you add the highlighted part below:

class AddSlugToPosts < ActiveRecord::Migration[5.0]
  def change
    add_column :posts, :slug, :string
    add_index :posts, :slug, unique: true

Now it's time to migrate.

$ rails db:migrate

Add slugs to existing posts (optional)

It may happen that you've already got posts on your site, all of which now have a nil slug field. Which will create problems. Let's fire up the rails console and add some post hoc slugs.

$ rails c

Once in the console, we'll get all of your posts, iterate over them, and update the slug. In this case we're basing the post's slug off its title (since it presumably has a title).

We're using Rails's parameterize function, which removes non-url-safe characters and adds hyphens where spaces exist. Viz. 'Sample Post No. 1' will become 'sample-post-no-1'

Post.find_each do |post|
    post.update_attributes(slug: post.title.parameterize)

You can swap out the hyphen for something else by passing a hash with the separator key to parameterize. For example: 'Sample Post No. 1'.parameterize(separator: '_') => "sample_post_no_1"

Update the routes

We have to make sure to let Rails know that our routes are going to use the slug rather than the id. Rails, of course, has a simple way of dealing with this:

# routes.rb

resources :posts, param: :slug

Update your model

The model also has to know that we're using a slug instead of id as well. It's a good place to put a couple of methods for making sure that our slugs are all going to the right place in the right shape.

We'll add some validation to make sure that our slugs are unique—no sense in having two posts with the same URL.

We're also going to do a little bit of Ruby's famous monkeypatching to change the built-in to_param method to use our slug when building paths, rather than the default id.

And finally, we're going to monkeypatch the find method to find by slug instead of by id. That way we can run calls like Post.find('sample-post-no-1').

# post.rb

validates :slug, uniqueness: true, presence: true

def to_param

def self.find(input)

Update your controller

Now that our find method is finding by slug, our controller is going to run into a problem. You're probably finding by params[:id], which introduces two problems.

  1. find is expecting a slug, so it's going to choke unless your slug is 1 or 55 or something, but—
  2. You're no longer passing in a params[:id], since in our routes.rb we configured the route to use slug as the param. So params[:id] will always be nil.

The solution: just change the params[:id] to params[:slug]. So:

# posts_controller.rb

def show
    @post = Post.find(params[:slug])
def edit
    @post = Post.find(params[:slug])

def update
    @post = Post.find(params[:slug])

Remember as well to add :slug to your post_params:

# posts_controller.rb

def hike_params
    params.require(:post).permit(:title, :slug, :content)

Bonus round: update your already-indexed pages (optional)

It's possible that Google will have already indexed a couple of your e.g. /posts/1, which are all now 404ing. Which means Webmaster Tools will shortly start yelling at you, which is bad not only for your SEO but also for your self esteem.

You could write up a hash or something to map each of your old id-based post URLs to your new slug-based ones, but I'm lazy and I just redirect them back to the posts index page.

We'll add a route matching for /posts/ followed by any numbers, using Rails's constraints option and matching with a regex. This will catch anything like /posts/123 and /posts/999 but won't catch our new /posts/sample-post-no-1.

Now that I think of it, I actually just covered Rails redirect with regexes like last week.

# routes.rb

get 'posts/:id',   constraints: { id: /[0-9]+/ }, to: redirect('posts', status: 301)

Heads up

One thing we didn't cover here was adding a field to whatever form you're using to add new posts to handle slugs. It's not hard to add a field for a slug; or if you're feeling lazy, you could just write a bit of logic to generate a slug from the title in your posts_controller.rb, e.g.:

@post.slug = @post.title.parameterize


That's really all there is to it. It's a very simple way to make your blog a little bit friendlier to search engi—I mean good old users, flocking in droves to your blog.

The droves of users flocking to my blog