By default, Rails applications build URLs based on the primary key -- the
id column from the database. Imagine we have a
Person model and associated controller. We have a person record for
Bob Martin that has
6. The URL for his show page would be:
But, for aesthetic or SEO purposes, we want Bob's name in the URL. The last segment, the
6 here, is called the "slug". Let's look at a few ways to implement better slugs.
The simplest approach is to override the
to_param method in the
Person model. Whenever we call a route helper like this:
Rails will call
to_param to convert the object to a slug for the URL. If your model does not define this method then it will use the implementation in
ActiveRecord::Base which just returns the
For this method to succeed, it's critical that all links use the
ActiveRecord object rather than calling
id. Don't ever do this:
person_path(@person.id) # Bad!
Instead, always pass the object:
Instead, in the model, we can override
to_param to include a parameterized version of the person's name:
class Person < ActiveRecord::Base def to_param [id, name.parameterize].join("-") end end
For our user
Bob Martin with
6, this will generate a slug
6-bob_martin. The full URL would be:
parameterize method from
ActiveSupport will deal with converting any characters that aren't valid for a URL.
What do we need to change about our finders? Nothing! When we call
Person.find(x), the parameter
x is converted to an integer to perform the SQL lookup. Check out how
to_i deals with strings which have a mix of letters and numbers:
> "1".to_i # => 1 > "1-with-words".to_i # => 1 > "1-2345".to_i # => 1 > "6-bob-martin".to_i # => 6
to_i method will stop interpreting the string as soon as it hits a non-digit. Since our implementation of
to_param always has the
id at the front followed by a hyphen, it will always do lookups based on just the
id and discard the rest of the slug.
We've added content to the slug which will improve SEO and make our URLs more readable.
One limitation is that the users cannot manipulate the URL in any meaningful way. Knowing the url
6-bob-martin doesn't allow you to guess the url
7-russ-olsen, you still need to know the ID.
And the numeric ID is still in the URL. If this is something you want to obfuscate, then the simple scheme doesn't help.
Sometimes you want to get away from the ID all together and use another attribute in the database for lookup. Imagine we have a
Tag object that has a
name column. The name would be something like
Creating links can again override
class Tag < ActiveRecord::Base validates_uniqueness_of :name def to_param name end end
Now when we call
tag_path(@tag) we'd get a URL like
The lookup is harder, though. When a request comes in to
ruby will be stored in
params[:id]. A typical controller will call
Tag.find("ruby"), and it will fail.
Instead, we can modify the controller to
Tag.find_by_name(params[:id]). It will work, but it's bad object-oriented design. We're breaking the encapsulation of the
The DRY Principle says that a piece of knowledge should have a single representation in a system. In this implementation of tags, the idea of "A tag can be found by its name" has now been represented in the
to_param of the model and the controller lookup. That's a maintenance headache.
In our model we could define a custom finder:
class Tag < ActiveRecord::Base validates_uniqueness_of :name def to_param name end def self.find_by_param(input) find_by_name(input) end end
Then in the controller call
Tag.find_by_param(params[:id]). This layer of abstraction means that only the model knows exactly how a
Tag is converted to and from a parameter. The encapsulation is restored.
But we have to remember to use
Tag.find_by_param instead of
Tag.find everywhere. Especially if you're retrofitting the friendly ID onto an existing system, this can be a significant effort.
Instead of implementing the custom finder, we could override the
class Tag < ActiveRecord::Base #... def self.find(input) find_by_name(input) end end
It will work when you pass in a name slug, but will break when a numeric ID is passed in. How could we handle both?
The first temptation is to do some type switching:
class Tag < ActiveRecord::Base #... def self.find(input) if input.is_a?(Integer) super else find_by_name(input) end end end
That'll work, but checking type is very against the Ruby ethos. Writing
is_a? should always make you ask "Is there a better way?"
Yes, based on these facts:
- Databases give the
1to the first record
- Ruby converts strings starting with a letter to
class Tag < ActiveRecord::Base #... def self.find(input) if input.to_i != 0 super else find_by_name(input) end end end
Or, condensed down with a ternary:
class Tag < ActiveRecord::Base #... def self.find(input) input.to_i == 0 ? find_by_name(input) : super end end
Our goal is achieved, but we've introduced a possible bug: if a name starts with a digit it will look like an ID. If it's acceptable to our business domain, we can add a validation that names cannot start with a digit:
class Tag < ActiveRecord::Base #... validates_format_of :name, :without => /^\d/ def self.find(input) input.to_i == 0 ? find_by_name(input) : super end end
Now everything should work great!
Does implementing two additional methods seem like a pain? Or, more seriously, are you going to implement this kind of functionality in multiple models of your application? Then it might be worth checking out the FriendlyID gem: https://github.com/norman/friendly_id
The gem is just about to hit a 4.0 version. As of this writing, you want to use the beta. In your
gem "friendly_id", "~> 4.0.0.beta8"
bundle from the command line.
The minimum configuration in your model is:
class Tag < ActiveRecord::Base extend FriendlyId friendly_id :name end
This will allow you to use the
name column or the
id for lookups using
find, just like we did before.
But the library does a great job of maintaining a dedicated slug column for you. If we were dealing with articles, for instance, we don't want to generate the slug over and over. More importantly, we'll want to store the slug in the database to be queried directly.
The library defaults to a
String column named
slug. If you have that column, you can use the
:slugged option to automatically generate and store the slug:
class Tag < ActiveRecord::Base extend FriendlyId friendly_id :name, :use => :slugged end
You can see it in action here:
> t = Tag.create(:name => "Ruby on Rails") # => #<Tag id: 16, name: "Ruby on Rails", created_at: "2011-09-11 15:42:53", updated_at: "2011-09-11 15:42:53", slug: "ruby-on-rails"> > Tag.find 16 # => #<Tag id: 16, name: "Ruby on Rails", created_at: "2011-09-11 15:42:53", updated_at: "2011-09-11 15:42:53", slug: "ruby-on-rails"> > Tag.find "ruby-on-rails" # => #<Tag id: 16, name: "Ruby on Rails", created_at: "2011-09-11 15:42:53", updated_at: "2011-09-11 15:42:53", slug: "ruby-on-rails"> > t.to_param # => "ruby-on-rails"
We can use
.find with an ID or the slug transparently. When the object is converted to a parameter for links, we'll get the slug with no ID number. We get good encapsulation, easy usage, improved SEO and easy to read URLs.