Module: FriendlyId::Slugged

Slugged Models

FriendlyId can use a separate column to store slugs for models which require some text processing.

For example, blog applications typically use a post title to provide the basis of a search engine friendly URL. Such identifiers typically lack uppercase characters, use ASCII to approximate UTF-8 character, and strip out other characters which may make them aesthetically unappealing or error-prone when used in a URL.

class Post < ActiveRecord::Base
  extend FriendlyId
  friendly_id :title, :use => :slugged
end

@post = Post.create(:title => "This is the first post!")
@post.friendly_id   # returns "this-is-the-first-post"
redirect_to @post   # the URL will be /posts/this-is-the-first-post

In general, use slugs by default unless you know for sure you don't need them. To activate the slugging functionality, use the Slugged module.

FriendlyId will generate slugs from a method or column that you specify, and store them in a field in your model. By default, this field must be named :slug, though you may change this using the slug_column configuration option. You should add an index to this column, and in most cases, make it unique. You may also wish to constrain it to NOT NULL, but this depends on your app's behavior and requirements.

Example Setup

# your model
class Post < ActiveRecord::Base
  extend FriendlyId
  friendly_id :title, :use => :slugged
  validates_presence_of :title, :slug, :body
end

# a migration
class CreatePosts < ActiveRecord::Migration
  def self.up
    create_table :posts do |t|
      t.string :title, :null => false
      t.string :slug, :null => false
      t.text :body
    end

    add_index :posts, :slug, :unique => true
  end

  def self.down
    drop_table :posts
  end
end

Working With Slugs

Formatting

By default, FriendlyId uses Active Support's paramaterize method to create slugs. This method will intelligently replace spaces with dashes, and Unicode Latin characters with ASCII approximations:

movie = Movie.create! :title => "Der Preis fürs Überleben"
movie.slug #=> "der-preis-furs-uberleben"

Uniqueness

When you try to insert a record that would generate a duplicate friendly id, FriendlyId will append a sequence to the generated slug to ensure uniqueness:

car = Car.create :title => "Peugot 206"
car2 = Car.create :title => "Peugot 206"

car.friendly_id #=> "peugot-206"
car2.friendly_id #=> "peugot-206--2"

Sequence Separator - The Two Dashes

By default, FriendlyId uses two dashes to separate the slug from a sequence.

You can change this with the sequence_separator configuration option.

Column or Method?

FriendlyId always uses a method as the basis of the slug text - not a column. It first glance, this may sound confusing, but remember that Active Record provides methods for each column in a model's associated table, and that's what FriendlyId uses.

Here's an example of a class that uses a custom method to generate the slug:

class Person < ActiveRecord::Base
  friendly_id :name_and_location
  def name_and_location
    "#{name} from #{location}"
  end
end

bob = Person.create! :name => "Bob Smith", :location => "New York City"
bob.friendly_id #=> "bob-smith-from-new-york-city"

Providing Your Own Slug Processing Method

You can override #normalize_friendly_id in your model for total control over the slug format.

Deciding When to Generate New Slugs

Overriding #should_generate_new_friendly_id? lets you control whether new friendly ids are created when a model is updated. For example, if you only want to generate slugs once and then treat them as read-only:

class Post < ActiveRecord::Base
  extend FriendlyId
  friendly_id :title, :use => :slugged

  def should_generate_new_friendly_id?
    new_record?
  end
end

post = Post.create!(:title => "Hello world!")
post.slug #=> "hello-world"
post.title = "Hello there, world!"
post.save!
post.slug #=> "hello-world"

Locale-specific Transliterations

Active Support's parameterize uses transliterate, which in turn can use I18n's transliteration rules to consider the current locale when replacing Latin characters:

# config/locales/de.yml
de:
  i18n:
    transliterate:
      rule:
        ü: "ue"
        ö: "oe"
        etc...

movie = Movie.create! :title => "Der Preis fürs Überleben"
movie.slug #=> "der-preis-fuers-ueberleben"

This functionality was in fact taken from earlier versions of FriendlyId.

Gotchas: Common Problems

Slugs That Begin With Numbers

Ruby's `to_i` function casts strings to integers in such a way that 23abc.to_i returns 23. Because FriendlyId falls back to finding by numeric id, this means that if you attempt to find a record with a non-existant slug, and that slug begins with a number, your find will probably return the wrong record.

There are two fairly simple ways to avoid this:

• Use validations to ensure that slugs don't begin with numbers.

• Use explicit finders like find_by_id to always find by the numeric id, or find_by_slug to always find using the friendly id.

Concurrency Issues

FriendlyId uses a before_validation callback to generate and set the slug. This means that if you create two model instances before saving them, it's possible they will generate the same slug, and the second save will fail.

This can happen in two fairly normal cases: the first, when a model using nested attributes creates more than one record for a model that uses friendly_id. The second, in concurrent code, either in threads or multiple processes.

To solve the nested attributes issue, I recommend simply avoiding them when creating more than one nested record for a model that uses FriendlyId. See this Github issue for discussion.

To solve the concurrency issue, I recommend locking the model's table against inserts while when saving the record. See this Github issue for discussion.