module FriendlyId::Slugged

@guide begin

## 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 characters, 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 {FriendlyId::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 {FriendlyId::Slugged::Configuration#slug_column 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 [parameterize](api.rubyonrails.org/classes/ActiveSupport/Inflector.html#method-i-parameterize) 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"

#### Column or Method?

FriendlyId always uses a method as the basis of the slug text - not a column. At 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
  extend FriendlyId
  friendly_id :name_and_location, use: :slugged

  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"

FriendlyId refers to this internally as the “base” method.

#### Uniqueness

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

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

car.friendly_id #=> "peugeot-206"
car2.friendly_id #=> "peugeot-206-f9f3789a-daec-4156-af1d-fab81aa16ee5"

Previous versions of FriendlyId appended a numeric sequence to make slugs unique, but this was removed to simplify using FriendlyId in concurrent code.

#### Candidates

Since UUIDs are ugly, FriendlyId provides a “slug candidates” functionality to let you specify alternate slugs to use in the event the one you want to use is already taken. For example:

class Restaurant < ActiveRecord::Base
  extend FriendlyId
  friendly_id :slug_candidates, use: :slugged

  # Try building a slug based on the following fields in
  # increasing order of specificity.
  def slug_candidates
    [
      :name,
      [:name, :city],
      [:name, :street, :city],
      [:name, :street_number, :street, :city]
    ]
  end
end

r1 = Restaurant.create! name: 'Plaza Diner', city: 'New Paltz'
r2 = Restaurant.create! name: 'Plaza Diner', city: 'Kingston'

r1.friendly_id  #=> 'plaza-diner'
r2.friendly_id  #=> 'plaza-diner-kingston'

To use candidates, make your FriendlyId base method return an array. The method need not be named `slug_candidates`; it can be anything you want. The array may contain any combination of symbols, strings, procs or lambdas and will be evaluated lazily and in order. If you include symbols, FriendlyId will invoke a method on your model class with the same name. Strings will be interpreted literally. Procs and lambdas will be called and their return values used as the basis of the friendly id. If none of the candidates can generate a unique slug, then FriendlyId will append a UUID to the first candidate as a last resort.

#### Sequence Separator

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

You can change this with the {FriendlyId::Slugged::Configuration#sequence_separator sequence_separator} configuration option.

#### Providing Your Own Slug Processing Method

You can override {FriendlyId::Slugged#normalize_friendly_id} in your model for total control over the slug format. It will be invoked for any generated slug, whether for a single slug or for slug candidates.

#### Deciding When to Generate New Slugs

As of FriendlyId 5.0, slugs are only generated when the `slug` field is nil. If you want a slug to be regenerated,set the slug field to nil:

restaurant.friendly_id # joes-diner
restaurant.name = "The Plaza Diner"
restaurant.save!
restaurant.friendly_id # joes-diner
restaurant.slug = nil
restaurant.save!
restaurant.friendly_id # the-plaza-diner

You can also override the {FriendlyId::Slugged#should_generate_new_friendly_id?} method, which lets you control exactly when new friendly ids are set:

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

  def should_generate_new_friendly_id?
    title_changed?
  end
end

If you want to extend the default behavior but add your own conditions, don't forget to invoke `super` from your implementation:

class Category < ActiveRecord::Base
  extend FriendlyId
  friendly_id :name, :use => :slugged

  def should_generate_new_friendly_id?
    name_changed? || super
  end
end

#### Locale-specific Transliterations

Active Support's `parameterize` uses [transliterate](api.rubyonrails.org/classes/ActiveSupport/Inflector.html#method-i-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

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](github.com/norman/friendly_id/issues/185) for discussion.

@guide end

Public Class Methods

included(model_class) click to toggle source

Sets up behavior and configuration options for FriendlyId's slugging feature.

# File lib/friendly_id/slugged.rb, line 241
def self.included(model_class)
  model_class.friendly_id_config.instance_eval do
    self.class.send :include, Configuration
    self.slug_generator_class ||= SlugGenerator
    defaults[:slug_column] ||= "slug"
    defaults[:sequence_separator] ||= "-"
  end
  model_class.before_validation :set_slug
  model_class.before_save :set_slug
  model_class.after_validation :unset_slug_if_invalid
end

Public Instance Methods

normalize_friendly_id(value) click to toggle source

Process the given value to make it suitable for use as a slug.

This method is not intended to be invoked directly; FriendlyId uses it internally to process strings into slugs.

However, if FriendlyId's default slug generation doesn't suit your needs, you can override this method in your model class to control exactly how slugs are generated.

### Example

class Person < ActiveRecord::Base
  extend FriendlyId
  friendly_id :name_and_location

  def name_and_location
    "#{name} from #{location}"
  end

  # Use default slug, but upper case and with underscores
  def normalize_friendly_id(string)
    super.upcase.gsub("-", "_")
  end
end

bob = Person.create! :name => "Bob Smith", :location => "New York City"
bob.friendly_id #=> "BOB_SMITH_FROM_NEW_YORK_CITY"

### More Resources

You might want to look into Babosa, which is the slugging library used by FriendlyId prior to version 4, which offers some specialized functionality missing from Active Support.

@param [#to_s] value The value used as the basis of the slug. @return The candidate slug text, without a sequence.

# File lib/friendly_id/slugged.rb, line 289
def normalize_friendly_id(value)
  value = value.to_s.parameterize
  value = value[0...friendly_id_config.slug_limit] if friendly_id_config.slug_limit
  value
end
resolve_friendly_id_conflict(candidates) click to toggle source

Public: Resolve conflicts.

This method adds UUID to first candidate and truncates (if `slug_limit` is set).

Examples:

resolve_friendly_id_conflict(['12345'])
# => '12345-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'

FriendlyId.defaults { |config| config.slug_limit = 40 }
resolve_friendly_id_conflict(['12345'])
# => '123-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'

candidates - the Array with candidates.

Returns the String with new slug.

# File lib/friendly_id/slugged.rb, line 319
def resolve_friendly_id_conflict(candidates)
  uuid = SecureRandom.uuid
  [
    apply_slug_limit(candidates.first, uuid),
    uuid
  ].compact.join(friendly_id_config.sequence_separator)
end
should_generate_new_friendly_id?() click to toggle source

Whether to generate a new slug.

You can override this method in your model if, for example, you only want slugs to be generated once, and then never updated.

# File lib/friendly_id/slugged.rb, line 299
def should_generate_new_friendly_id?
  send(friendly_id_config.slug_column).nil? && !send(friendly_id_config.base).nil?
end

Private Instance Methods

apply_slug_limit(candidate, uuid) click to toggle source

Private: Apply slug limit to candidate.

candidate - the String with candidate. uuid - the String with UUID.

Return the String with truncated candidate.

# File lib/friendly_id/slugged.rb, line 333
def apply_slug_limit(candidate, uuid)
  return candidate unless candidate && friendly_id_config.slug_limit

  candidate[0...candidate_limit(uuid)]
end
candidate_limit(uuid) click to toggle source

Private: Get max length of candidate.

uuid - the String with UUID.

Returns the Integer with max length.

# File lib/friendly_id/slugged.rb, line 345
def candidate_limit(uuid)
  [
    friendly_id_config.slug_limit - uuid.size - friendly_id_config.sequence_separator.size,
    0
  ].max
end
scope_for_slug_generator() click to toggle source
# File lib/friendly_id/slugged.rb, line 363
def scope_for_slug_generator
  scope = self.class.base_class.unscoped
  scope = scope.friendly unless scope.respond_to?(:exists_by_friendly_id?)
  primary_key_name = self.class.primary_key
  scope.where(self.class.base_class.arel_table[primary_key_name].not_eq(send(primary_key_name)))
end
set_slug(normalized_slug = nil) click to toggle source

Sets the slug.

# File lib/friendly_id/slugged.rb, line 354
def set_slug(normalized_slug = nil)
  if should_generate_new_friendly_id?
    candidates = FriendlyId::Candidates.new(self, normalized_slug || send(friendly_id_config.base))
    slug = slug_generator.generate(candidates) || resolve_friendly_id_conflict(candidates)
    send "#{friendly_id_config.slug_column}=", slug
  end
end
slug_generator() click to toggle source
# File lib/friendly_id/slugged.rb, line 371
def slug_generator
  friendly_id_config.slug_generator_class.new(scope_for_slug_generator, friendly_id_config)
end
unset_slug_if_invalid() click to toggle source
# File lib/friendly_id/slugged.rb, line 376
def unset_slug_if_invalid
  if errors.key?(friendly_id_config.query_field) && attribute_changed?(friendly_id_config.query_field.to_s)
    diff = changes[friendly_id_config.query_field]
    send "#{friendly_id_config.slug_column}=", diff.first
  end
end