simple-mongoid-slug.rb

module SimpleMongoidSlug
  extend ActiveSupport::Concern

  included do
    cattr_accessor :slug_scope, :slug_field
  end

  module ClassMethods
    def slug(*field)
      options = field.extract_options!
      self.slug_scope = options[:scope]
      self.slug_field = field.first

      # Add the slug field to the model
      field(:slug, type: String)

      # Add index info to the model
      if slug_scope
        scope_key = (metadata = self.reflect_on_association(slug_scope)) ? metadata.key : slug_scope
        index({scope_key => 1, slug: 1}, {unique: true, sparse: true})
      else
        index({slug: 1}, {unique: true, sparse: true})
      end

      # Generate slugs automatically
      set_callback :validation, :before, :build_slug, if: :slug_should_be_rebuilt?
    end
  end

  def slug_should_be_rebuilt?
    new_record? || attribute_changed?(self.slug_field.to_s)
  end

  def build_slug
    self.slug = generate_unique_slug
  end

  def generate_unique_slug
    # Start with a base slug
    unique_slug = self.send(self.slug_field).parameterize

    # Find all existing blah, blah-n slugs
    conditions = {}
    conditions[:slug] = /^#{Regexp.escape(unique_slug)}(?:-(\d+))?$/
    conditions[:_id.ne] = self._id
    existing_slugs = uniqueness_scope.unscoped.where(conditions).only(:slug).map &:slug

    # Add suffix until unique
    slug_suffix = 1
    while existing_slugs.include?(unique_slug)
      unique_slug = "#{unique_slug}-#{slug_suffix}"
      slug_suffix += 1
    end

    unique_slug
  end

  def uniqueness_scope
    if slug_scope
      metadata = reflect_on_association(slug_scope)
      parent = self.send(metadata.name)
      inverse = metadata.inverse_of || collection_name
      parent.respond_to?(inverse) ? parent.send(inverse) : self.class
    else
      self.class
    end
  end
end