```ruby
class Topic < ActiveRecord::Base
  include ContentIdentifiable
  validate :path_can_be_set_once
  validate :path_format

  has_many :topic_sections, -> { order(position: :asc) }
  has_many :guides, through: :topic_sections

  def ready_to_publish?
    persisted?
  end

  def latest_edition
    self
  end

  def update_type
    'major'
  end

  # TODO: We have topics.path and guides.slug. We should standardise with
  # the most commonly used term in other apps.
  def slug
    path
  end

  def guide_content_ids
    topic_sections.map do |topic_section|
      topic_section.guides.map(&:content_id)
    end.flatten
  end

  private

  def path_can_be_set_once
    if persisted? && path != path_was
      errors.add(:path, "can not be changed")
    end
  end

  def path_format
    if !path.to_s.match(/\A\/service-manual\//)
      errors.add(:path, "must be present and start with '/service-manual/'")
    elsif !path.to_s.match(/\A\/service-manual\/[a-z0-9\-\/]+$/i)
      errors.add(:path, "can only contain letters, numbers and dashes")
    end
  end
end
```

Refactor guide_content_ids to use guides has_many
user
```ruby
class Topic < ActiveRecord::Base
  include ContentIdentifiable
  validate :path_can_be_set_once
  validate :path_format

  has_many :topic_sections, -> { order(position: :asc) }
  has_many :guides, through: :topic_sections

  def ready_to_publish?
    persisted?
  end

  def latest_edition
    self
  end

  def update_type
    'major'
  end

  # TODO: We have topics.path and guides.slug. We should standardise with
  # the most commonly used term in other apps.
  def slug
    path
  end

  def guide_content_ids
    guides.pluck(:content_id).uniq
  end

  private

  def path_can_be_set_once
    if persisted? && path != path_was
      errors.add(:path, "can not be changed")
    end
  end

  def path_format
    if !path.to_s.match(/\A\/service-manual\//)
      errors.add(:path, "must be present and start with '/service-manual/'")
    elsif !path.to_s.match(/\A\/service-manual\/[a-z0-9\-\/]+$/i)
      errors.add(:path, "can only contain letters, numbers and dashes")
    end
  end
end
```
assistant