Rails: Using friendly_id/slug with column from associated model

I've got Contact model which I want to be slugged (friendly_id gem). By using the user_name column from User model which Contact model belongs to.

class Contact < ApplicationRecord
  belongs_to :user

  extend FriendlyId
  friendly_id self.user.user_name, use: :slugged

But typing Contact.find_each(&:save) in my rails console I get this error:

NoMethodError (undefined method `user' for Contact (call 'Contact.connection' to establish a connection):Class)

How can I use my assosiated model as a slug?

Rails version: 5.2.2 Friendly_id gem: 5.2.4

FriendlyId always uses a method as the basis of the slug text, for your problem above I think you create method for user_name and call related field inside a method

class Contact < ApplicationRecord
  belongs_to :user

  extend FriendlyId
  friendly_id :user_name

  def user_name
    user.user_name
  end
end