You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: stat.rb
    path of file: ./repos/kitsu-server/app/models
    
    the code of the file until where you have to start completion: class Stat < ApplicationRecord
  belongs_to :user

  validates :type, presence: true, uniqueness: { scope: :user_id }

  # Gets a user-specific instance of a stat, aut
    
  def self.for_user(user)
    Retriable.retriable(on: {
      ActiveRecord::RecordNotUnique => nil,
      ActiveRecord::RecordInvalid => /Type has already been taken/
    }, max_elapsed_time: 30) do
      where(user: user).first_or_initialize(&:recalculate!)
    end
  end