after_removing_callbacks_model.rb

class Customer < ActiveRecord::Base
    has_one :auto_created, dependent: :destroy
    
    def self.register(params)
        new(params).tap do |customer|
            customer.save!
            customer.send_welcome_email
        end
    end
        
    def self.auto_create(params)
        new(params).tap do |customer|
            customer.save!
        end
    end
    
    def send_welcome_email
        CustomerMailer.welcome_email(self).deliver
    end
end

I would rename register and auto_create to register! and auto_create! because save! which is called inside may raise an error. What do you think @Killavus ?