skinny controller

REFACTORING-Controller.rb

#Let's extract some registration logic out of our controllers into a UserRegistration class. 
#This class should take user_params as arguments to its constructor, 
#which are used to initialize a new User (not create). 
#This newly initialized user should be available as an attr_reader. 
#You'll also want to move the valid_background_check? method 
#into this new class as a private method, we'll use this later to finish creating the User.

class UsersController < ApplicationController
  def create
    @user = User.new(user_params)

    if valid_background_check?
      @user.is_approved = true
    end

    if @user.save
      redirect_to @user
    else
      render :new
    end
  end

  private

  def valid_background_check?
    !!(@user.valid_ssn? || @user.valid_address?)
  end

  def user_params
    params.require(:user).permit(:name, :email, :ssn, :address)
  end
end


class UserRegistration

  private
  # private methods go here
end

step1.rb

class UsersController < ApplicationController
  
  def create
    registration = UserRegistration.new(user_params)
    @user = registration.user
    if registration.create
      redirect_to @user
    else
      render :new
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :email, :ssn, :address)
  end
end


class UserRegistration
  attr_reader :user
  
  def initialize(params)
    @user = User.new(params)  
  end
  
  def create
    if valid_background_check?
      @user.is_approved = true 
    end
    @user.save
  end
  private
  # private methods go here
  def valid_background_check?
    !!(@user.valid_ssn? || @user.valid_address?)
  end

end

in line 5 of second file, how does "registration.user' know which user to find? is it just from the attr_reader?