Allow updating an attribute of a User model only once - ruby-on-rails

Question

An admin account creates a user account, this automatically generates a username determined by the user's first and surname.
Once the username is created I want the user to be able to update it only once - Note: This can be at any time or after multiple logins, but once the username has been changed once it needs to be set in stone.
Using Rails and simple_form. The edit form is below.
= simple_form_for(current_user) do |f|
= f.error_notification
.form-inputs
= f.input :name, required: true, label: 'Name'
= f.input :username, required: true
= f.input :email, required: true
= f.input :password, required: true, placeholder: ("#{#minimum_password_length} characters minimum" if #minimum_password_length)
= f.input :password_confirmation, required: true
.form-actions
= f.button :submit, "Update Profile", class: 'btn btn-primary btn-block btn-lg'
Admin/Users controller.
def create
#user = User.new(user_params)
#user.password = SecureRandom.base64()
nameArray = #user.name.split(' ')
#user.username = nameArray[0][0].downcase + nameArray[-1][0..6].downcase
respond_to do |format|
if #user.save
#user.send_reset_password_instructions
format.html do
redirect_to [:admin, #user],
notice: "#{#user} was successfully created. A confirmation email was sent to: #{#user.email}"
end
else
format.html do
flash[:alert] = "User #{#user} already exists, or you have not filled in all of the required fields."
render :new
end
end
end
end
Thanks in advance.

Answer 1

Add new column to User like :edited
def change
add_column :users, :eited, :boolean, default: false
end
In your model User add calback after_update
class User < ApplicationRecord
after_update :set_edited!
before_update :check_if_edited!
def is_edited?
edited?
end
private
def check_if_edited!
# there you can set the error message or what you want
errors.add(:base, :invalid, message: "Your message")) if edited?
end
def set_edited!
transaction do
self.edited = true
self.save!
end
end
end
In your user controller add restriction to update user if is_edited?
def update
if current_user.is_edited?
// preform action
end
end
P.S. migrate logic to assign attributes to model User
class User < ApplicationRecord
after_create :assign_attributes
private
def assign_attributes
transaction do
self.password = SecureRandom.base64()
name_array = name.split(' ')
self.username = nameArray[0][0].downcase + nameArray[-1][0..6].downcase
self.save!
end
end
end

Answer 2

According to me the best way would be to use call_back in user model:
before_update{|user|
user.write_user_name_changed unless user.created_at == user.updated_at
}
def write_user_name_changed
self.user_name_changed = params[:username]
true
end