Problem that the attribute of User model becomes nil in ActionMailer

Execution environment

• Rails 6.0.3

What I was trying to do

Send an email when creating a new user

app/controllers/users_controller.rb

class UsersController < ApplicationController
  def create
    @user = User.new(user_params)
    if @user.save
      UserMailer.activation(@user).deliver_later
      redirect_to root_url
    else
      render "new"
    end
  end
end

Pass the user object

app/mailers/user_mailer.rb

class UserMailer < ApplicationMailer
  def activation(user)
    @user = user
    mail(to: @user.email, subject: 'Please activate your account')
  end
end

Send activation token

app/views/user_mailer/activation.html.slim

p= "Hello,#{@user.name}Mr."

Click the p link to activate your account
= link_to "Activate account", edit_account_activation_url(@user.activation_token, email: @user.email)

Activation token is created at user create

app/models/user.rb

class User < ApplicationRecord
  attr_accessor :activation_token
  before_create :create_activation_digest

  private
    def create_activation_digest
      self.activation_token = SecureRandom.urlsafe_base64
      self.activation_digest = BCrypt::Password.create(activation_token)
    end
end

Error that occurred

ActionView::Template::Error (No route matches {:action=>"edit", :controller=>"account_activations", :email=>"address", :id=>nil}, possible unmatched constraints: [:id]):

@ user.activation_token has become nil

Investigate the error

If you look at @ user.object_id and @ user.activation_token

44860
"I2BCoTsomoNhqNF0q_zRKw"
[ActiveJob] -----

  User Load (0.8ms)  SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2  [["id", 70], ["LIMIT", 1]]

[ActiveJob] -----
44980
nil

It's a different object and ʻactivation_token is also nil`!

Cause of error

deliver_later

If you send an email with deliver_later, you will see that it is looking for a user from the database before running ʻUserMailer`.

  User Load (0.8ms)  SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2  [["id", 70], ["LIMIT", 1]]

The value of the ʻactivation_token attribute cannot be referenced in the ʻuser object obtained from the database after saving because it only has the @ user when @ user.save is executed.

Solution

Use deliver_now

app/controllers/users_controller.rb

class UsersController < ApplicationController
  def create
    @user = User.new(user_params)
    if @user.save
      UserMailer.activation(@user).deliver_now
      redirect_to root_url
    else
      render "new"
    end
  end
end

If you send with deliver_now, the argument will be passed as it is, so it succeeds!

37900
"2kQLrYZjinTiJFKE3jdPqQ"
37900
"2kQLrYZjinTiJFKE3jdPqQ"

Summary of deliver_now and deliver_later

deliver_now Send an email immediately

deliver_late ʻSend an email later using Active Job`

https://railsguides.jp/active_job_basics.html#action-mailer

https://api.rubyonrails.org/classes/ActionMailer/MessageDelivery.html#method-i-deliver_later

• I am a beginner. If you make a mistake, correct it.