How to define nested attributes in rails?

Question

Ruby on Rails

It doesn't reach me how to define attributes in the nested controller or use two controllers in one form if possible (it would be cool)
What do I need: When creating a Post model, if the user is not authorized, register or authenticate him? and create a User model, as well as send an email to subscribers about the creation of a new Post.
How is
the form itself now:
views/posts/new.html.erb

<% resourse.posts.build %>
    <%= form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>
      <%= devise_error_messages! %>
        <%= f.email_field :email, placeholder: "E-mail" %>
        <%= f.password_field :password, placeholder: "password" %>
        <%= f.password_field :password_confirmation, placeholder: "password confirmation" %>
           <%= f.fields_for :posts do |form| %>
           <%= form.text_field :title %>
           <%= form.text_field :content %>
      <%= f.submit "Sign up and create post" %>
    <% end %>
    <%= render "devise/shared/links" %>

User.rb

class User < ActiveRecord::Base
  has_many :posts
  accepts_nested_attributes_for :posts
end

class RegistrationsController < Devise::RegistrationsController 

  def new
    super
  end

  def create
    super
#вот тут я не что делать как определить nested_attributes для posts
  end

Now everything works, saves and so on, but I don't know how to send a letter and how to manipulate nested data, share your experience about GREAT!

Answer 1

I did this, maybe it will come in handy for someone
I filed my RegistrationController which refers to Devise
, and if anyone has a thread more than nested attribustes (I have one),
respectively post = resourse.posts.second and so on

class RegistrationsController < Devise::RegistrationsController

def create
    build_resource(sign_up_params)
    resource_saved = resource.save
    yield resource if block_given?
    if resource_saved
    	if resource.posts.present?
    		post = resource.posts.first
    		flash[:success] = "Поздравляем Ваше сообщение опубликованно!"
    		User.includes(:categories, :roles).references(:categories, :roles).where(categories: {id: post.category_id}, roles: { id: 4 }).pluck(:email).each do |email|
        PostsMailer.delay.deliver_posts_register(email, post)
      end
    	end
      if resource.active_for_authentication?
        set_flash_message :notice, :signed_up if is_flashing_format?
        sign_up(resource_name, resource)
        respond_with resource, location: after_sign_up_path_for(resource)
      else
        set_flash_message :notice, :"signed_up_but_#{resource.inactive_message}" if is_flashing_format?
        expire_data_after_sign_in!
        respond_with resource, location: after_inactive_sign_up_path_for(resource)
      end
    else
      clean_up_passwords resource
      @validatable = devise_mapping.validatable?
      if @validatable
        @minimum_password_length = resource_class.password_length.min
      end
      respond_with resource
    end
  end
end

Answer 2

1. How to send a letter - guides.rubyonrails.org/action_mailer_basics.html
2. There are all sorts of callback methods for checks, for example

after_create do |post|
  post.user.nil?
end