Ruby on Rails email user when a new record with their preference is added

In my Ruby on Rails application I am creating a cinema site. A user can save their favourite actor in the preferences table, and what I am trying to do is get it so that if a new film is added that has this actor, then all users with that actor as their favourite are emailed the film's details.

I have a email system already working where the user is emailed to confirm that they have successfully registered.

The problem I am having is that I need to retrieve the actors added in a new film record through the controller and if this matches the user's preference then email them. But I am struggling on how to inspect the film's params before saving it.

So far I have done the following in application controller to find user emails where they have the actor Benedict Cumberbatch as their favourite:

def actor_user
    actor = "Benedict Cumberbatch"
    user = Perference.where(actor: actor).pluck(:user_id)
    User.where(id: user).pluck(:email)
end

The problem with this as well is that the actor is hardcoded, whereas what I want to do is extract the names of the film's three actors from the film actors and inspect through these.

Films_controller:

def create
    @film = Film.new(film_params)
    if @film.save
        redirect_to @film
    else
        render 'new'
    end
end

User_Mailer.rb

class UserMailer < ApplicationMailer
  default from: 'no-reply@thorcinemas.com'

  def welcome_email(user)
    @user = user
    @url  = 'http://localhost:3000/users/login'
    # mail(to: @user.email, subject: 'Welcome to My Awesome Site')
    mail(to: @user.email, subject: 'Welcome to My Awesome Site')
  end
end

application_mailer:

class ApplicationMailer < ActionMailer::Base
  #default sender: "ben@thorcinemas.com"
  default from: "ben@thorcinemas.com"
  layout 'mailer'
end

config/environments/development.rb:

config.action_mailer.delivery_method = :smtp
# SMTP settings for gmail
config.action_mailer.smtp_settings = {
 :address              => "smtp.gmail.com",
 :port                 => 587,
 :user_name            => ENV['my_email
 :password             => ENV['my_password'],
 :authentication       => "plain",
:enable_starttls_auto => true
}

Can someone please help. I understand that I will need a new email (as at the minute I only have welcome_email.html.erb), so will need to these in due course.

This is the schema:

  create_table "films", force: :cascade do |t|
     t.string   "title"
     t.string   "synopsis"
     t.string   "director"
     t.string   "cast1"
     t.string   "cast2"
     t.string   "cast3"
     t.date     "release_date"
     t.string   "warnings"
     t.datetime "created_at",     null: false
     t.datetime "updated_at",     null: false
     t.string   "image_url"
     t.string   "certificate_id"
     t.integer  "category_id"
     t.integer  "hours"
     t.integer  "minutes"
     t.string   "video_url"
   end

   create_table "perferences", force: :cascade do |t|
     t.integer  "user_id"
     t.integer  "category_id"
     t.datetime "created_at",  null: false
     t.datetime "updated_at",  null: false
     t.text     "colour"
     t.text     "actor"
   end

 create_table "users", force: :cascade do |t|
    t.string   "password_digest"
    t.string   "role"
    t.datetime "created_at",      null: false
    t.datetime "updated_at",      null: false
    t.string   "first_name"
    t.string   "last_name"
    t.string   "house_no"
    t.string   "street"
    t.string   "town"
    t.string   "postcode"
    t.string   "email"
    t.date     "date_of_birth"
  end

I understand that I have broken best practices by having actor1, actor2, actor3, in the films table rather than having an actors table, but for the purpose of this question, please ignore this.