Ruby on Rails code explainers

class DashboardMetrics
  CACHE_TTL = 15.minutes
 
  def initialize(account)

class Article < ApplicationRecord
  belongs_to :author, class_name: "User"
  has_many :taggings, dependent: :destroy
  has_many :tags, through: :taggings

class CreateOrderItems < ActiveRecord::Migration[7.1]
  def change
    create_table :order_items do |t|
      t.references :order, null: false, foreign_key: { on_delete: :cascade }

class Registration < ApplicationRecord
  belongs_to :event
 
  validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }

class NewCommentNotifier < ApplicationNotifier
  deliver_by :database
 
  deliver_by :email do |config|

class DocumentsController < ApplicationController
  before_action :authenticate_user!
  before_action :set_document
 

class ApplicationJob < ActiveJob::Base
  retry_on ActiveRecord::Deadlocked, wait: 5.seconds, attempts: 3
  discard_on ActiveJob::DeserializationError
 

class PasswordResetsController < ApplicationController
  RESET_PURPOSE = :password_reset
  RESET_EXPIRY = 15.minutes
 

module ProductsHelper
  def cached_product_row(product)
    cache [product, current_user.role] do
      render partial: "products/row", locals: { product: product }

class DigestMailer < ApplicationMailer
  default from: "notifications@example.com"
 
  def weekly_digest(user)

class OrdersController < ApplicationController
  rescue_from ActiveRecord::RecordNotUnique, with: :handle_duplicate_submission
 
  def create

class InventoryItem < ApplicationRecord
  belongs_to :warehouse
 
  validates :quantity, numericality: { greater_than_or_equal_to: 0 }

class PaymentMethod < ApplicationRecord
  belongs_to :account
 
  encrypts :card_number, deterministic: false

class User < ApplicationRecord
  has_secure_password
 
  normalizes :email, with: ->(email) { email.strip.downcase }

class Account < ApplicationRecord
  has_many :projects, dependent: :destroy_async
  has_many :memberships, dependent: :destroy_async
  has_many :invoices, dependent: :restrict_with_error

require "csv"
 
class Api::V1::ProductImportsController < Api::V1::BaseController
  MAX_ROWS = 10_000

class HealthController < ApplicationController
  skip_before_action :authenticate_user!, raise: false
  skip_forgery_protection
 

module Instrumentation
  module Timing
    def self.[](*method_names)
      Module.new do