#migrations code explainers

ruby

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

Enforcing order-item integrity in Rails

migrations foreign-keys validations

Intermediate 7 steps

javascript

const STORAGE_KEY = "app_state";
const CURRENT_VERSION = 3;
 
const migrations = {

Versioned state migrations in localStorage

migrations persistence versioning

Intermediate 9 steps

ruby

class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true, counter_cache: true
  belongs_to :author, class_name: "User"

How polymorphic comments work in Rails

polymorphic-association concerns counter-cache

Intermediate 8 steps

ruby

class CreateCommentsWithCounterCache < ActiveRecord::Migration[7.1]
  def change
    create_table :posts do |t|
      t.string :title, null: false

How counter caches work in Rails

counter-cache migrations associations

Intermediate 6 steps