CodeSnips

ruby

class CreateInventoryReservations < ActiveRecord::Migration[7.1]
  def change
    create_table :inventory_items do |t|
      t.string  :sku, null: false
      t.integer :quantity_on_hand,  null: false, default: 0
      t.integer :quantity_reserved, null: false, default: 0

Transactional “Reserve Inventory” with SELECT … FOR UPDATE

rails activerecord transactions

by codesnips 3 tabs

ruby

class DiscountCode < ApplicationRecord
  has_many :redemptions, dependent: :destroy

  enum discount_type: { percentage: 0, fixed: 1 }

  validates :code, presence: true, uniqueness: { case_sensitive: false }

Redeem Discount Codes in Rails with a Locking Service and Row-Level Guards

rails activerecord discounts

by codesnips 4 tabs

ruby

class CreateAccountsAndLedger < ActiveRecord::Migration[7.1]
  def change
    create_table :accounts do |t|
      t.string :name, null: false
      t.string :currency, null: false, default: "USD"
      t.bigint :balance_cents, null: false, default: 0

Atomic Account Transfers in Rails With Row Locks and a Balance Service

rails postgres transactions

by codesnips 4 tabs

python

import errno
import fcntl
import os
import time

File-Based Locking to Prevent Concurrent Cron Job Runs in Python

locking concurrency fcntl

by codesnips 3 tabs

sql

-- Step 1: add the column nullable, no default.
-- Catalog-only change in Postgres 11+, returns instantly.
ALTER TABLE orders
  ADD COLUMN currency text;

-- Optional: keep the lock attempt bounded so a long-running

SQL migration safety: add column nullable, backfill, then constrain

postgres migrations reliability

by codesnips 3 tabs