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Lessons (6)

• D — Dependency Inversion Principle

  … business logic glued to details js import { MySQLDatabase } from "./mysql.js"; import { SendGridMailer } from "./sendgrid.js"; // ❌ OrderService creates …

• AWS Databases: Choose the Right One

  … managed SQL database RDS runs engines such as PostgreSQL and MySQL while AWS handles hardware, backups, and many …

• 10,000 Users Do Not Need 10,000 Database Connections

  … PostgreSQL traditionally uses a server process per connection; MySQL commonly uses a thread-per-connection model. Those implementation …

• SOLID at a Glance

  … logic / } toExcel() { / Excel logic / } saveToMySql() { const db = new MySqlConnection(); / … / } email() { const smtp = new GmailSmtp(); / … / } } js // ✅ SOLID version class …

• SQL vs NoSQL Databases

  … and SQL is a universal language. Examples: PostgreSQL, MySQL, SQL Server, SQLite (which this very app uses!). ACID …

• Database Indexing & Transactions

  … possible possible Postgres default Repeatable Read ✅ ✅ prevented possible MySQL InnoDB default Serializable ✅ ✅ ✅ prevented Safest, slowest, may need retries …