How to integrate with multiple external services without letting any of them leak into your business logic: one port, multiple adapters, and two ways to choose which adapter should run.
Getting rid of the arrow anti-pattern and writing business rules as a flat flow: guard clauses, early return, and how to test them with unit tests.
An email queue that accepts work with a single INSERT and lets workers handle it reliably: the data model, the race conditions, why exactly-once does not exist, and how to choose between DB polling and a broker.
Splitting the seat, no-fly, passport, amount and promo checks of an airline booking into independent links of a chain, with Spring Boot.
The Facade Pattern does not remove complex subsystems. It hides them behind one door. Let’s see it in Spring Boot with a real airline booking scenario.
Using the Mediator Pattern with Zustand on a checkout screen, where country, shipping, payment and coupon components all affect each other.
You load the main records with one query, then run one more query for every relation. How the N+1 problem happens, how to notice it, and which fix to use when.
One page that renders every feature this site supports, so I can see what a thing looks like before deciding to use it.