Intermediate code explainers

python

from datetime import datetime
from fastapi import APIRouter, Depends, HTTPException, status
from pydantic import BaseModel, ConfigDict, EmailStr
from sqlalchemy.orm import Session

Building a users router in FastAPI

routing serialization dependency-injection

Intermediate 7 steps

javascript

import { NextResponse } from 'next/server'
 
const UPSTREAM = 'https://api.exchangerate.host/latest'

A cached exchange-rate proxy in Next.js

route-handler caching revalidation

Intermediate 7 steps

ruby

class Subscription < ApplicationRecord
  belongs_to :account
 
  enum :status, {

Modeling subscription lifecycle in Rails

enums scopes state-management

Intermediate 8 steps

typescript

type Event = Record<string, unknown>;
 
interface BatcherOptions {
  endpoint: string;

Batching analytics events in TypeScript

batching buffering async

Intermediate 8 steps

php

<?php
 
namespace App\Console\Commands;

Streaming CSV imports in Laravel

lazy-evaluation generators batch-processing

Intermediate 7 steps

java

@Service
public class OrderCheckoutService {
 
    private final OrderRepository orderRepository;

How @Transactional guards a Spring checkout

dependency-injection transactions atomicity

Intermediate 6 steps

python

import json
from dataclasses import dataclass, field, asdict
from datetime import datetime
from typing import Any

JSON round-tripping with Python dataclasses

dataclasses serialization json

Intermediate 6 steps

javascript

const logger = require('./logger');
 
class AppError extends Error {
  constructor(message, statusCode = 500, details = null) {

Centralized error handling in Express

error-handling middleware custom-errors

Intermediate 8 steps

ruby

class InactiveAccountCleanup
  BATCH_SIZE = 500
  INACTIVITY_THRESHOLD = 18.months

Batch-processing dormant users in Rails

batch-processing activerecord service-object

Intermediate 9 steps

typescript

import { Injectable } from '@angular/core';
import { PreloadingStrategy, Route, Routes, RouterModule } from '@angular/router';
import { NgModule } from '@angular/core';
import { Observable, of, timer } from 'rxjs';

A custom preloading strategy in Angular

lazy-loading preloading rxjs

Intermediate 7 steps

go

package middleware
 
import (
	"compress/gzip"

How gzip response compression works in Gin

middleware compression http

Intermediate 8 steps

php

<?php
 
namespace App\Services;

Resilient HTTP retries with Laravel's client

http-client retry-logic error-handling

Intermediate 7 steps

java

@Service
public class OrderMetricsService {
 
    private final MeterRegistry registry;

Instrumenting orders with Micrometer in Spring

metrics micrometer observability

Intermediate 8 steps

rust

use std::fs::File;
use std::io::{self, BufWriter};
use std::path::Path;

Serializing config to JSON in Rust

serialization serde file-io

Intermediate 7 steps

python

import re
 
from django.core.exceptions import ValidationError
from django.core.validators import RegexValidator

Building a deconstructible validator in Django

validation regex deconstructible

Intermediate 7 steps

javascript

const formatters = new Map();
 
function getFormatter(locale, currency) {
  const key = `${locale}:${currency}`;

Caching Intl.NumberFormat for currency formatting

memoization internationalization caching

Intermediate 8 steps

ruby

class ArticleSerializer < ActiveModel::Serializer
  attributes :id, :title, :slug, :excerpt, :reading_time, :published_at, :url
 
  belongs_to :author, serializer: UserSerializer

Shaping API output with ActiveModel::Serializer in Rails

serialization json api computed attributes

Intermediate 9 steps

typescript

import { Processor, WorkerHost, OnWorkerEvent } from '@nestjs/bullmq';
import { Logger } from '@nestjs/common';
import { Job } from 'bullmq';
import { MailerService } from '../mailer/mailer.service';

Processing background email jobs in NestJS

job-queue background-processing dependency-injection

Intermediate 7 steps