Code Explainers

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java 
@Configuration
@EnableRedisHttpSession(namespace = "myapp:sessions", maxInactiveIntervalInSeconds = 1800, flushMode = FlushMode.IMMEDIATE)
public class SessionConfig {
 

Backing HTTP sessions with Redis in Spring

session-management redis distributed-state
Intermediate 7 steps
python 
from django.db import models
from django.db.models import Q
from django.conf import settings
 

Enforcing one default address per user in Django

data modeling database constraints partial index
Intermediate 7 steps
javascript 
const express = require('express');
const cookieParser = require('cookie-parser');
 
const router = express.Router();

Remember-me login with signed cookies in Express

authentication signed-cookies sessions
Intermediate 9 steps
ruby 
class SearchController < ApplicationController
  def index
    @query = params[:q].to_s.strip
  end

Live search suggestions in a Rails controller

controllers sql-injection query-building
Intermediate 6 steps
go 
package health
 
import (
	"context"

Building a health check endpoint in Go

health-check context-timeout dependency-probing
Intermediate 8 steps
typescript 
type Handler = (event: KeyboardEvent) => void;
 
interface Binding {
  combo: string;

Building a keyboard shortcut manager in TypeScript

event-handling normalization closures
Intermediate 7 steps
php 
namespace App\Providers;
 
use Illuminate\Database\Eloquent\Model;
use Illuminate\Support\Facades\Log;

Catching N+1 queries with Eloquent strict mode in Laravel

n+1 queries strict mode eager loading
Intermediate 7 steps
java 
public List<User> findUsersByEmailDomain(String domain, int minAge) {
    String sql = """
        SELECT id, username, email, age, created_at
        FROM users

Safe parameterized JDBC queries in Java

jdbc sql-injection prepared-statement
Intermediate 7 steps
python 
from typing import Any
 
_MISSING = object()
 

Recursively diffing two JSON structures

recursion sentinel tree-traversal
Intermediate 8 steps
javascript 
const TOKEN_SPECS = [
  ["comment", /^\/\/[^\n]*|^\/\*[\s\S]*?\*\//],
  ["string", /^"(?:\\.|[^"\\])*"|^'(?:\\.|[^'\\])*'|^`(?:\\.|[^`\\])*`/],
  ["number", /^0[xX][\da-fA-F]+|^\d+(?:\.\d+)?(?:[eE][+-]?\d+)?/],

Building a syntax highlighter tokenizer

tokenizer regular-expressions lexing
Intermediate 8 steps
javascript 
export async function compressImage(file, { maxWidth = 1600, maxHeight = 1600, quality = 0.8, mimeType = 'image/jpeg' } = {}) {
  const bitmap = await createImageBitmap(file);
 
  let { width, height } = bitmap;

Compressing images in the browser with canvas

canvas image-processing promises
Intermediate 7 steps
go 
package email
 
import (
	"errors"

Normalizing and deduping email addresses in Go

validation normalization deduplication
Intermediate 8 steps
java 
@Configuration
@EnableBatchProcessing
public class CustomerImportJobConfig {
 

How a chunk-based CSV import job works in Spring

batch-processing etl csv-parsing
Intermediate 9 steps
ruby 
class TasksController < ApplicationController
  before_action :set_project
 
  def reorder

Bulk task reordering with upsert_all in Rails

bulk-update upsert authorization
Intermediate 8 steps
php 
<?php
 
namespace App\Support;
 

Recursively finding files with SPL iterators in PHP

recursion iterators filesystem
Intermediate 7 steps
python 
from contextlib import contextmanager
from typing import Iterator
 
import psycopg2

Streaming Postgres rows with a server-side cursor

generators context-managers database-streaming
Intermediate 7 steps
rust 
use std::time::Duration;
 
use axum::{
    http::{header, HeaderValue, Request},

Serving fingerprinted assets in Axum

static-assets http-caching middleware
Intermediate 7 steps
typescript 
type MatchSegment = {
  text: string;
  matched: boolean;
};

Splitting text into highlighted match segments

regex string-matching text-highlighting
Intermediate 8 steps