Code Explainers

Code explainers tagged #dependency-injection

typescript 
import { Component, OnInit, inject } from '@angular/core';
import { ActivatedRoute, Router } from '@angular/router';
import { FormBuilder } from '@angular/forms';
import { debounceTime, map } from 'rxjs/operators';

Syncing an Angular filter form with the URL

reactive-forms query-params rxjs
Intermediate 8 steps
typescript 
import { inject } from '@angular/core';
import {
  ActivatedRouteSnapshot,
  CanActivateFn,

How a functional route guard works in Angular

route-guards dependency-injection rxjs
Intermediate 5 steps
java 
package com.acme.billing.config;
 
import org.flywaydb.core.Flyway;
import org.flywaydb.core.api.MigrationVersion;

Customizing Flyway migrations in Spring

database-migrations flyway dependency-injection
Intermediate 6 steps
python 
from datetime import date
from enum import Enum
from typing import Annotated
 

Reusable query params with Pydantic in FastAPI

query-parameters validation pagination
Intermediate 8 steps
ruby 
require "digest"
 
class UploadDeduplicator
  CHUNK_SIZE = 64 * 1024

Deduplicating uploads by content hash

hashing deduplication streaming-io
Intermediate 7 steps
typescript 
import { Controller, Get, Param, StreamableFile, Res, NotFoundException, Header } from '@nestjs/common';
import { Response } from 'express';
import { createReadStream, promises as fsp } from 'fs';
import { join } from 'path';

Streaming CSV file downloads in NestJS

file-streaming http-headers error-handling
Intermediate 7 steps
java 
@RestController
@RequestMapping("/api/orders")
public class OrderController {
 

Content-negotiated API versioning in Spring

api-versioning content-negotiation rest
Intermediate 7 steps
typescript 
import { Controller, Get } from '@nestjs/common';
import {
  HealthCheck,
  HealthCheckService,

Liveness vs readiness probes in NestJS

health-checks dependency-injection observability
Intermediate 6 steps
java 
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface CurrentUser {
}

Injecting the current user in Spring MVC

annotations dependency-injection security
Intermediate 8 steps
typescript 
import {
  Controller,
  Post,
  Headers,

Verifying Stripe webhooks in NestJS

webhooks signature-verification event-handling
Intermediate 7 steps
python 
import os
from datetime import datetime, timezone
 
import jwt

JWT bearer auth as a FastAPI dependency

authentication jwt dependency-injection
Intermediate 7 steps
go 
package middleware
 
import (
	"crypto/subtle"

Building an API-key middleware in Gin

middleware authentication dependency-injection
Intermediate 5 steps
java 
@Component
@Order(20)
public class ProductSearchIndexRunner implements ApplicationRunner {
 

Rebuilding a search index at Spring startup

startup-hook batching streaming
Intermediate 8 steps
typescript 
import { Injectable, signal, computed } from '@angular/core';
import {
  HttpInterceptorFn,
  HttpContextToken,

Tracking HTTP loading state in Angular

signals http-interceptor reference-counting
Intermediate 8 steps
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
java 
@Service
public class OrderCheckoutService {
 
    private final OrderRepository orderRepository;

How @Transactional guards a Spring checkout

dependency-injection transactions atomicity
Intermediate 6 steps
java 
@Service
public class OrderMetricsService {
 
    private final MeterRegistry registry;

Instrumenting orders with Micrometer in Spring

metrics micrometer observability
Intermediate 8 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