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Dependency Injection

Prerequisites

Before continuing, review the PSR-11 Container documentation and the byjg/config Dependency Injection documentation.

Overview​

Dependency Injection (DI) decouples your code from specific implementations, making it easier to swap dependencies based on environment or requirements.

Example: Environment-Specific Cache​

You might want caching enabled in production but disabled in development for easier debugging.

Development - config/dev/01-infrastructure.php:

<?php

use ByJG\Cache\Psr16\BaseCacheEngine;
use ByJG\Cache\Psr16\NoCacheEngine;
use ByJG\Config\DependencyInjection as DI;

return [
    BaseCacheEngine::class => DI::bind(NoCacheEngine::class)
        ->toSingleton(),
];

Production - config/prod/01-infrastructure.php:

<?php

use ByJG\Cache\Psr16\BaseCacheEngine;
use ByJG\Cache\Psr16\FileSystemCacheEngine;
use ByJG\Config\DependencyInjection as DI;

return [
    BaseCacheEngine::class => DI::bind(FileSystemCacheEngine::class)
        ->toSingleton(),
];

Usage in Code:

<?php

use ByJG\Config\Config;
use ByJG\Cache\Psr16\BaseCacheEngine;

// Get the cache instance (implementation depends on APP_ENV)
$cache = Config::get(BaseCacheEngine::class);

// Use it the same way regardless of environment
$cache->set('key', 'value', 3600);
$value = $cache->get('key');

The application automatically returns the correct implementation based on the APP_ENV environment variable.

Common DI Patterns​

Constructor Injection​

DummyService::class => DI::bind(DummyService::class)
    ->withInjectedConstructor()
    ->toSingleton(),

The container automatically injects dependencies defined in the constructor based on their type hints.

Constructor with Parameters​

JwtWrapper::class => DI::bind(JwtWrapper::class)
    ->withConstructorArgs([
        Param::get('API_SERVER'),
        Param::get(JwtKeyInterface::class)
    ])
    ->toSingleton(),

Mix environment parameters and other dependencies.

Factory Method​

DbDriverInterface::class => DI::bind(Factory::class)
    ->withFactoryMethod("getDbRelationalInstance", [
        Param::get('DBDRIVER_CONNECTION')
    ])
    ->toSingleton(),

Use a factory method instead of a constructor.

Singleton vs Transient​

// Singleton - Same instance every time
MyService::class => DI::bind(MyService::class)->toSingleton(),

// Transient - New instance every time
MyService::class => DI::bind(MyService::class),

Configuration Organization​

Dependencies are organized by layer in numbered files:

  • 01-infrastructure.php - Database, Cache, Logging
  • 02-security.php - JWT, Authentication, User Management
  • 03-api.php - OpenAPI, Routes, Middleware
  • 04-repositories.php - Data access layer
  • 05-services.php - Business logic layer
  • 06-external.php - Email, SMS, external APIs

This organization makes it easy to find and modify related configurations.