A Pragmatic guide to SOLID principles in Symfony

Applying SOLID’s five timeless principles to craft clean, testable, and future-proof Symfony code

Photo by Sarah Dorweiler on Unsplash

Why bother?

Symfony already gives us a robust service container, autowiring, and a healthy dose of convention. Yet controllers still bloat, services quietly turn into God objects, and a single change request can feel like surgery. The five SOLID principles are a handy litmus test to keep that from happening. Below you’ll find Symfony-centric examples that you can paste into a project today — no ivory-tower theory, just patterns that keep velocity high and headaches low.

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1. Single Responsibility Principle — “One reason to wake up”

The problem

A controller that validates input, calculates tax, writes to the database and fires an email will change every time any of those concerns change.

The Symfony-style fix

// src/Controller/CheckoutController.php
final class CheckoutController extends AbstractController
{
    public function __invoke(
        Request $request,
        OrderProcessor…