Thin

Thin is an informal qualifier applied to a class that has very few responsibilities: it receives input, calls one collaborator, and returns output. It contains no business logic of its own.

A thin controller delegates all domain work to services, repositories, or domain objects. This makes it trivially testable and easy to replace.

The term is often used in the phrase thin controllers, fat models, which is a common recommendation in MVC frameworks.

The opposite is a fat class. Taken to the extreme, a thin class becomes a mere passthrough: at that point it may be unnecessary altogether.

<?php

// Thin controller example
class ArticleController {
    public function __construct(private ArticleService $articles) {}

    public function show(int $id): Response {
        return response()->json(
            $this->articles->findOrFail($id)
        );
    }
}

?>

Documentation

See also Thin controllers, fat models.

Related : Fat, Slim, Thin Method, Fat Controller, Controller, Single Responsability Principle (SRP), Service