php 54 lines · 7 steps

Validating coupons with Laravel's Pipeline

A checkout service runs a coupon through a chain of validation handlers, then applies the discount inside a transaction.

Explained by highlit

Laravel Intermediate pipeline chain of responsibility transactions validation dependency injection

1<?php
2 
3namespace App\Services\Checkout;
4 
5use App\Models\Cart;
6use App\Models\Coupon;
7use App\Exceptions\CouponException;
8use Illuminate\Pipeline\Pipeline;
9use Illuminate\Support\Facades\DB;
10 
11class CouponResolver
12{
13    protected array $handlers = [
14        Handlers\EnsureCouponIsActive::class,
15        Handlers\EnsureWithinUsageLimit::class,
16        Handlers\EnsureMinimumSpend::class,
17        Handlers\EnsureCartEligibility::class,
18        Handlers\ApplyDiscountAmount::class,
19    ];
20 
21    public function __construct(protected Pipeline $pipeline)
22    {
23    }
24 
25    public function apply(Cart $cart, string $code): DiscountResult
26    {
27        $coupon = Coupon::where('code', strtoupper($code))->first();
28 
29        if (! $coupon) {
30            throw CouponException::notFound($code);
31        }
32 
33        return DB::transaction(function () use ($cart, $coupon) {
34            $context = new DiscountContext(
35                cart: $cart,
36                coupon: $coupon,
37                subtotal: $cart->subtotal(),
38            );
39 
40            $resolved = $this->pipeline
41                ->send($context)
42                ->through($this->handlers)
43                ->thenReturn();
44 
45            $coupon->increment('times_redeemed');
46 
47            return new DiscountResult(
48                coupon: $coupon,
49                discount: $resolved->discount,
50                total: max(0, $context->subtotal - $resolved->discount),
51            );
52        });
53    }
54}

01 / 01

STEP 01

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Three takeaways

1A pipeline turns a tangle of validation checks into an ordered, individually testable list of handlers.
2Wrapping the read, mutation, and result in a single transaction keeps redemption counts consistent under concurrent use.
3Passing a mutable context object through each stage lets handlers accumulate state like the computed discount.

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