Back in Stock Notification for E-Commerce

Development of Back In Stock Notification for E-Commerce

When a product goes out of stock — the customer leaves. The "Notify When In Stock" form retains this demand: instead of losing a customer, the store gets a contact of an interested buyer and an opportunity to return them when the product appears. Development of this functionality takes 1–2 business days.

Data Schema

CREATE TABLE back_in_stock_requests (
    id BIGSERIAL PRIMARY KEY,
    product_id BIGINT NOT NULL REFERENCES products(id) ON DELETE CASCADE,
    variant_id BIGINT REFERENCES product_variants(id) ON DELETE CASCADE,
    user_id BIGINT REFERENCES users(id) ON DELETE SET NULL,
    email VARCHAR(255) NOT NULL,
    notified_at TIMESTAMP,
    created_at TIMESTAMP DEFAULT NOW()
);

CREATE UNIQUE INDEX idx_bis_email_product
    ON back_in_stock_requests(email, product_id, COALESCE(variant_id, 0))
    WHERE notified_at IS NULL;

Unique index prevents duplicate subscriptions from one email to one product/variant.

Subscription Form

Form is shown instead of "Add to Cart" button when stock = 0:

const BackInStockForm = ({ product, variant }: BackInStockProps) => {
  const { user } = useAuth();
  const [submitted, setSubmitted] = useState(false);
  const { register, handleSubmit, formState: { errors, isSubmitting } } = useForm({
    defaultValues: { email: user?.email ?? '' },
  });

  const onSubmit = async (data: { email: string }) => {
    await api.post('/back-in-stock', {
      product_id: product.id,
      variant_id: variant?.id ?? null,
      email: data.email,
    });
    setSubmitted(true);
  };

  if (submitted) {
    return (
      <div className="flex items-center gap-2 text-green-600 text-sm">
        <CheckIcon className="w-4 h-4" />
        <span>We'll notify you when this product is back in stock</span>
      </div>
    );
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-2">
      <p className="text-sm text-gray-600">Out of stock. Leave your email — we'll notify you when it arrives.</p>
      <div className="flex gap-2">
        <input
          type="email"
          placeholder="[email protected]"
          className="flex-1 border rounded px-3 py-2 text-sm"
          {...register('email', { required: true, pattern: /^[^\s@]+@[^\s@]+\.[^\s@]+$/ })}
        />
        <Button type="submit" size="sm" loading={isSubmitting}>
          Notify
        </Button>
      </div>
      {errors.email && <p className="text-red-500 text-xs">Enter a valid email</p>}
    </form>
  );
};

Subscription API Endpoint

public function subscribe(Request $request): JsonResponse
{
    $request->validate([
        'product_id' => 'required|exists:products,id',
        'variant_id' => 'nullable|exists:product_variants,id',
        'email'      => 'required|email|max:255',
    ]);

    // Check that product is indeed out of stock
    $product = Product::find($request->product_id);
    if ($product->stock > 0) {
        return response()->json(['message' => 'Product is already in stock'], 422);
    }

    BackInStockRequest::firstOrCreate([
        'product_id' => $request->product_id,
        'variant_id' => $request->variant_id,
        'email'      => strtolower($request->email),
        'notified_at' => null,
    ], [
        'user_id' => $request->user()?->id,
    ]);

    return response()->json(['message' => 'Subscription confirmed']);
}

Automatic Sending on Stock Replenishment

Trigger fires when product stock is updated. This can happen through:

• Import from 1C/ERP
• Manual update in admin panel
• API from supplier

// Observer on Product or ProductVariant model
class ProductObserver
{
    public function updated(Product $product): void
    {
        if ($product->isDirty('stock') && $product->stock > 0 && $product->getOriginal('stock') === 0) {
            NotifyBackInStockSubscribers::dispatch($product)->onQueue('notifications');
        }
    }
}

Notification sending job:

class NotifyBackInStockSubscribers implements ShouldQueue
{
    public function handle(): void
    {
        $requests = BackInStockRequest::where('product_id', $this->product->id)
            ->whereNull('variant_id')
            ->whereNull('notified_at')
            ->get();

        foreach ($requests as $request) {
            Mail::to($request->email)->queue(new BackInStockNotification($this->product, $request));
            $request->update(['notified_at' => now()]);
        }
    }
}

Email Notification

Email contains:

• Product photo and name
• Current price (considering applicable discounts)
• Direct link to product with UTM tag utm_source=back_in_stock
• Warning "Limited quantity — hurry to buy"

Email is sent once when product arrives. No repeat notifications — notified_at records the sending fact.

Unsubscribe

"Unsubscribe" link in email leads to /back-in-stock/unsubscribe?token={token}. Token is HMAC signature of email + product_id:

$token = hash_hmac('sha256', "{$request->email}:{$request->product_id}", config('app.key'));

Analytics

Block metrics:

• Number of active subscriptions by product
• Subscriber to purchase conversion (via UTM + orders)
• Time from subscription to product arrival
• Percentage of subscribers who managed to buy after notification

Products with large number of subscriptions — signal to reorder from supplier.