Custom stock notification for 1C-Bitrix: a practical guide
Picture this: a popular item is out of stock, and a potential buyer leaves without leaving their contact details. You lose sales, and customers get frustrated. 1C-Bitrix has no built-in "notify when available" feature — the standard subscription component isn't provided. We solve this with custom development, using a separate subscription table or the subscribe module. Savings from not buying a ready-made module can be significant, and the payback period is short.
Why the standard subscription module falls short
The subscribe module is designed for newsletters, and adapting it for product subscriptions is a compromise. Each product (or SKU) is registered as a "rubric", and a subscription is treated as a subscription to that rubric. When stock appears, you send an email manually or via an agent. Drawbacks: no direct link to a specific product, difficult management, risk of duplicate emails. For small stores with a dozen items, this might work, but for catalogs with thousands of positions, a custom subscription table is better. In one project, we saw the subscribe module send three identical emails to the same subscriber — because of missing uniqueness. After migrating to a custom table, the issue disappeared.
How to set up stock notifications
Option 1: Via the subscription module
The subscribe module can be adapted, but it requires extra logic. For example, when stock changes, an agent checks subscriptions for that product and sends emails. However, this approach lacks flexibility: you can't store send date, status, or guarantee uniqueness. The time spent on adaptation is roughly the same as for a custom table, but the result is inferior.
Option 2: Custom subscription table
This is the better solution — create a separate table product_availability_notify with fields PRODUCT_ID, EMAIL, USER_ID, DATE_ADD, DATE_SENT, IS_SENT. Uniqueness on product-email pairs prevents duplicates. The subscription form is a simple HTML+AJAX form that appears when QUANTITY = 0. When stock appears, the OnProductUpdate event handler triggers. See the official OnProductUpdate documentation.
| Feature | Subscribe module | Custom table |
|---|---|---|
| Implementation complexity | Low | Medium |
| Storage flexibility | Low | High |
| Subscription uniqueness | Not guaranteed | Guaranteed |
| Extensibility | Limited | Full |
Trigger for sending notifications
The OnProductUpdate event from the catalog module fires when the QUANTITY field changes. In the handler, we check if QUANTITY became greater than zero while it was zero before — then we select all subscribers and send emails via a mail event. Example code:
AddEventHandler('catalog', 'OnProductUpdate', function($productId, $fields) { if (isset($fields['QUANTITY']) && (float)$fields['QUANTITY'] > 0) { $subscribers = NotifyTable::getList([ 'filter' => ['=PRODUCT_ID' => $productId, '=IS_SENT' => false], ])->fetchAll(); foreach ($subscribers as $subscriber) { \Bitrix\Main\Mail\Event::send([ 'EVENT_NAME' => 'PRODUCT_AVAILABLE_NOTIFY', 'LID' => SITE_ID, 'C_FIELDS' => [ 'EMAIL' => $subscriber['EMAIL'], 'PRODUCT_NAME' => $fields['NAME'], 'PRODUCT_URL' => $fields['DETAIL_PAGE_URL'], ], ]); } NotifyTable::updateMulti(['IS_SENT' => true], ['PRODUCT_ID' => $productId]); } }); Email template
Create a mail event type under Settings → Mail Events → Event Types. The event type PRODUCT_AVAILABLE_NOTIFY with fields EMAIL, PRODUCT_NAME, PRODUCT_URL. Configuration takes 1-2 hours.
Agent for periodic checks
If the OnProductUpdate event doesn't fire (e.g., stock is changed outside standard methods), set up a Bitrix agent that runs once an hour. It checks stock for products with active subscribers and sends emails. The agent is a reliable fallback.
Common mistakes during setup
Mistake #1: forgetting to clear the IS_SENT flag when stock reappears after being zero again. If a product goes out of stock and then becomes available again, the subscriber should receive a second notification. In our custom table, this is handled by resetting the flag when stock hits zero. Mistake #2: confusion with the SKU binding — we subscribe to a specific SKU, not the parent product. Mistake #3: incorrect mapping of mail fields — the email arrives with empty data. We catch all these during testing.
Setup steps and time estimates
| Step | Description | Time (hours) |
|---|---|---|
| 1. Create table | Migration for subscription table | 1-2 |
| 2. Subscription form | HTML + AJAX on product page | 2-3 |
| 3. Event handler | OnProductUpdate with stock check | 2-3 |
| 4. Mail event | Create event type and template | 1-2 |
| 5. Testing | Verify with 3-5 products | 1-2 |
| 6. Documentation | User guide | 1 |
What's included
- Subscription form (HTML + AJAX) on product page
- Custom subscription table with migration
- Event handler
OnProductUpdate(or agent) - Mail event and email template
- User documentation
- Admin training (30 minutes)
- 6-month warranty for correct operation
Timelines and cost
Basic setup (form + handler + email) takes 4–8 hours. If a subscription management page in the user account is needed, add 2-3 hours. The cost is calculated individually based on complexity, but the savings from avoiding a purchased module can be substantial. You get a stable, extensible solution.
Our experience: over 5 years of Bitrix development, 50+ e-store customisation projects. We can set up stock notifications turnkey with a guarantee of stable operation. Contact us to evaluate your project — get a free consultation.
How the agent works
The agent runs once an hour. It queries products that have subscribers with IS_SENT = false and checks their stock via CIBlockElement::GetList. If stock > 0, it sends emails using the same logic as the handler.