supabase-webhooks-events

Supabase Webhooks & Database Events

Overview

Supabase offers four complementary event mechanisms: Database Webhooks (trigger-based HTTP calls via pg_net), supabase_functions.http_request() (call Edge Functions from triggers), Postgres LISTEN/NOTIFY (lightweight pub/sub), and Realtime postgres_changes (client-side event subscriptions). This skill covers all four patterns with production-ready code including signature verification, idempotency, and retry handling.

Prerequisites

• Supabase project (local or hosted) with supabase CLI installed
• pg_net extension enabled: Dashboard > Database > Extensions > search "pg_net" > Enable
• @supabase/supabase-js v2+ installed for client-side patterns
• Edge Functions deployed for webhook receiver patterns

Step 1 — Database Webhooks with pg_net and Trigger Functions

Database webhooks fire HTTP requests when rows change. Under the hood, Supabase uses the pg_net extension to make async, non-blocking HTTP calls from within PostgreSQL.

Enable pg_net and Create the Trigger Function

-- Enable the pg_net extension (one-time)
CREATE EXTENSION IF NOT EXISTS pg_net WITH SCHEMA extensions;

-- Trigger function: POST to an Edge Function on every new order
CREATE OR REPLACE FUNCTION public.notify_order_created()
RETURNS trigger AS $$
BEGIN
  PERFORM net.http_post(
    url    := 'https://<project-ref>.supabase.co/functions/v1/on-order-created',
    headers := jsonb_build_object(
      'Content-Type', 'application/json',
      'Authorization', 'Bearer ' || current_setting('app.settings.service_role_key', true)
    ),
    body   := jsonb_build_object(
      'table',  TG_TABLE_NAME,
      'type',   TG_OP,
      'record', row_to_json(NEW)::jsonb,
      'old_record', CASE WHEN TG_OP = 'UPDATE' THEN row_to_json(OLD)::jsonb ELSE NULL END
    )
  );
  RETURN NEW;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

Attach Triggers for INSERT, UPDATE, DELETE

-- Fire on new rows
CREATE TRIGGER on_order_created
  AFTER INSERT ON public.orders
  FOR EACH ROW EXECUTE FUNCTION public.notify_order_created();

-- Fire on status changes only (conditional trigger)
CREATE OR REPLACE FUNCTION public.notify_order_status_changed()
RETURNS trigger AS $$
BEGIN
  IF OLD.status IS DISTINCT FROM NEW.status THEN
    PERFORM net.http_post(
      url    := 'https://<project-ref>.supabase.co/functions/v1/on-status-change',
      headers := '{"Content-Type": "application/json"}'::jsonb,
      body   := jsonb_build_object(
        'order_id',   NEW.id,
        'old_status', OLD.status,
        'new_status', NEW.status,
        'changed_at', now()
      )
    );
  END IF;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

CREATE TRIGGER on_order_status_changed
  AFTER UPDATE ON public.orders
  FOR EACH ROW EXECUTE FUNCTION public.notify_order_status_changed();

Using supabase_functions.http_request() (Built-in Helper)

Supabase provides a built-in wrapper that simplifies calling Edge Functions from triggers without managing headers manually:

-- This is the function Supabase auto-creates for Dashboard-configured webhooks
-- You can also call it directly in your own trigger functions
CREATE TRIGGER on_profile_updated
  AFTER UPDATE ON public.profiles
  FOR EACH ROW
  EXECUTE FUNCTION supabase_functions.http_request(
    'https://<project-ref>.supabase.co/functions/v1/on-profile-update',
    'POST',
    '{"Content-Type": "application/json"}',
    '{}',  -- params
    '5000' -- timeout ms
  );

Inspect pg_net Responses

-- Check recent HTTP responses (retained for 6 hours)
SELECT id, status_code, content, created
FROM net._http_response
ORDER BY created DESC
LIMIT 10;

-- Find failed requests
SELECT id, status_code, content
FROM net._http_response
WHERE status_code >= 400
ORDER BY created DESC;

Step 2 — Edge Function Webhook Receivers with Signature Verification

Webhook Receiver with Signature Verification

// supabase/functions/on-order-created/index.ts
import { createClient } from "https://esm.sh/@supabase/supabase-js@2";
import { serve } from "https://deno.land/[email protected]/http/server.ts";

interface WebhookPayload {
  type: "INSERT" | "UPDATE" | "DELETE";
  table: string;
  record: Record<string, unknown>;
  old_record: Record<string, unknown> | null;
}

// Verify webhook signature to prevent spoofing
async function verifySignature(
  body: string,
  signature: string,
  secret: string
): Promise<boolean> {
  const encoder = new TextEncoder();
  const key = await crypto.subtle.importKey(
    "raw",
    encoder.encode(secret),
    { name: "HMAC", hash: "SHA-256" },
    false,
    ["sign"]
  );
  const signed = await crypto.subtle.sign("HMAC", key, encoder.encode(body));
  const expected = Array.from(new Uint8Array(signed))
    .map((b) => b.toString(16).padStart(2, "0"))
    .join("");
  // Constant-time comparison
  if (signature.length !== expected.length) return false;
  let mismatch = 0;
  for (let i = 0; i < signature.length; i++) {
    mismatch |= signature.charCodeAt(i) ^ expected.charCodeAt(i);
  }
  return mismatch === 0;
}

serve(async (req) => {
  // Verify signature if webhook secret is configured
  const webhookSecret = Deno.env.get("WEBHOOK_SECRET");
  const rawBody = await req.text();

  if (webhookSecret) {
    const signature = req.headers.get("x-webhook-signature") ?? "";
    const valid = await verifySignature(rawBody, signature, webhookSecret);
    if (!valid) {
      return new Response(JSON.stringify({ error: "Invalid signature" }), {
        status: 401,
      });
    }
  }

  const payload: WebhookPayload = JSON.parse(rawBody);

  const supabase = createClient(
    Deno.env.get("SUPABASE_URL")!,
    Deno.env.get("SUPABASE_SERVICE_ROLE_KEY")!,
    { auth: { autoRefreshToken: false, persistSession: false } }
  );

  // Route by event type
  switch (payload.type) {
    case "INSERT": {
      console.log(`New ${payload.table} row:`, payload.record.id);

      // Example: log event, send notification, update related table
      await supabase.from("audit_log").insert({
        table_name: payload.table,
        action: "INSERT",
        record_id: payload.record.id,
        payload: payload.record,
      });
      break;
    }
    case "UPDATE": {
      console.log(`Updated ${payload.table}:`, payload.record.id);
      // Compare old and new to detect specific field changes
      if (payload.old_record?.status !== payload.record.status) {
        await supabase.from("notifications").insert({
          user_id: payload.record.user_id,
          message: `Status changed to ${payload.record.status}`,
        });
      }
      break;
    }
    case "DELETE": {
      console.log(`Deleted from ${payload.table}:`, payload.old_record?.id);
      break;
    }
  }

  return new Response(JSON.stringify({ received: true }), {
    headers: { "Content-Type": "application/json" },
  });
});

Idempotent Event Processing

Webhooks may be delivered more than once. Use an idempotency table to prevent duplicate processing:

// supabase/functions/idempotent-handler/index.ts
import { createClient } from "https://esm.sh/@supabase/supabase-js@2";

serve(async (req) => {
  const payload = await req.json();
  const eventId = `${payload.table}:${payload.type}:${payload.record.id}`;

  const supabase = createClient(
    Deno.env.get("SUPABASE_URL")!,
    Deno.env.get("SUPABASE_SERVICE_ROLE_KEY")!
  );

  // Check if already processed (upsert pattern)
  const { data: existing } = await supabase
    .from("processed_events")
    .select("id")
    .eq("event_id", eventId)
    .maybeSingle();

  if (existing) {
    return new Response(
      JSON.stringify({ skipped: true, reason: "already processed" }),
      { status: 200, headers: { "Content-Type": "application/json" } }
    );
  }

  // --- Your business logic here ---
  console.log(`Processing event: ${eventId}`);

  // Mark as processed (with TTL for cleanup)
  await supabase.from("processed_events").insert({
    event_id: eventId,
    processed_at: new Date().toISOString(),
  });

  return new Response(JSON.stringify({ processed: true }), {
    status: 200,
    headers: { "Content-Type": "application/json" },
  });
});

-- Idempotency table
CREATE TABLE public.processed_events (
  id         bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  event_id   text UNIQUE NOT NULL,
  processed_at timestamptz DEFAULT now()
);

-- Auto-cleanup old records (run via pg_cron or scheduled function)
DELETE FROM public.processed_events
WHERE processed_at < now() - interval '7 days';

Step 3 — Postgres LISTEN/NOTIFY and Realtime as Event Source

Postgres LISTEN/NOTIFY for Lightweight Pub/Sub

LISTEN/NOTIFY is PostgreSQL's built-in pub/sub. It does not persist messages and is best for ephemeral notifications between database functions or connected clients:

-- Trigger function that emits a NOTIFY on row change
CREATE OR REPLACE FUNCTION public.notify_changes()
RETURNS trigger AS $$
BEGIN
  PERFORM pg_notify(
    'db_changes',
    json_build_object(
      'table', TG_TABLE_NAME,
      'op',    TG_OP,
      'id',    COALESCE(NEW.id, OLD.id)
    )::text
  );
  RETURN COALESCE(NEW, OLD);
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER orders_notify
  AFTER INSERT OR UPDATE OR DELETE ON public.orders
  FOR EACH ROW EXECUTE FUNCTION public.notify_changes();

// Listen from a Node.js backend using pg driver
import { Client } from "pg";

const client = new Client({ connectionString: process.env.DATABASE_URL });
await client.connect();

await client.query("LISTEN db_changes");

client.on("notification", (msg) => {
  const payload = JSON.parse(msg.payload!);
  console.log(`${payload.op} on ${payload.table}: id=${payload.id}`);
});

Realtime postgres_changes as Client-Side Event Source

Supabase Realtime lets frontend clients subscribe to database changes without polling. Enable Realtime on your table first (Dashboard > Database > Replication).

import { createClient } from "@supabase/supabase-js";

const supabase = createClient(
  process.env.SUPABASE_URL!,
  process.env.SUPABASE_ANON_KEY!
);

// Subscribe to all changes on the orders table
const channel = supabase
  .channel("orders-events")
  .on(
    "postgres_changes",
    {
      event: "*",           // or 'INSERT' | 'UPDATE' | 'DELETE'
      schema: "public",
      table: "orders",
      filter: "status=eq.pending",  // optional: RLS-style filter
    },
    (payload) => {
      console.log("Change type:", payload.eventType);
      console.log("New row:", payload.new);
      console.log("Old row:", payload.old);

      // React to the change
      switch (payload.eventType) {
        case "INSERT":
          showToast(`New order #${payload.new.id}`);
          break;
        case "UPDATE":
          updateOrderInUI(payload.new);
          break;
        case "DELETE":
          removeOrderFromUI(payload.old.id);
          break;
      }
    }
  )
  .subscribe((status) => {
    console.log("Subscription status:", status);
  });

// Cleanup when done
// await supabase.removeChannel(channel);

Event-Driven Architecture: Combining Patterns

Use database triggers for server-side workflows and Realtime for client-side UI updates:

┌──────────────┐     INSERT      ┌──────────────────┐
│   Client     │ ──────────────► │  orders table     │
│  (browser)   │                 └────────┬─────────┘
│              │                          │
│  Realtime ◄──┼──── postgres_changes ────┤
│  (UI update) │                          │
└──────────────┘                          │ AFTER INSERT trigger
                                          ▼
                                 ┌──────────────────┐
                                 │  pg_net HTTP POST │
                                 │  → Edge Function  │
                                 └────────┬─────────┘
                                          │
                                          ▼
                                 ┌──────────────────┐
                                 │  Send email       │
                                 │  Update inventory │
                                 │  Log to audit     │
                                 └──────────────────┘

Output

After implementing these patterns you will have:

• Database trigger functions calling Edge Functions via pg_net on row changes
• Conditional triggers that fire only when specific columns change
• Edge Function webhook receivers with HMAC signature verification
• Idempotent event processing preventing duplicate side effects
• LISTEN/NOTIFY channels for lightweight inter-service communication
• Realtime subscriptions for live client-side UI updates
• An event-driven architecture combining server and client patterns

Error Handling

Error	Cause	Fix
pg_net returns 404	Edge Function not deployed or wrong URL	Run supabase functions deploy <name> and verify the URL matches
Webhook not firing	Trigger not attached or table not in publication	Check SELECT * FROM pg_trigger WHERE tgrelid = 'orders'::regclass;
Duplicate events processed	No idempotency layer	Add processed_events table with unique event_id constraint
Realtime not receiving	Table not added to Realtime publication	Dashboard > Database > Replication > enable the table
net._http_response shows 401	Invalid or missing auth header	Verify service_role_key is set in app.settings or vault
NOTIFY payload truncated	Payload exceeds 8000 bytes	Send only IDs in NOTIFY, fetch full record in the listener
Auth hook errors	Function raises exception	Check Dashboard > Logs > Auth; ensure function returns valid JSONB
Trigger silently fails	SECURITY DEFINER without search_path	Add SET search_path = public, extensions; to function

Examples

See examples.md for local webhook testing with ngrok and curl.

See signature-verification.md for Node.js HMAC signature verification.

See event-handler-pattern.md for a typed event dispatcher pattern.

Resources

• Database Webhooks — configure via Dashboard or SQL
• pg_net Extension — async HTTP from PostgreSQL
• Edge Functions — Deno-based serverless handlers
• Realtime postgres_changes — client-side subscriptions
• Auth Hooks — custom JWT claims and login events
• supabase-js Reference — channel().on() API

Next Steps

For performance optimization of triggers and queries, see supabase-performance-tuning. For production hardening including RLS policies on webhook-accessed tables, see supabase-security-basics.