Supabase Auth Triggers: A Step-by-Step Guide

Hey everyone! So, you’re diving into Supabase and want to supercharge your user authentication by adding custom logic? Creating triggers on Supabase auth users is a game-changer, letting you automate tasks whenever a user signs up, signs in, or even updates their profile. It’s like having a personal assistant for your database! In this guide, we’ll walk through exactly how to set this up, making sure you guys understand every step without any confusion. We’ll cover the why and the how , so you can confidently implement these powerful features in your projects.

Why Use Supabase Auth Triggers?

Alright, let’s talk about why you’d even want to mess with Supabase auth triggers . Think about it – every time a new user signs up, what do you want to happen? Maybe you need to send them a welcome email, create a default user profile in another table, or even log their registration for analytics. Or perhaps when a user updates their email, you need to invalidate old sessions or send a verification link. Manually doing these things after a user action is tedious and error-prone. That’s where triggers come in. They’re database functions that automatically execute in response to specific events on your tables. In Supabase, we’re focusing on the auth.users table (and related tables like auth.identities ). When someone signs up via Supabase Auth, it fires off events. By setting up triggers, you can hook into these events and run your custom SQL code. This means automation, consistency, and cleaner code for your backend logic. Instead of writing complex application-level code to handle these scenarios, you can let the database do the heavy lifting, ensuring that your critical post-authentication actions always happen, every single time. It simplifies your application’s codebase significantly, allowing you to focus on building user-facing features rather than backend plumbing. Plus, it’s incredibly efficient because these operations are happening directly within the database, minimizing network latency and potential race conditions.

Understanding Supabase Auth Events

Before we jump into writing code, it’s crucial to understand the events that Supabase auth triggers can react to. Supabase, built on PostgreSQL, leverages PostgreSQL’s robust trigger system. When it comes to authentication, the primary events you’ll be interested in typically revolve around user creation and modification. The auth.users table is central to this. Common events include:

• INSERT : This event fires whenever a new user record is created in the auth.users table. This is your go-to for actions that need to happen immediately after a user signs up. Think creating a corresponding entry in your profiles table, sending a welcome email, or adding them to a default group.
• UPDATE : This event fires when an existing user record is modified. While you can trigger on any column update, you’ll often want to specifically look for changes in critical fields like email , email_confirmed_at , or perhaps custom metadata fields you’ve added.
• DELETE : This event fires when a user record is removed. This is less common for direct auth triggers because Supabase Auth has its own mechanisms for user deletion, but in specific scenarios, you might want to clean up related data across your application when a user is permanently removed.

It’s important to note that Supabase Auth itself manages the lifecycle of the auth.users table . While you can create triggers on auth.users , you need to be extremely careful. Supabase often performs its own internal operations on this table, and interfering incorrectly can break authentication. A safer and more common pattern is to trigger off events in your own tables that are related to user actions, or to use PostgreSQL’s Row Level Security (RLS) policies which can execute functions. However, for specific use cases like adding initial data to a profiles table right after a user is created, triggering on auth.users can be very effective if done correctly.

Best Practice: Often, the most robust approach is to use Supabase’s Post Authentication hooks within your auth functions or to create triggers on your application tables that are populated after a user is created. For example, when a user record is inserted into your profiles table (which you’d typically populate via an auth.users INSERT trigger or an API call), you can then create triggers on that profiles table. However, for the sake of demonstrating direct triggers on auth users, we will proceed with that approach, keeping the caveats in mind. You’ll typically be writing trigger functions in PostgreSQL’s procedural language, PL/pgSQL, which is powerful and widely used.

Setting Up Your First Trigger: A Welcome Profile

Let’s get practical, guys! One of the most common use cases for creating triggers on Supabase auth users is to automatically create a corresponding profile for each new user in a separate profiles table. This keeps your user data organized and lets you add custom fields beyond what auth.users provides.

First, ensure you have a profiles table set up. It might look something like this:

CREATE TABLE public.profiles (
  id uuid PRIMARY KEY REFERENCES auth.users(id),
  created_at timestamp with time zone DEFAULT now(),
  username text UNIQUE,
  avatar_url text
);

-- Enable Row Level Security (RLS) for the profiles table
ALTER TABLE public.profiles ENABLE ROW LEVEL SECURITY;

-- Allow authenticated users to select their own profile
CREATE POLICY "Users can view their own profile." ON public.profiles
FOR SELECT USING (auth.uid() = id);

-- Allow users to update their own profile (adjust as needed)
CREATE POLICY "Users can update their own profile." ON public.profiles
FOR UPDATE USING (auth.uid() = id);

-- Allow users to insert their own profile (only if they have an auth.user)
-- NOTE: We will handle insertion via a trigger, so direct INSERT might be restricted

Now, we need a function that will be executed by the trigger. This function will insert a new row into the profiles table whenever a new user is added to auth.users . Here’s the PL/pgSQL function:

”`sql CREATE OR REPLACE FUNCTION public.handle_new_user() RETURNS TRIGGER AS $$ BEGIN – Check if the new user record is valid and has an ID IF NEW.id IS NULL THEN

RAISE EXCEPTION "New user record must have an ID";

END IF;

– Insert a new profile for the newly created user INSERT INTO public.profiles (id, username) VALUES (NEW.id, NEW.raw_user_meta_data ->> ‘username’); – Example: using metadata for initial username

– IMPORTANT: Return NEW to allow the original INSERT operation on auth.users to complete. RETURN NEW; END; $$ LANGUAGE plpgsql SECURITY DEFINER;