Functions

How to Create Functions in Supabase

Creating Functions Locally

To create a function locally using SQL in Supabase, you can write a SQL CREATE FUNCTION statement. Here is a simple example:

CREATE FUNCTION update_user_last_login(user_id uuid) 
RETURNS void
LANGUAGE plpgsql
AS $$
BEGIN
  UPDATE users SET last_login = NOW() WHERE id = user_id;
END;
$$;

This function updates the last_login field of the users table for a given user_id.

Creating Functions Remotely

You can also create functions remotely via Supabase’s dashboard or using the Supabase CLI.

1. Via Supabase Dashboard:

   • Navigate to your Supabase project.
   • Go to the SQL Editor section.
   • Write the function SQL query in the editor and execute it.

2. Using Supabase CLI: Run SQL queries via the CLI to create a function.

supabase db execute <<'EOF'
CREATE FUNCTION update_user_last_login(user_id uuid) 
RETURNS void
LANGUAGE plpgsql
AS $$
BEGIN
  UPDATE users SET last_login = NOW() WHERE id = user_id;
END;
$$;
EOF

Using Supabase Functions with RLS Policies and Triggers

Using Functions in Row Level Security (RLS) Policies

Row Level Security (RLS) policies allow fine-grained control over who can access specific rows in a table. You can integrate Supabase functions into RLS policies for advanced security configurations.

Example:

CREATE POLICY "Can access own data"
ON profiles
FOR SELECT
USING (auth.uid() = user_id AND check_user_permission(user_id));

In this example, the check_user_permission(user_id) function can contain additional logic to validate user-specific permissions before granting access.

Using Functions in Triggers

Triggers are automated database operations that execute before or after certain events, such as inserts, updates, or deletions. Supabase functions can be triggered by such events to perform specific actions.

Example:

CREATE TRIGGER update_last_login
AFTER UPDATE ON users
FOR EACH ROW
EXECUTE FUNCTION update_user_last_login(NEW.id);

This trigger automatically updates the last_login field whenever a user’s profile is updated.

Advantages of Using Supabase Functions in a Next.js Application

1. Performance Optimization: Functions help reduce the need for complex logic in the frontend, minimizing the number of API requests from your Next.js application. This reduces the overall memory and bandwidth consumption, especially for operations like filtering and aggregation, which are better handled at the database level.

2. Improved Security: Combining functions with RLS policies ensures that security logic is implemented directly within the database, safeguarding sensitive data even if the application layer is compromised.

3. Enhanced Maintainability: With Supabase functions, updates to business logic only need to occur at the database level, simplifying the management of database-related code in a Next.js application.

4. Data Integrity: Functions used with triggers ensure data integrity by automatically performing certain operations (e.g., logging, auditing) when records are modified. This reduces the chances of human error or missed updates in complex workflows.