Alright, let's dive into data retention with Supabase. It's important to know that data retention here is all about how you use Supabase Database and Supabase Storage. Supabase Database uses PostgreSQL, so its data retention rules follow PostgreSQL's system. Meanwhile, Supabase Storage follows PostgREST's policies.

One key thing to remember: Supabase won't automatically delete your data after a certain time. So, you'll need to write scripts to clean up old data regularly.

First things first, figure out what your data retention needs are. This means deciding how long you want to keep different types of data on Supabase. It could be user info, transaction records, logs, and so on.

Next up, you'll need to create a script to delete old data from your database based on your retention policies. You can write this script in SQL, using PostgreSQL’s DELETE command. Here's a simple example:

DELETE FROM table_name
WHERE condition;

In the condition part, you can set rules based on the age of the data. For instance, if you want to delete user records older than a year, your SQL command would look like this:

DELETE FROM users
WHERE created_at < NOW() - INTERVAL '1 year';

You'll probably want this script to run automatically at regular intervals. That's where PostgreSQL's job scheduling module, pg_cron, comes in handy. You can use it to schedule your data deletion script.

Here's a basic example of setting up a cron job in PostgreSQL:

SELECT cron.schedule('every day at 1 am', $$ DELETE FROM table_name WHERE condition; $$);

Using our previous example for deleting old user records:

SELECT cron.schedule('every day at 1 am', $$ DELETE FROM users WHERE created_at < NOW() - INTERVAL '1 year'; $$);

For Supabase Storage, you'll need a different approach. Supabase Storage doesn't support SQL queries directly, but you can use the Supabase Client Libraries to manage your storage.

You can write a script in JavaScript (Node.js) using the Supabase JavaScript Library to delete old files. Here's a basic example:

// Required Libraries
const { createClient } = require("@supabase/supabase-js");

// Supabase Client Initialization
const supabaseUrl = "YOUR_SUPABASE_URL";
const supabaseKey = "YOUR_SUPABASE_KEY";
const supabase = createClient(supabaseUrl, supabaseKey);

// Data Retention Function
async function deleteOldFiles() {
    const olderThanDate = new Date();
    olderThanDate.setFullYear(olderThanDate.getFullYear() - 1); // 1 year old
    
    const { data, error } = await supabase.storage.list("your-bucket-name");

    if (error) {
        console.error("Error fetching files:", error);
        return;
    }

    for (const file of data) {
        const { last_modified: lastModified } = file;
        if (new Date(lastModified) < olderThanDate) {
            const { error: deleteError } = await supabase.storage
                .from("your-bucket-name")
                .remove([file.name]);

            if (deleteError) {
                console.error("Error deleting file:", deleteError);
            }
        }
    }
}

// Invoke Function
deleteOldFiles();

This script lists all files in a specified bucket, then loops through each file to check if it’s older than a certain date. If it is, the file gets deleted. You can then run this script as a cron job on your server.

These steps should help you set up basic data retention policies on your Supabase platform. But remember, always test these scripts and policies thoroughly before deploying them.