supabase/apps/docs/content/guides/realtime/migrate-from-postgres-changes.mdx

---
title: 'Migrate to Broadcast Changes'
subtitle: 'How to migrate from Postgres Changes to Broadcast Changes'
description: 'How to migrate from Postgres Changes to Broadcast Changes'
sidebar_label: 'Migrate to Broadcast Changes'
---

Postgres Changes has some [limitations](/docs/guides/realtime/postgres-changes#limitations) as your application scales. To continue broadcasting database changes to users as you scale, you can use Broadcast Changes.

## Example application using Postgres Changes

Here we have a simple chess application that has a game id and we want to track whenever we have new moves happening for a given game id.

We store this information in a `public.moves` table and every time a new move is added to a given `game_id` we want to receive the changes in our connected Realtime client

<Image
  alt="Schema used for our example"
  src={{
    light:
      '/docs/img/guides/realtime/realtime-broadcast-changes-migration-schema-example-light.png',
    dark: '/docs/img/guides/realtime/realtime-broadcast-changes-migration-schema-example-dark.png',
  }}
/>

In our client we will have our implementation to receive insert events with the usual code:

```javascript
const gameId = '4a8bbe89-f601-4414-bd47-8d0f7ab2a31a'
const changes = supabase
  .channel('chess-moves')
  .on(
    'postgres_changes',
    {
      event: 'INSERT',
      schema: 'public',
      table: 'moves',
      filter: `game_id=eq.${gameId}`,
    },
    (payload) => console.log(payload)
  )
  .subscribe()
  ...
```

## Migrate to broadcast changes

To use Broadcast Changes, first familiarize yourself with the [Broadcast Changes implementation](/docs/guides/realtime/broadcast#trigger-broadcast-messages-from-your-database).

### Set up authorization

Broadcast Changes is private by default, using [Realtime Authorization](/docs/guides/realtime/authorization) to control access. First, set up RLS policies to control user access to relevant messages:

```sql
CREATE POLICY "authenticated can listen to game moves"
ON "realtime"."messages"
FOR SELECT
TO authenticated
USING (
  EXISTS (
    SELECT 1
    FROM game_users
    WHERE (SELECT auth.uid()) = user_id
      AND (select realtime.topic()) = 'games:' || game_id::text
      AND realtime.messages.extension = 'broadcast'
  )
);
```

### Set up trigger function

We need to define our trigger function to adapt to our use case and use the provided function `realtime.broadcast_changes`

```sql
CREATE OR REPLACE FUNCTION public.broadcast_moves() RETURNS trigger AS $$
BEGIN
    PERFORM realtime.broadcast_changes(
	    'games:' || NEW.game_id::text,   -- topic
		   TG_OP,                          -- event
		   TG_OP,                          -- operation
		   TG_TABLE_NAME,                  -- table
		   TG_TABLE_SCHEMA,                -- schema
		   NEW,                            -- new record
		   OLD                             -- old record
		);
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;
```

### Setup trigger with created function

Now we need to setup our trigger to capture the events we want

```sql
CREATE TRIGGER chess_move_changes
AFTER INSERT ON public.moves
FOR EACH ROW
EXECUTE FUNCTION public.broadcast_moves();
```

### **Listen to changes in client**

Finally you can setup your client to listen for your events

```js
const gameId = '4a8bbe89-f601-4414-bd47-8d0f7ab2a31a'
await supabase.realtime.setAuth() // Needed for Realtime Authorization
const changes = supabase
  .channel(`games:${gameId}`)
  .on(
    'broadcast',
    {
      event: 'INSERT',
    },
    (payload) => console.log(payload)
  )
  .subscribe()
```