Logical replication, need to get only the changed column values, not all column values, on update event row

[uasan]

Hello.

When an update event occurs, all columns are sent to the subscription handler, even those that were not updated. In my business logic, I need to understand which columns have changed their values. How can this be done?

Thanks.

[Eomm]

YOu need to enable full identity:

await sql`ALTER TABLE my_table REPLICA IDENTITY FULL`

Then the old argument of the subscribe's callback, will be set and a custom diff function must compare row with old:

  const { unsubscribe } = await subscriptionSql.subscribe(
    '*:my_table',
    (row, { command, relation, key, old }) => {
      // diff row vs old
    },
    () => {
      // Callback on initial connect and potential reconnects
    }
  )```