React to database changes

Patterns 4 · 3:49

A change tracking integration publishes every insert, update and delete in a database table into a channel, and a watcher route reacts to each one. The database administrator first turns on the database's own change feature.

Download the mp4Recorded on 2026.2

What it covers

Scaffolding the change tracking with weikio init --kind change-tracking
The filled document for PostgreSQL and public.invoice, with its placeholders from variables and a secret
The channel invoice-changes, made with weikio channel create, where each change is one stored event
The watcher route, started by the kamelet weikio-event-source, with its log step
Three changes to invoice 1041, read back with weikio events show and weikio logs
The agent dev as the leading copy, and each change on the admin UI's Changes tab

Commands in this video

Terminal

$ weikio init invoice-tracking --kind change-tracking
$ weikio channel create sandbox/invoice-changes
$ weikio apply -f ./invoice-tracking
$ weikio deploy sandbox/invoice-tracking --env devtest
$ weikio run ./invoice-watcher --no-logs
$ psql -d erp -c "INSERT INTO invoice (id, customer, amount, status) VALUES (1041, 'Lakeside Bakery', 640, 'open')"
$ weikio events show sandbox/invoice-changes --seq 1
$ psql -d erp -c "UPDATE invoice SET status = 'paid' WHERE id = 1041"
$ psql -d erp -c "DELETE FROM invoice WHERE id = 1041"
$ weikio logs sandbox/invoice-watcher --since 10m

Transcript

0:01An invoice changes in the database.
0:03Other systems must hear of every change.
0:12The three changes to invoice 1041 left no rows.
0:16The database's administrator switches on its change feature.
0:23The tools are a change tracking, a channel, and the kamelet weikio-event-source.
0:33The change tracking is an integration of its own kind.
0:36The command wrote its scaffold, and the tracking publishes every insert,
0:41update and delete into a channel.
0:44The scaffold names SQL Server, and the filled document names postgres,
0:50public.invoice and another channel, invoice-changes.
0:56The placeholders read variables and a secret:
0:59erp-db-host, erp-db-user, erp-db-password.
1:07A channel is a hub service that keeps its events.
1:11Every change the tracking publishes is one stored event.
1:15It holds an op letter, c for create, u for update,
1:19d for delete, and the row before and after.
1:22The command created the channel sandbox/invoice-changes.
1:29The kamelet weikio-event-source starts the watcher's route on the channel.
1:34The route sees each stored event as it lands.
1:37Its file shows the kamelet, the channel and the log step.
1:41The log step prints each change's operation, invoice and status.
1:48The apply sends the folder to the hub.
1:52The change tracking is created with no warning, because the channel exists.
1:57The deploy answers with one agent running.
2:02The watcher runs, from the kamelet weikio-event-source.
2:11The database's own tool inserts invoice 1041.
2:19Two seconds later, the channel holds one stored event.
2:23It carries op c, before null and after the new row.
2:32The tool updates the row for invoice 1041.
2:35Then the row is removed.
2:42The channel holds three stored events.
2:49weikio logs reads ten minutes of the watcher's log.
2:53The received lines read op c, u, d.
3:03The change tracking runs one copy at a time, dev is the leader.
3:10Its Changes lists each change for invoice 1041.
3:16The event holds op u, open in before and paid in after.
3:25The change tracking publishes every insert,
3:28update and delete of the table into a channel.
3:31The channel invoice-changes keeps each one as a stored event.
3:35The kamelet weikio-event-source starts the watcher's route,
3:39and the route sees each event.

Next in this track

Patterns 5 · 2:58 One copy at a time