Using sqlite3_update_hook

[ceymard]

It would be nice to be able to subscribe to events using the sqlite3_update_hook function.

How about adding a setUpdateHook() method to the Database instance ?

I know that this function only fires for updates within the same database connection, but it would still be of use to me (probably).

[JoshuaWise]

You can do the same thing (and with more control) by combining triggers and custom functions:

db.prepare('CREATE TABLE data (a, b, c)').run();
db.prepare('INSERT INTO data VALUES (12, 34, 56)').run();

// This is your actual update hook
db.register({ varargs: true }, function logger(...values) {
  console.log(`row updated to (${values.join(', ')})`);
});

db.prepare('CREATE TRIGGER updateHook AFTER UPDATE ON data BEGIN SELECT logger(NEW.a, NEW.b, NEW.c); END').run();

db.prepare('UPDATE data SET a = 78').run();
// => row updated to (78, 34, 56)

[ceymard]

Didn't think about it. There is no need for this, then.

[JoshuaWise]

😃

[wmertens]

Nice! Will this trigger also fire if another connection updates the table? I think this use case warrants mentioning in the readme, btw…

[JoshuaWise]

@wmertens this will only work if the logger() function is registered with the connection that tries to update the table. Otherwise an error will be thrown by SQLite

[wmertens]

Aww. I'll just continue polling the DB then 😢. I could probably improve that by using filesystem monitoring and watching the DB file for changes…

[JoshuaWise]

Yeah unfortunately that's the only way to read changes made by other connections. Even sqlite3_update_hook() only receives changes made by the same connection.

[crossle]

@JoshuaWise No register function?

[crossle]

The mean function function

[tantaman]

@wmertens this will only work if the logger() function is registered with the connection that tries to update the table. Otherwise an error will be thrown by SQLite

Using a temp trigger allows you to create a trigger that invokes functions only installed on the current connection. You still, however, have the problem of not seeing changes made by other connections with this method.