In general, when you implement an event listener, you're supposed to be careful
to avoid triggering the event again.
So, yes, your use-case is tricky to implement, but it's sufficiently rare that
it's not worth complicating the Trigger
API for it.
Christian Bauer wrote:
> On Nov 29, 2011, at 18:28 , Noel Grandin wrote:
>
>> Implement the Trigger interface and check the oldRow vs newRow
>> parameters to see which fields have changed.
> This is the workaround:
>
> public class UpdateLastModifiedTrigger extends TriggerAdapter {
>
> public static final String COLUMN_ID = "ID";
> public static final String COLUMN_LASTMODIFIED = "LASTMODIFIED";
>
> protected String tableName;
>
> @Override
> public void init(Connection conn, String schemaName, String triggerName,
> String tableName, boolean before, int type) throws SQLException {
> super.init(conn, schemaName, triggerName, tableName, before, type);
> this.tableName = tableName;
> }
>
> @Override
> public void fire(Connection conn, ResultSet oldRow, ResultSet newRow)
> throws SQLException {
> if (newRow == null ) return; // This is a DELETE
>
> if (oldRow != null) {
> // This is an UPDATE
> // Yes, our UPDATE statement below will fire this trigger again,
> filter that!
> Timestamp oldTimestamp = oldRow.getTimestamp(COLUMN_LASTMODIFIED);
> Timestamp newTimestamp = newRow.getTimestamp(COLUMN_LASTMODIFIED);
> if (oldTimestamp == null)
> return;
> if (oldTimestamp.getTime() != newTimestamp.getTime())
> return;
> }
>
> PreparedStatement statement = conn.prepareStatement(
> "update " + tableName +
> " set " + COLUMN_LASTMODIFIED + " =
> current_timestamp()" +
> " where " + COLUMN_ID + " = ?"
> );
> // This assumes the PK column is named "ID"
> Long id = newRow.getLong(COLUMN_ID);
> statement.setLong(1, id);
> statement.execute();
> }
> }
>
> It would be so much nicer if I could return false from init(), indicating
> that I don't want this trigger running more than once in the current command.
> You know, the same as component.setValue(dontFireEvents) in the Swing API or
> really any other event/listener API I can think of.
>
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