Hi Folks,
I've been looking at triggers recently and was surprised to see that we
can't define Java code to execute as part of a trigger.
Note that we *can* use Java code, but we can't embed it in the trigger
definition like we can with an "ALIAS".
Would it be a good thing if we could store any Java code that could be used
within H2, within H2 itself?
The most flexible option seemed to be a new command. Something like this:
*CREATE CODE MyTriggerExample AS*
*$$*
*public void fire(Connection conn, Object[] oldRow, Object[] newRow) throws
SQLException {*
*
PreparedStatement prep = conn.prepareStatement("INSERT INTO
TEST_AUDIT(BLAH) VALUES (?)");
prep.setInt(1, (Integer)newRow[0] );
prep.execute();
prep.close();
*
*}*
*$$*
followed by
* CREATE TRIGGER TRIG_INS BEFORE INSERT ON TEST FOR EACH ROW CALL
"MyTriggerExample";*
*
*
Any "code" objects would also be able to be used in CREATE AGGREGATE, SET
DATABASE_EVENT_LISTENER, and
CREATE ALIAS commands.
Note that MyTriggerExample above does not require all org.h2.api.Trigger
interface methods to be implemented -- only
include the methods that are required by the end user.
The advantage of this is that triggers etc could be shipped as SQL, rather
than having to be put into a jar file and
included on the CLASSPATH of the H2 server.
I anticipate a single instance of each class being instantiated throughout
the life of the database, so implementation
classes would need to be threadsafe.
What do you think? (Especially Thomas :-)
I've actually got this mostly implemented, but before I spend any more time
on it I thought I'd better see if anybody
thought this added any value -- and if other databases did anything similar
in a nicer way.
Cheers
Kerry
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