Event Based Chain Step?

Question

For a couple days now I've been trying to come up with a working example of a Job Chain w/ an Inline Event for a Chain Step.
Would anyone happen to have a fairly simple example of this, or be able to point me in the right direction?
Thanks,
James

Answer 1

Hi James,
An inline event in a chain allows the chain to wait until an event is received before continuing with one or more branches of the chain. The way this works is that one of the chain steps is an event step which does nothing but wait for an event and completes successfully as soon as that event is received.
In a database events are represented by AQ messages to the chain event step waits until a message is received into a certain queue. Here is a simple complete example with comments. First step1 runs, then step 2 waits for an event . After the message is received, the final step3 runs and the chain completes. If you have any more questions, please reply.
Hope this helps,
Ravi.
-- ================= simple complete chain with event step example ==============
-- grant necessary privileges to scott
grant create job to scott ;
grant execute on dbms_aq to scott;
grant execute on dbms_aqadm to scott;
begin
dbms_rule_adm.grant_system_privilege
(dbms_rule_adm.CREATE_EVALUATION_CONTEXT_OBJ, 'scott', FALSE);
dbms_rule_adm.grant_system_privilege
(dbms_rule_adm.CREATE_RULE_SET_OBJ, 'scott', FALSE);
dbms_rule_adm.grant_system_privilege
(dbms_rule_adm.CREATE_RULE_OBJ, 'scott', FALSE);
end ;
connect scott/tiger
-- setup a multiple consumers queue for event messages
create or replace type msg_type as object ( col1 varchar2(20) ) ;
begin
dbms_aqadm.create_queue_table('qt1','msg_type',multiple_consumers => TRUE);
dbms_aqadm.create_queue ( queue_name => 'Q1', queue_table => 'QT1');
dbms_aqadm.start_queue ( queue_name => 'Q1' ) ;
end ;
-- create a scheduler program and chain
exec dbms_scheduler.create_program('prog1','plsql_block','null;',0,true);
begin
dbms_scheduler.create_chain('chain1');
dbms_scheduler.define_chain_step('chain1','step1','prog1');
dbms_scheduler.define_chain_event_step('chain1','step2',
'tab.user_data.col1 is not null', 'Q1');
dbms_scheduler.define_chain_step('chain1','step3','prog1');
dbms_scheduler.define_chain_rule('chain1','true','START step1');
dbms_scheduler.define_chain_rule('chain1','step1 completed', 'start step2');
dbms_scheduler.define_chain_rule('chain1','step2 completed','start step3');
dbms_scheduler.define_chain_rule('chain1','step3 completed','end');
dbms_scheduler.enable('chain1');
end;
-- now create the master chain job, and enable it so it runs immediately
exec dbms_scheduler.create_job('job1','chain','chain1',0,enabled=>true);
-- wait a second or two to let first step complete
select * from all_scheduler_job_log where job_name='JOB1' order by log_id;
-- observe that only first step has completed
-- now enqueue message to complete second step
declare
msg msg_type;
my_msgid RAW(16);
props dbms_aq.message_properties_t;
enqopts dbms_aq.enqueue_options_t;
begin
msg := msg_type('test');
dbms_aq.enqueue('q1', enqopts, props, msg, my_msgid);
end;
commit;
-- now check that chain has completed successfully
select * from all_scheduler_job_log where job_name='JOB1' order by log_id;
-- ======= end of complete inline event step example