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espercomplex-event-processing

How do I get one output stream for several statements in Esper?

I'm new to Esper and I'm trying to get the results of multiple EPStatements to run through the same UpdateListener. For instance:

EPServiceProvider epService = EPServiceProviderManager.getDefaultProvider();
EPStatement avgStatement = epService.getEPAdministrator()
                        .createEPL("select avg(price) from OrderEvent.win:time(30 sec)");
EPStatement sumStatement = epService.getEPAdministrator()
                        .createEPL("select sum(price) from OrderEvent.win:time(60 sec)");

Is it possible to combine the results of both of those EPStatements into a separate statement? Something like: 

EPStatement bothStatements = epService.getEPAdministrator()
                            .createEPL("select * from avg(price), sum(price) where a.id=b.id");
bothStatements.addListener(listener);

I tried using inserting both statements into an Esper Named Window, but it seems like I can't do something like this where:

  • Event = (id, itemName, price)
  • Statement1 = (id, avg)
  • Statement2 = (id, sum)
  • Named Window = (id, avg, sum)

I would like to be able to combine the results of multiple statements and get a set of results (per event) into a single output stream.

Thanks for helping.

Solution

  • Did you consider that the same listener can be attached to two statements. What I means is "avgStatement.addListener(myListener)" and "sumStatement.addListener(myListener)".

    As an alternative you can use insert-into to populate the same stream. The would be like "insert into MyStream select avg(price) as avgPrice, 0 as sumPrice from ..." and "insert into MyStream select 0 as avgprice, sum(price) as sumPrice from ...".

    There is also the concept of a variant stream like variant types in visual basic. This lets you insert anything into a stream that is variant stream because variant streams don't need to be strongly typed.