Pass parameter to ESPER EPL query?

Question

I am new to esper epl query.I want to know is it possible to change EPL query in run time.It means I have a form which can use to change the time length,number of records in ESPER.It is simply like this,increase the time length in epl query,number of records in event.Likewise i want to change parameter in pragmatically.I want to know is this possible and if yes give me some hint to start. Thanks

Answer 1

Depending on your actual requirement you can use Variables. From Esper Docs:

In addition to creating a variable via the create variable syntax, the runtime and engine configuration API also allows adding variables. The next code snippet illustrates the use of the runtime configuration API to create a string-typed variable:

epService.getEPAdministrator().getConfiguration().addVariable("myVar", String.class, "init value");

Then you can use variables in your queries. For instance (again from Esper docs):

The next statement assumes that a variable named 'var_threshold' was created to hold a total price threshold value. The statement outputs an event when the total price for a symbol is greater then the current threshold value:

 select symbol, sum(price) 
   from TickEvent  group by symbol having
   sum(price) > var_threshold

So if you exactly know what you want to parametrize, then you can make your queries more dynamic.