Hi Chao, Ad. 1 You could implement it with IterativeCondition. Sth like this:
Pattern<Event, ?> pattern = Pattern.<Event>begin("first").where(new
SimpleCondition<Event>() {
@Override
public boolean filter(Event value) throws Exception {
return value.equals("A") || value.equals("B");
}
}).followedBy("second").where(new IterativeCondition<Event>() {
@Override
public boolean filter(Event value, Context<Event> ctx) throws Exception {
return (value.equals("A") || value.equals("B")) &&
!value.equals(ctx.getEventsForPattern("first"));
}
}).
Ad. 2 Unfortunately right now as you said Pattern restarts each other event and
it is not possible to change that strategy. There is ongoing work to introduce
AfterMatchSkipStrategy[1], but at best it will be merged in 1.4.0. I did not
give it much thought, but I would try implement some discarding logic.
Regards,
Dawid
[1] https://issues.apache.org/jira/browse/FLINK-7169
> On 26 Jul 2017, at 22:45, Chao Wang <chaow...@wustl.edu> wrote:
>
> Hi,
>
> I have two questions regarding the use of the Flink CEP library
> (flink-cep_2.11:1.3.1), as follows:
>
> 1. I'd like to know how to use the API to express "emit event C in the
> presence of events A and B, with no restriction on the arriving order of A
> and B"? I've tried by creating two patterns, one for "A and then B" and the
> other for "B and then A", and consequently using two patternStreams to handle
> each case, which emits C. It worked but to me this approach seems redundant.
>
> 2. Given the above objective expression, how to consume the accepted events
> so that they will not be used for future matchings? For example, with the
> arriving sequence {A, B, A}, the CEP should only emit one C (due to the
> matching of {A,B}), not two Cs (due to {A,B} and {B,A}). Similarly, with the
> arriving sequence {B, A, B, A}, the CPE should only emit two Cs, not three.
>
>
> Thanks,
>
> Chao
>
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