Elias Levy created FLINK-6420:
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Summary: Cleaner CEP API to specify conditions between events
Key: FLINK-6420
URL: https://issues.apache.org/jira/browse/FLINK-6420
Project: Flink
Issue Type: Improvement
Components: CEP
Affects Versions: 1.3.0
Reporter: Elias Levy
Priority: Minor
Flink 1.3 will introduce so-called iterative conditions, which allow the
predicate to look up events already matched by conditions in the pattern. This
permits specifying conditions between matched events, similar to a conditional
join between tables in SQL. Alas, the API could be simplified to specify such
conditions more declaratively.
At the moment you have to do something like
{code}
Pattern.
.begin[Foo]("first")
.where( first => first.baz == 1 )
.followedBy("next")
.where({ (next, ctx) =>
val first = ctx.getEventsForPattern("first").next
first.bar == next.bar && next => next.boo = "x"
})
{code}
which is not very clean. It would friendlier if you could do something like:
{code}
Pattern.
.begin[Foo]("first")
.where( first => first.baz == 1 )
.followedBy("next")
.relatedTo("first", { (first, next) => first.bar == next.bar })
.where( next => next.boo = "x" )
{code}
Something along these lines would work well when the condition being tested
against matches a single event (single quantifier).
If the condition being tested can accept multiple events (e.g. times
quantifier) two other methods could be used {{relatedToAny}} and
{{relatedToAll}}, each of which takes a predicate function. In both cases each
previously accepted element of the requested condition is evaluated against the
predicate. In the former case if any evaluation returns true the condition is
satisfied. In the later case all evaluations must return true for the
condition to be satisfied.
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