Github user dawidwys commented on a diff in the pull request:
https://github.com/apache/flink/pull/4331#discussion_r132173699
--- Diff:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
---
@@ -150,6 +160,59 @@ long getWindowTime() {
}
/**
+ * Check pattern after match skip strategy.
+ */
+ private void checkPatternSkipStrategy() {
+ AfterMatchSkipStrategy afterMatchSkipStrategy =
currentPattern.getAfterMatchSkipStrategy();
+ if (afterMatchSkipStrategy.getStrategy() ==
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_FIRST ||
+ afterMatchSkipStrategy.getStrategy() ==
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_LAST) {
+ Pattern<T, ?> pattern = currentPattern;
+ while
(!pattern.getName().equals(afterMatchSkipStrategy.getPatternName())) {
+ pattern = pattern.getPrevious();
+ }
+ // pattern name match check.
+ if (pattern == null) {
+ throw new
MalformedPatternException("the pattern name specified in AfterMatchSkipStrategy
" +
+ "can not be found in the given
Pattern");
+ } else {
+ // can not be used with optional states.
+ if
(pattern.getQuantifier().hasProperty(Quantifier.QuantifierProperty.OPTIONAL)) {
+ throw new
MalformedPatternException("the AfterMatchSkipStrategy "
+ +
afterMatchSkipStrategy.getStrategy() + " can not be used with optional
pattern");
+ }
+ }
+
+ // start position check.
+ if (pattern.getPrevious() == null) {
--- End diff --
Had a second thought on all those cases, and I think you had a good point
with one of the previous proposals, just to fall back to the
`SKIP_TO_NEXT_EVENT`
Maybe let's allow all those situations, but if within a match we cannot
discard(e.g. skip is to the first pattern or the optional event is not present)
then we discard nothing. The advantage in my opinion it is easier to understand
than to understand and maintain all those cases. (As a side note the exceptions
in SQL in all those cases in my opinion are just an implementation details as
they keep a single partial match at a time). What do you think?
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