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https://issues.apache.org/jira/browse/FLINK-6197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15944738#comment-15944738
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ASF GitHub Bot commented on FLINK-6197:
---------------------------------------
Github user dawidwys commented on a diff in the pull request:
https://github.com/apache/flink/pull/3624#discussion_r108352961
--- Diff: docs/dev/libs/cep.md ---
@@ -124,13 +124,70 @@ val start : Pattern[Event, _] = Pattern.begin("start")
</div>
</div>
-Each state must have an unique name to identify the matched events later
on.
+Each state must have a unique name to identify the matched events later on.
Additionally, we can specify a filter condition for the event to be
accepted as the start event via the `where` method.
+These filtering conditions can be either an `IterativeCondition` or a
`SimpleCondition`.
+
+**Iterative Conditions:** This type of conditions can iterate over the
previously accepted elements in the pattern and
+decide to accept a new element or not, based on some statistic over those
elements.
+
+Below is the code for an iterative condition that accepts elements whose
name start with "foo" and for which, the sum
+of the prices of the previously accepted elements for a state named
"middle", plus the price of the current event, do
+not exceed the value of 5.0. Iterative condition can be very powerful,
especially in combination with quantifiers, e.g.
+`oneToMany` or `zeroToMany`.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+start.where(new IterativeCondition<SubEvent>() {
+ @Override
+ public boolean filter(SubEvent value, Context<SubEvent> ctx) throws
Exception {
+ if (!value.getName().startsWith("foo")) {
+ return false;
+ }
+
+ double sum = 0.0;
+ for (Event event : ctx.getEventsForPattern("middle")) {
+ sum += event.getPrice();
+ }
+ sum += value.getPrice();
+ return Double.compare(sum, 5.0) < 0;
+ }
+});
+{% endhighlight %}
+</div>
+
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+start.where(
--- End diff --
I was thinking of some more Scala way of coding it. Maybe:
```
Pattern.begin[Event]("abc").where(
(a, ctx) => {
lazy val sum =
ctx.getEventsForPattern("a").asScala.map(_.getPrice).sum
a.getName.startsWith("foo") && sum + a.getPrice < 5.0
}
)
```
Also I would try to make the Scala API more convenient. util.Iterable is
not what I would expect. Not sure though if know it is the right moment. We
could postpone it to redesigning the API.
> Add support for iterative conditions.
> -------------------------------------
>
> Key: FLINK-6197
> URL: https://issues.apache.org/jira/browse/FLINK-6197
> Project: Flink
> Issue Type: Bug
> Components: CEP
> Affects Versions: 1.3.0
> Reporter: Kostas Kloudas
> Assignee: Kostas Kloudas
> Fix For: 1.3.0
>
>
> So far, the {{where}} clause only supported simple {{FilterFunction}}
> conditions.
> With this, we want to add support for conditions where the an event is
> accepted not only based on its own properties, e.g. name, as it was before,
> but also based on some statistic computed over previously accepted events in
> the pattern, e.g. if the price is higher than the average of the prices of
> the previously accepted events.
> This in combination with the recently added quantifiers will allow for a lot
> more expressive patterns.
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