Drools：获取最近的3个事件

Question

我正在从事一个小型Drools项目，因为我想了解更多关于使用规则引擎的知识。我有一个名为Event的类，它有以下字段：

• <代码>字符串标记 可以是任何字符串的标记

我在我的知识库中插入了数百个事件实例，现在我想得到3个最近的事件，它们都标记为“OK”（确定）。我想出了以下代码，它可以工作：

rule "Three most recent events tagged with 'OK'"
when
    $e1 : Event( tag == "OK",
                 $millis1 : millis )
    $e2 : Event( tag == "OK",
                 millis < $millis1, $millis2 : millis )
    $e3 : Event( tag == "OK",
                 millis < $millis2, $millis3 : millis )

    not Event( tag == "OK",
               millis > $millis1 )
    not Event( tag == "OK",
               millis > $millis2 && millis < $millis1 )
    not Event( tag == "OK",
               millis > $millis3 && millis < $millis2 )
then
  # Do something with $e1.value, $e2.value and $e3.value
end

但是我有一种感觉，应该有更好的方法来做到这一点。这很冗长，不容易重复使用：如果我想获取具有值的五个最近事件怎么办

如何改进此代码？




Answer 1

我可以这样简化“非逻辑”

rule "Three most recent events tagged with 'OK'"
when
    $e1 : Event( tag == "OK")
    $e2 : Event( tag == "OK", millis < $e1.millis )
    $e3 : Event( tag == "OK", millis < $e2.millis )
    not Event( this != $e2, tag == "OK", $e3.millis < millis, millis < $e1.millis )
then
    System.out.printf("%s - %s - %s%n", $e1, $e2, $e3);
end

没有提到清理事件。通常这是可取的，因此您可以通过删除最后一个事件来实现相同的逻辑：

rule "Three most recent events tagged with 'OK'"
when
    $e1 : Event( tag == "OK")
    $e2 : Event( tag == "OK", millis < $e1.millis )
    $e3 : Event( tag == "OK", millis < $e2.millis )
then
    System.out.printf("%s - %s - %s%n", $e1, $e2, $e3);
    retract ($e3)
end

假设每秒插入一个事件，一个“OK”，另一个为空，测试如下：

@DroolsSession("classpath:/test3.drl")
public class PlaygroundTest {
    
    @Rule
    public DroolsAssert drools = new DroolsAssert();
    
    @Test
    public void testIt() {
        for (int i = 0; i < 10; i++) {
            drools.advanceTime(1, SECONDS);
            drools.insertAndFire(new Event(i % 2 == 0 ? "OK" : "", i));
        }
    }
}

所有三种变体将产生相同的触发逻辑：

00:00:01 --> inserted: Event[tag=OK,millis=0]
00:00:01 --> fireAllRules
00:00:02 --> inserted: Event[tag=,millis=1]
00:00:02 --> fireAllRules
00:00:03 --> inserted: Event[tag=OK,millis=2]
00:00:03 --> fireAllRules
00:00:04 --> inserted: Event[tag=,millis=3]
00:00:04 --> fireAllRules
00:00:05 --> inserted: Event[tag=OK,millis=4]
00:00:05 --> fireAllRules
00:00:05 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [Event, Event, Event]
OK4 - OK2 - OK0
00:00:06 --> inserted: Event[tag=,millis=5]
00:00:06 --> fireAllRules
00:00:07 --> inserted: Event[tag=OK,millis=6]
00:00:07 --> fireAllRules
00:00:07 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [Event, Event, Event]
OK6 - OK4 - OK2
00:00:08 --> inserted: Event[tag=,millis=7]
00:00:08 --> fireAllRules
00:00:09 --> inserted: Event[tag=OK,millis=8]
00:00:09 --> fireAllRules
00:00:09 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [Event, Event, Event]
OK8 - OK6 - OK4
00:00:10 --> inserted: Event[tag=,millis=9]
00:00:10 --> fireAllRules

带有窗口的变量：长度（3）也将处理最后3个OK事件。虽然开始时有所不同：1和2个first OK事件也会触发。如果会话不包含任何事件，它还会在开始时以空列表触发一次。根据文档，滑动窗口立即开始匹配，定义滑动窗口并不意味着规则必须等待滑动窗口“满”才能匹配。例如，计算窗口上事件属性的平均值的规则：长度（10）将立即开始计算平均值，对于没有事件，它将从0（零）开始，并将在事件逐一到达时更新平均值。

00:00:01 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[]
00:00:01 --> inserted: Event[tag=OK,millis=0]
00:00:01 --> fireAllRules
00:00:01 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[OK0]
00:00:02 --> inserted: Event[tag=,millis=1]
00:00:02 --> fireAllRules
00:00:03 --> inserted: Event[tag=OK,millis=2]
00:00:03 --> fireAllRules
00:00:03 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[OK0, OK2]
00:00:04 --> inserted: Event[tag=,millis=3]
00:00:04 --> fireAllRules
00:00:05 --> inserted: Event[tag=OK,millis=4]
00:00:05 --> fireAllRules
00:00:05 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[OK0, OK2, OK4]
00:00:06 --> inserted: Event[tag=,millis=5]
00:00:06 --> fireAllRules
00:00:07 --> inserted: Event[tag=OK,millis=6]
00:00:07 --> fireAllRules
00:00:07 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[OK2, OK4, OK6]
00:00:08 --> inserted: Event[tag=,millis=7]
00:00:08 --> fireAllRules
00:00:09 --> inserted: Event[tag=OK,millis=8]
00:00:09 --> fireAllRules
00:00:09 <-- 'Three most recent events tagged with 'OK'' has been activated by the tuple [InitialFactImpl, UnmodifiableRandomAccessList]
[OK4, OK6, OK8]
00:00:10 --> inserted: Event[tag=,millis=9]
00:00:10 --> fireAllRules

Answer 2

假设您使用的是STREAM事件处理模式，并且您的事件在流中排序：

rule "3 most recent events"
when
    accumulate( $e : Event( tag == "OK" ) over window:length(3),
                $events : collectList( $e ) )
then
    // $events is a list that contains your 3 most recent 
    // events by insertion order
end

=====编辑====

根据您下面的评论，以下是如何在Drools 5.4中实现您想要的：

declare window LastEvents
    Event() over window:length(3)
end

rule "OK events among the last 3 events"
when
    accumulate( $e : Event( tag == "OK" ) from window LastEvents,
                $events : collectList( $e ) )
then
    // $events is a list that contains the OK events among the last 3 
    // events by insertion order
end

只要仔细检查语法，因为我正在背诵，但它应该接近这个。