按日期选择直接前置任务

Question

我是Drools的新手，我正在使用Drools 7.12.0来尝试和验证一组仪表读数，它们看起来像

public class MeterReading() {
    private long id;
    private LocalDate readDate;
    private int value;
    private String meterId
    private boolean valid;

/* Getters & Setters omitted */

}

作为验证的一部分，我需要通过readDate将每个MeterReading的值与其直接前身进行比较。

我第一次尝试使用'accumulate‘

when $mr: MeterReading()
  $previousDate: LocalDate() from accumulate(MeterReading($pdate: readDate < $mr.readDate ), max($pdate))

then
  System.out.println($mr.getId() + ":" + $previousDate);
end 

但随后发现这只返回前一个仪表读取的日期，而不是包含它的对象。然后我尝试了一个自定义的累积

when
$mr: MeterReading()

$previous: MeterReading() from accumulate(
      $p: MeterReading(id != $mr.id),
      init( MeterReading prev = null; ),

      action( if( prev == null ||  $p.readDate < prev.readDate) {
         prev = $p;
      }),
      result(prev))
 then
  System.out.println($mr.getId() + ":" + $previous.getId() + ":" + $previous.getReadDate());

 end

但这会选择仪表读数集中最早的读数，而不是直接的前一个读数。谁能给我指出正确的方向，我应该做什么或阅读，以便能够选择每个单独的仪表读取的直接前身。

问候

Answer 1

经过进一步的研究，我找到了这篇文章的http://planet.jboss.org/post/how_to_implement_accumulate_functions，我用它来编写我自己的累加函数；\

public class PreviousReadFinder  implements AccumulateFunction {
@Override

public Serializable createContext() {
  return new PreviousReadFinderContext();
}

@Override
public void init(Serializable context) throws Exception {
  PreviousReadFinderContext prfc = (PreviousReadFinderContext) context;
  prfc.list.clear();
}

@Override
public void accumulate(Serializable context, Object value) {
  PreviousReadFinderContext prfc = (PreviousReadFinderContext) context;
  prfc.list.add((MeterReading) value);
}

@Override
public void reverse(Serializable context, Object value) throws Exception {
  PreviousReadFinderContext prfc = (PreviousReadFinderContext) context;
  prfc.list.remove((MeterReading) value);
}

@Override
public Object getResult(Serializable context) throws Exception {
  PreviousReadFinderContext prfc = (PreviousReadFinderContext) context;
  return prfc.findLatestReadDate();
}

@Override
public boolean supportsReverse() {
  return true;
}

@Override
public Class<?> getResultType() {
  return MeterReading.class;
}

@Override
public void writeExternal(ObjectOutput out) throws IOException {

}

@Override
public void readExternal(ObjectInput in) throws IOException,  ClassNotFoundException {

}

private static class PreviousReadFinderContext implements Serializable {
    List<MeterReading> list = new ArrayList<>();

public Object findLatestReadDate() {

Optional<MeterReading> optional =  list.stream().max(Comparator.comparing(MeterReading::getReadDate));
if (optional.isPresent()) {
  MeterReading to = optional.get();
  return to;
}
  return  null;
}
 }
}

我的规则是

rule "Opening Read With Previous"

  dialect "mvel"

  when $mr: MeterReading()
       $pmr: MeterReading() from accumulate($p: MeterReading(readDate < $mr.readDate ), previousReading($p))

then
  System.out.println($mr.getId() + ":" + $pmr.getMeterReadDate());
end

我如何编写一条规则来选择集合中没有先前读数的最大的仪表读数？