Drools - Find minimum Java 8 Local Date - java-8

Question

I am trying to find the minimum date from list of dates (Java 8) using accumulate function in Drools.
This is my rule:
rule "Print minimum Service Date from Bill Lines"
when
accumulate (
$lineItem : LineLevelData($dateOfService : dateOfService) ,
$epochDay : min($dateOfService.toEpochDay())
)
$minServiceDate : LocalDate() from LocalDate.ofEpochDay($epochDay)
then
System.err.println("Min. Service Date used in rules calculation : " + $minServiceDate);
end
This is the exception I get:
Unable to Analyse Expression LocalDate.ofEpochDay($epochDay):
[Error: unable to resolve method using strict-mode: java.time.LocalDate.ofEpochDay(java.lang.Comparable)]
[Near : {... LocalDate.ofEpochDay($epochDay) ....}]
^ : [Rule name='Print minimum Service Date from Bill Lines']
Obviously, I am missing some basics here. Can somebody help me to fix this one?
Drools version: 7.5.0
POJO:
public class LineLevelData{
LocalDate dateofService;
}
Update:
rule "Print minimum Service Date from Bill Lines"
when
accumulate ( $lineItem : LineLevelData ( $dateOfService : dateOfService ) ,
$epochDay : min($dateOfService.toEpochDay()) )
$epochLong : Number (longValue > 0 ) from $epochDay
$minServiceDate : LocalDate( ) from LocalDate.ofEpochDay($epochLong)
then
System.err.println("Min. Service Date used in rules calculation : " + $minServiceDate);
end
After adding the cast to Long, epoch is converted to Local date. Adding this in case if it helps someone looking for this.

Answer 1

I guess the problem is that Drools is not preserving the type of the min function is returning and it is treating it as a Comparable instead of as a long.
There are 3 ways you can solve this problem:
Create your own accumulate function to deal with LocalDate
Use an accumulate with inline code
Use the workaround bellow to force Drools to cast the Comparable back to LocalDate.
Workaround:
rule "Print minimum Service Date from Bill Lines"
when
$c: Comparable() from accumulate (
LineLevelData($dateOfService : dateOfService) ,
min($dateOfService)
)
$minServiceDate: LocalDate() from $c
then
System.err.println("Min. Service Date used in rules calculation : " +
$minServiceDate);
end
Hope it helps,