Null Checks in Drools Decision Tables

Question

Is there any easier way to handle Null checks for parameters when using decision tables in drools? What i am trying to do is to migrate certain business rules in java to drools and so happens that the data is abstracted into multiple layers of objects. So unless i do a null check on them i am not able to proceed. Any suggestions are welcome. The business rule that i want to move to a decision table is of the form:

> When   new A().getB().getC().getData() > 0  then 
> System.out.println("Result found");

Its just too much of a pain to write a condition corresponding to null check of every field

Thanks in Advance.

laune laune · Accepted Answer · 2015-03-19T17:08:49

The existence of an object is a fundamental prerequisite for accessing its attributes. Thus, Drools isn't any worse than your run-of-the-mill Java code. Any technique that works in Java code is also applicable in Drools.

One simple way around this problem in Java is to introduce a method in class A: boolean isBCDataPositive().

Using Drools you can also write rules that will not proceed to evaluate when an object isn't present, e.g.

rule "is b.c.data positive"
when
    A( $b: B )
    B( this == $b, $c: c )
    C( this == $c, data > 0 )
then ... end

This requires the insertion of the contained objects A.b, A.b.c, provided they exist, but the rule will obviously be simple, also when using the spreadsheet notation.

Null Checks in Drools Decision Tables

1 Answers