Drools rules for this requirement

Question

I have xml similar to below:

<Beans>
        <Bean>
                <Type>D</Type> <!--type can be D, B, C-->  
           <Name>Dental</Name> 
           <Transaction>121</Transaction>  
           <Amount></Amount> 
        </Bean>
        <Bean>
           <Type>D</Type> <!--type can be D, B, C-->
           <Name>Dental</Name>
           <Transaction>12312</Transaction>
           <Amount>123.45</Amount>
         </Bean>
</Beans>

Business rules for this xml: For each bean, if type is D 1:Name shouldn't be null 2:Amount and transaction shouldn't be null 3: Amount and transaction should match existing values for the same transaction in database table. 4: If type is other than D, then there are different rules.

How do i represent this in Drools rule language.

Answer 1

My suggestion is to use one rule for each constraint:

rule "D Type - Name shouldnt be null"
when
    Bean(type == "D", name == null)
then
    //do whatever you want
end

... (you can figure out the other null checking rules)

rule "D Type - Amount must match DB value"
when
    $b: Bean(type == "D", amount != null)
    Double(doubleValue != $b.amount) from someGlobalService.getAmmount($b) 
then
    //do whatever you want
end

...

In the second rule I suggest to use a global service to retrieve the desired information from the DB and even implement some kind of cache. Another possibility could be to have the values from the db prepopulated in the ksession either as facts or globals.

Best Regards,