Calculating days/months/years between 2 dates in Drools

Question

I am trying to compare 2 dates (let's say Date1 and Date 2) from 2 different entities(let's say Entity1 and Entity2) using Guided Rules Editor.

Date1 is a variable from Entity1 and Date2 is a variable from Entity2

The rule I want to execute is -

Package com.rules.xyz;
import com.rules.xyz.Entity1;
import com.rules.xyz.Entity2;

When
{
Entity1.Date1 <= Entity2. Date2 + 7 Days
}

then <perform some action>

I want to apply the same rule for months and years, i.e., When Date1 <= Date2 + 6 Months, then perform some action.

I am using Drools Workbench 7.2.0 Final

Could you please suggest a solution for the same.

Answer 1

In my case I have created a function to be able to reuse it, so it is defined in a separate DRL file:

function Date workWithDates(Date date, String operator, int entity, int number) {
    if (date != null) {
        java.util.Calendar newCal = java.util.Calendar.getInstance();
        newCal.setTime(date);
        if (operator.equals("-")) { //normally we would add, except if we want to subtract
            number = -number;
        }
        if (entity == 1) { //years
            newCal.add(java.util.Calendar.YEAR, number);
        } else if (entity== 2) { //months
            newCal.add(java.util.Calendar.MONTH, number);       
        } else if (entity== 3) { //days
            newCal.add(java.util.Calendar.DATE, number);        
        } else if (entity== 4) { //hours
            newCal.add(java.util.Calendar.HOUR, number);        
        } else if (entity== 5) { //minutes
            newCal.add(java.util.Calendar.MINUTE, number);      
        } else if (entity== 6) { //seconds
            newCal.add(java.util.Calendar.SECOND, number);      
        }
        return newCal.getTime();    
    } else {
        return date;
    }
}

And in your DRL file where you would invoke this function you would use it like this:

when
    Entity2 ( $date2 : Date2 != null )
    Entity1 ( Date1 != null, Date1 <= (workWithDates($date2, "+", 3, 7)) )

If you opt to separate the function in a different file too, make sure it is in the same package. For example, I have defined all reusable functions in a 000 FUNCTION.drl