[jboss-jira] [JBoss JIRA] Closed: (JBRULES-941) Add support to pluggable accumulate functions

[Edson Tirelli (JIRA)]

     [ http://jira.jboss.com/jira/browse/JBRULES-941?page=all ]

Edson Tirelli closed JBRULES-941.
---------------------------------

    Fix Version/s:  4.0.0.MR3
       Resolution: Done

Added support and a few out of the box functions:

average
sum
count
max
min

If needed, we add more functions later.


> Add support to pluggable accumulate functions
> ---------------------------------------------
>
>                 Key: JBRULES-941
>                 URL: http://jira.jboss.com/jira/browse/JBRULES-941
>             Project: JBoss Rules
>          Issue Type: Feature Request
>      Security Level: Public(Everyone can see) 
>            Reporter: Edson Tirelli
>         Assigned To: Edson Tirelli
>             Fix For:  4.0.0.MR3
>
>
>    All,
>    Today I used a few hours to develop something I think it is quite useful: the ability to have externally coded functions for accumulate. Basically, the idea is that common functions should have a predefined template and not be coded in every accumulate of every rule in your rule base.
>    Example: "average"
>    The idea is that instead of writing something like bellow in every rule:
> $avg : Number() from accumulate( Cheese( $price : price ),
>                                                    init( double total = 0; int count = 0 ),
>                                                    action( total += $price; count++; ),
>                                                    reverse( total -= $price; count--; ),
>                                                    result( new Double( total / count ) ) )
>      The user could simply use a predefined function like:
> $avg : Number() from accumulate( Cheese( $price : price ),
>                                                    average( $price ) );
>       Or if he wants to know how much will cost him to give 10% raise to all employees of a given department:
> $sum : Number() from accumulate( Employee( dept == "X", $salary : salary )
>                                                     sum( $salary * 0.1 ) )
>      And whatever the user wants to do.
>      So, instead of hardcoding a few functions, I thought it was better to let it pluggable. So I defined a simple interface (AccumulateFunction) and anyone willing to create an external function simply implement this interface and wires it using either the PackageBuilderConfiguration API or the configuration files mark created. Example:
> drools.accumulate.function.average = org.drools.base.accumulators.AverageAccumulator
>      Where "drools.accumulate.function." is a constant prefix and "average" is the function identifier the user will use in the rule file (DRL, XML, etc).
>      Also, we will provide common functions like "average", "sum", "count", "min", "max", etc, out of the box, since it is really easy to implement any function. Example: to implement the average function, all one needs to do is:
> package org.drools.base.accumulators;
> /**
>  * An implementation of an accumulator capable of calculating average values
>  *
>  * @author etirelli
>  *
>  */
> public class AverageAccumulator implements AccumulateFunction {
>     protected static class AverageData {
>         public int    count = 0;
>         public double total = 0;
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#createContext ()
>      */
>     public Object createContext() {
>         return new AverageData();
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#init(java.lang.Object)
>      */
>     public void init(Object context) throws Exception {
>         AverageData data = (AverageData) context;
>         data.count = 0;
>         data.total = 0;
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#accumulate (java.lang.Object, java.lang.Object)
>      */
>     public void accumulate(Object context,
>                            Object value) {
>         AverageData data = (AverageData) context;
>         data.count++;
>         data.total += ((Number) value).doubleValue();
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#reverse(java.lang.Object, java.lang.Object)
>      */
>     public void reverse(Object context,
>                         Object value) throws Exception {
>         AverageData data = (AverageData) context;
>         data.count--;
>         data.total -= ((Number) value).doubleValue();
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#getResult(java.lang.Object)
>      */
>     public Object getResult(Object context) throws Exception {
>         AverageData data = (AverageData) context;
>         return new Double( data.count == 0 ? 0 : data.total / data.count );
>     }
>     /* (non-Javadoc)
>      * @see org.drools.base.accumulators.AccumulateFunction#supportsReverse()
>      */
>     public boolean supportsReverse() {
>         return true;
>     }
> }

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://jira.jboss.com/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira