[Mondrian] Proposal for adding result post processor extension to spi

[Ajit Vasudeo Joglekar]

We have a scenario where we need to filter out rows and columns based on 
criteria such as, is the cell value result of a literal calculated member 
evaluation and whether the next position on the same axis isNull

Adding a extension point in RolapConnection (similar to 
DynamicSchemaProcessor) as below will allow post processing of the 
generated result. ResultPostProcessor implementation class could be a 
connection property similar to the DynamicSchemaProcessor

In RolapConnection - "public Result execute(Query query)" method


            for (int i = 0; i < query.axes.length; i++) {
                QueryAxis axis = query.axes[i];
                if (axis.isNonEmpty()) {
                    result = new NonEmptyResult(result, query, i);
                }
            }
+            try {
+                final Class<ResultPostProcessor> clazz =
+                (Class<ResultPostProcessor>)
+                    Class.forName(resultPostProcessorName);
+                final Constructor<ResultPostProcessor> ctor =
+                clazz.getConstructor();
+                final ResultPostProcessor resultPostProc = 
ctor.newInstance();
+                result = resultPostProc.postProcessResult(result, query);
+
+            } catch (Exception e) {
+                throw Util.newError(e, "loading ResultPostProcessor "
+                + resultPostProcessorName);
+            }
            if (LOGGER.isDebugEnabled()) {
                StringWriter sw = new StringWriter();
                PrintWriter pw = new PrintWriter(sw);
                result.print(pw);
                pw.flush();
                LOGGER.debug(sw.toString());
            }
            query.setQueryEndExecution();
            return result;

To effectively make use of information contained in the Result instance in 
the post processor it will be necessary to make certain class methods, 
members accessible as follows

public abstract class ResultBase
        protected final Axis[] axes; // remove final


class RolapCell implements Cell { // make public

RolapCell
private Member[] getMembers() { // make public


The ResultPostProcessor could be a simple interface as below

public interface ResultPostProcessor {
    public Result postProcessResult(Result result, Query query);
}

=========================


Requesting comments, suggestions

Thanks,
-Ajit











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