kodo.query
Interface AggregateListener

All Superinterfaces:

Serializable

All Known Subinterfaces:

JDBCAggregateListener

public interface AggregateListener

extends Serializable

An aggregate listener aggregates data produced by a JDOQL query.

Method Summary

Object	evaluate(Collection args, Collection candidates, KodoPersistenceManager pm) Return the value of this aggregate.
boolean	expectsArgument() Return whether this function expects to act on an argument.
String	getTag() Return the tag that this listener listens for.

Method Detail

getTag

public String getTag()

Return the tag that this listener listens for.

expectsArgument

public boolean expectsArgument()

Return whether this function expects to act on an argument. Some function may not need arguments; for example, a function to count the number of objects that match a given filter might be of the form: count().

evaluate

public Object evaluate(Collection args,
                       Collection candidates,
                       KodoPersistenceManager pm)

Return the value of this aggregate.

Parameters:

args - for each candidate, the value of the argument to the function; will be null if this aggregate does not expect an argument

candidates - the candidate objects being evaluated

pm - a persistence manager to use if needed

Returns:

the value of the aggregate

Throws:

JDOUserException - if this aggregate does not support in-memory operation