org.apache.openjpa.kernel.exps
Interface AggregateListener

All Superinterfaces:

Serializable

All Known Subinterfaces:

JDBCAggregateListener

public interface AggregateListener
extends Serializable

An aggregate listener aggregates data produced by an ExpressionQuery.

Author:

Abe White, Patrick Linskey

Method Summary

Object	evaluate(Collection args, Class[] argClasses, Collection candidates, StoreContext ctx) Return the value of this aggregate.
boolean	expectsArguments() Return whether this function expects to act on arguments.
String	getTag() Return the tag that this listener listens for.
Class	getType(Class[] argClasses) Return the expected type of the result of this listener.

Method Detail

getTag

String getTag()

Return the tag that this listener listens for.

expectsArguments

boolean expectsArguments()

Return whether this function expects to act on arguments. 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

Object evaluate(Collection args,
                Class[] argClasses,
                Collection candidates,
                StoreContext ctx)

Return the value of this aggregate.

Parameters:

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

argClasses - the expected class of each argument element

candidates - the candidate objects being evaluated

ctx - the persistence context

Returns:

the value of the aggregate

Throws:

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

getType

Class getType(Class[] argClasses)

Return the expected type of the result of this listener.

Parameters:

argClasses - the expected classes of the argument, or null if no arguments