| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.openjpa.kernel.exps; |
| |
| import java.io.Serializable; |
| import java.util.Collection; |
| |
| import org.apache.openjpa.kernel.StoreContext; |
| |
| /** |
| * An aggregate listener aggregates data produced by an ExpressionQuery. |
| * |
| * @author Abe White |
| * @author Patrick Linskey |
| */ |
| public interface AggregateListener |
| extends Serializable { |
| |
| /** |
| * Return the tag that this listener listens for. |
| */ |
| public String getTag(); |
| |
| /** |
| * 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: |
| * <code>count()</code>. |
| */ |
| public boolean expectsArguments(); |
| |
| /** |
| * Return the value of this aggregate. |
| * |
| * @param 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 |
| * @param argClasses the expected class of each argument element |
| * @param candidates the candidate objects being evaluated |
| * @param ctx the persistence context |
| * @return the value of the aggregate |
| * @throws org.apache.openjpa.util.UserException if this aggregate does not |
| * support in-memory operation |
| */ |
| public Object evaluate(Collection args, Class[] argClasses, |
| Collection candidates, StoreContext ctx); |
| |
| /** |
| * Return the expected type of the result of this listener. |
| * |
| * @param argClasses the expected classes of the argument, or null if |
| * no arguments |
| */ |
| public Class getType(Class[] argClasses); |
| } |