/*
* Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
*
* Licensed 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 com.querydsl.core.group;
import com.querydsl.core.types.Expression;
/**
* Defines the way results of a given expression are grouped. GroupExpressions are also used
* to access values of a given GroupExpression within a Group.
* GroupExpressions are stateless wrappers for Expressions that know how to
* collect row values into a group.
*
* @param <T> Element type
* @param <R> Target type (e.g. List, Set)
*
* @author sasa
* @author tiwe
*/
public interface GroupExpression<T, R> extends Expression<R> {
/**
* Get the expression wrapped by this group definition
*
* @return wrapped expression
*/
Expression<T> getExpression();
/**
* Create a new GroupCollector to collect values belonging to this group.
*
* @return new GroupCollector
*/
GroupCollector<T, R> createGroupCollector();
}