| /* |
| * 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.flink.api.common.functions; |
| |
| import org.apache.flink.annotation.Public; |
| |
| import java.io.Serializable; |
| |
| /** |
| * Interface for Join functions. Joins combine two data sets by joining their |
| * elements on specified keys. This function is called with each pair of joining elements. |
| * <p> |
| * By default, the joins follows strictly the semantics of an "inner join" in SQL. |
| * the semantics are those of an "inner join", meaning that elements are filtered out |
| * if their key is not contained in the other data set. |
| * <p> |
| * The basic syntax for using Join on two data sets is as follows: |
| * <pre>{@code |
| * DataSet<X> set1 = ...; |
| * DataSet<Y> set2 = ...; |
| * |
| * set1.join(set2).where(<key-definition>).equalTo(<key-definition>).with(new MyJoinFunction()); |
| * }</pre> |
| * <p> |
| * {@code set1} is here considered the first input, {@code set2} the second input. |
| * <p> |
| * The Join function is an optional part of a join operation. If no JoinFunction is provided, |
| * the result of the operation is a sequence of 2-tuples, where the elements in the tuple are those that |
| * the JoinFunction would have been invoked with. |
| * <P> |
| * Note: You can use a {@link CoGroupFunction} to perform an outer join. |
| * |
| * @param <IN1> The type of the elements in the first input. |
| * @param <IN2> The type of the elements in the second input. |
| * @param <OUT> The type of the result elements. |
| */ |
| @Public |
| public interface JoinFunction<IN1, IN2, OUT> extends Function, Serializable { |
| |
| /** |
| * The join method, called once per joined pair of elements. |
| * |
| * @param first The element from first input. |
| * @param second The element from second input. |
| * @return The resulting element. |
| * |
| * @throws Exception This method may throw exceptions. Throwing an exception will cause the operation |
| * to fail and may trigger recovery. |
| */ |
| OUT join(IN1 first, IN2 second) throws Exception; |
| } |