| /* |
| * 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.persistence.graph; |
| |
| import java.util.Properties; |
| |
| /** |
| * Generic, directed, attributed Relation. |
| * <br> |
| * A relation is |
| * <ol> |
| * <LI>generic because Relation type is parameterized with the type of vertices it links. |
| * <LI>directed because it distinguishes the two vertices as source and target. |
| * <LI>attributed because any arbitrary key-value pair can be associated with a relation. |
| * </ol> |
| * <br> |
| * A relation is immutable in terms of its two vertices. The properties |
| * associated to a relation, however, can change. |
| * <br> |
| * @param <V1> the type of <em>source</em> vertex linked by this relation. |
| * @param <V2> the type of <em>target</em> vertex linked by this relation. |
| * |
| * @author Pinaki Poddar |
| * |
| */ |
| public interface Relation<V1,V2> { |
| /** |
| * Gets the immutable source vertex. |
| * |
| * @return a non-null source vertex. |
| */ |
| V1 getSource(); |
| |
| /** |
| * Gets the immutable target vertex. |
| * Unlike source, a target for a relation may be null. |
| * |
| * @return a target vertex. May be null. |
| */ |
| V2 getTarget(); |
| |
| |
| /** |
| * Adds the given key-value pair, overwriting any prior value associated to the same key. |
| * |
| * @return the same relation for <em>fluent</em> method-chaining |
| */ |
| Relation<V1,V2> addAttribute(String key, Object value); |
| |
| /** |
| * Affirms if an attribute value has been associated with the given key. |
| * |
| */ |
| boolean hasAttribute(String key); |
| |
| /** |
| * Gets the value of the given attribute. |
| * |
| * @return value of the given attribute. A null value does not distinguish whether |
| * the attribute was set to a null value or the attribute was absent. |
| * |
| * @see #hasAttribute(String) |
| */ |
| Object getAttribute(String key); |
| |
| /** |
| * Removes the given attribute. |
| * |
| * @return the modified relation for <em>fluent</em> method chaining. |
| */ |
| Relation<V1,V2> removeAttribute(String key); |
| |
| /** |
| * Gets the key-value pairs associated with this relation. |
| */ |
| Properties getAttributes(); |
| } |