| /* |
| * 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.cassandra.distributed.api; |
| |
| import java.util.Iterator; |
| import java.util.List; |
| import java.util.function.Function; |
| import java.util.function.Predicate; |
| |
| /** |
| * A table of data representing a complete query result. |
| * <p> |
| * A <code>QueryResult</code> is different from {@link java.sql.ResultSet} in several key ways: |
| * |
| * <ul> |
| * <li>represents a complete result rather than a cursor</li> |
| * <li>returns a {@link Row} to access the current row of data</li> |
| * <li>relies on object pooling; {@link #hasNext()} may return the same object just with different data, accessing a |
| * {@link Row} from a previous {@link #hasNext()} call has undefined behavior.</li> |
| * <li>includes {@link #filter(Predicate)}, this will do client side filtering since Apache Cassandra is more |
| * restrictive on server side filtering</li> |
| * </ul> |
| * |
| * <h2>Unsafe patterns</h2> |
| * <p> |
| * Below are a few unsafe patterns which may lead to unexpected results |
| * |
| * <code>{@code |
| * while (rs.hasNext()) { |
| * list.add(rs.next()); |
| * } |
| * }</code> |
| * |
| * <code>{@code |
| * rs.forEach(list::add) |
| * }</code> |
| * <p> |
| * Both cases have the same issue; reference to a row from a previous call to {@link #hasNext()}. Since the same {@link Row} |
| * object can be used across different calls to {@link #hasNext()} this would mean any attempt to access after the fact |
| * points to newer data. If this behavior is not desirable and access is needed between calls, then {@link Row#copy()} |
| * should be used; this will clone the {@link Row} and return a new object pointing to the same data. |
| */ |
| public interface QueryResult extends Iterator<Row> |
| { |
| List<String> names(); |
| |
| default QueryResult filter(Predicate<Row> fn) |
| { |
| return QueryResults.filter(this, fn); |
| } |
| |
| default <A> Iterator<A> map(Function<? super Row, ? extends A> fn) |
| { |
| return new Iterator<A>() |
| { |
| @Override |
| public boolean hasNext() |
| { |
| return QueryResult.this.hasNext(); |
| } |
| |
| @Override |
| public A next() |
| { |
| return fn.apply(QueryResult.this.next()); |
| } |
| }; |
| } |
| } |