| /* |
| * 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.druid.segment.join; |
| |
| import org.apache.druid.java.util.common.IAE; |
| import org.apache.druid.segment.column.ColumnHolder; |
| |
| import javax.annotation.Nullable; |
| import java.util.Comparator; |
| import java.util.List; |
| |
| /** |
| * Utility class for working with prefixes in join operations |
| */ |
| public class JoinPrefixUtils |
| { |
| private static final Comparator<String> DESCENDING_LENGTH_STRING_COMPARATOR = (s1, s2) -> |
| Integer.compare(s2.length(), s1.length()); |
| |
| /** |
| * Checks that "prefix" is a valid prefix for a join clause (see {@link JoinableClause#getPrefix()}) and, if so, |
| * returns it. Otherwise, throws an exception. |
| */ |
| public static String validatePrefix(@Nullable final String prefix) |
| { |
| if (prefix == null || prefix.isEmpty()) { |
| throw new IAE("Join clause cannot have null or empty prefix"); |
| } else if (isPrefixedBy(ColumnHolder.TIME_COLUMN_NAME, prefix) || ColumnHolder.TIME_COLUMN_NAME.equals(prefix)) { |
| throw new IAE( |
| "Join clause cannot have prefix[%s], since it would shadow %s", |
| prefix, |
| ColumnHolder.TIME_COLUMN_NAME |
| ); |
| } else { |
| return prefix; |
| } |
| } |
| |
| public static boolean isPrefixedBy(final String columnName, final String prefix) |
| { |
| return columnName.length() > prefix.length() && columnName.startsWith(prefix); |
| } |
| |
| /** |
| * Check if any prefixes in the provided list duplicate or shadow each other. |
| * |
| * @param prefixes A mutable list containing the prefixes to check. This list will be sorted by descending |
| * string length. |
| */ |
| public static void checkPrefixesForDuplicatesAndShadowing( |
| final List<String> prefixes |
| ) |
| { |
| // this is a naive approach that assumes we'll typically handle only a small number of prefixes |
| prefixes.sort(DESCENDING_LENGTH_STRING_COMPARATOR); |
| for (int i = 0; i < prefixes.size(); i++) { |
| String prefix = prefixes.get(i); |
| for (int k = i + 1; k < prefixes.size(); k++) { |
| String otherPrefix = prefixes.get(k); |
| if (prefix.equals(otherPrefix)) { |
| throw new IAE("Detected duplicate prefix in join clauses: [%s]", prefix); |
| } |
| if (isPrefixedBy(prefix, otherPrefix)) { |
| throw new IAE("Detected conflicting prefixes in join clauses: [%s, %s]", prefix, otherPrefix); |
| } |
| } |
| } |
| } |
| } |