gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/server/ReviewDbUtil.java

// Copyright (C) 2016 The Android Open Source Project
//
// 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.google.gerrit.reviewdb.server;

import com.google.common.collect.Ordering;
import com.google.gwtorm.client.IntKey;

/** Static utilities for ReviewDb types. */
public class ReviewDbUtil {
  private static final Ordering<? extends IntKey<?>> INT_KEY_ORDERING =
      Ordering.natural().nullsFirst().<IntKey<?>>onResultOf(IntKey::get).nullsFirst();

  /**
   * Null-safe ordering over arbitrary subclass of {@code IntKey}.
   *
   * <p>In some cases, {@code Comparator.comparing(Change.Id::get)} may be shorter and cleaner.
   * However, this method may be preferable in some cases:
   *
   * <ul>
   *   <li>This ordering is null-safe over both input and the result of {@link IntKey#get()}; {@code
   *       comparing} is only a good idea if all inputs are obviously non-null.
   *   <li>{@code intKeyOrdering().sortedCopy(iterable)} is shorter than the stream equivalent.
   *   <li>Creating derived comparators may be more readable with {@link Ordering} method chaining
   *       rather than static {@code Comparator} methods.
   * </ul>
   */
  @SuppressWarnings("unchecked")
  public static <K extends IntKey<?>> Ordering<K> intKeyOrdering() {
    return (Ordering<K>) INT_KEY_ORDERING;
  }

  public static ReviewDb unwrapDb(ReviewDb db) {
    if (db instanceof DisallowReadFromChangesReviewDbWrapper) {
      return ((DisallowReadFromChangesReviewDbWrapper) db).unsafeGetDelegate();
    }
    return db;
  }

  private ReviewDbUtil() {}
}