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Java idiomatic client for Google Cloud Datastore.

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/*
 * Copyright 2015 Google LLC
 *
 * 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.cloud.datastore;

/**
 * An implementation of a Google Cloud Datastore key-only query that can be constructed by providing
 * all the specific query elements.
 *
 * @see Datastore
 *     queries
 */
public final class KeyQuery extends StructuredQuery {

  private static final long serialVersionUID = 1187064062245269457L;

  /** A {@code KeyQuery} builder for queries that return {@link Key} results. */
  public static final class Builder extends StructuredQuery.BuilderImpl {

    Builder(KeyQuery query) {
      super(query);
    }

    Builder() {
      super(ResultType.KEY);
      setProjection(KEY_PROPERTY_NAME);
    }

    @Override
    Builder mergeFrom(com.google.datastore.v1.Query queryPb) {
      super.mergeFrom(queryPb);
      setProjection(KEY_PROPERTY_NAME);
      clearDistinctOn();
      return this;
    }

    @Override
    public KeyQuery build() {
      return new KeyQuery(this);
    }
  }

  KeyQuery(Builder builder) {
    super(builder);
  }

  @Override
  public Builder toBuilder() {
    return new Builder(this);
  }
}