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/*
 * Copyright 2021 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
 *
 *     https://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.appengine.api.datastore;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Identifies a callback method to be invoked before a {@link Query} for any of the specified kinds
 * is executed against the datastore. If {@link #kinds()} is not provided the callback will execute
 * for queries against all kinds, including kind-less queries. Methods with this annotation must
 * return {@code void}, must accept a single argument of type {@link PreQueryContext}, must not
 * throw any checked exceptions, must not be static, and must belong to a class with a no-arg
 * constructor. Neither the method nor the no-arg constructor of the class to which it belongs are
 * required to be public. Methods with this annotation are free to throw any unchecked exception
 * they like. Throwing an unchecked exception will prevent callbacks that have not yet been executed
 * from running, and the exception will propagate to the code that invoked the datastore operation
 * that resulted in the invocation of the callback. Throwing an unchecked exception from a callback
 * will prevent the datastore operation from executing.
 *
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface PreQuery {

  /**
   * The kinds to which this callback applies. The default value is an empty array, which indicates
   * that the callback should run for all kinds.
   *
   * @return The kinds to which this callback applies.
   */
  String[] kinds() default {};
}