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Apache Geode provides a database-like consistency model, reliable transaction processing and a shared-nothing architecture to maintain very low latency performance with high concurrency processing

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/*
 * 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.geode.cache.query;

import org.apache.geode.cache.Operation;


/**
 * This interface provides methods to get all the information sent from the server about the CQ
 * event. The CqEvent is passed to the CQs CqListener methods. It can be used to retrieve such
 * information as the region operation, CQ operation associated with the event, the new key and
 * value from the event, and the CqQuery object associated with the event. The CqEvent is not an
 * extension of CacheEvent.
 * 
 * @since GemFire 5.5
 */
public interface CqEvent {

  /**
   * Get the CqQuery object of this event.
   * 
   * @see CqQuery
   * @return CqQuery object.
   */
  public CqQuery getCq();

  /**
   * Get the operation on the base region that triggered this event.
   * 
   * @return Operation operation on the base region (on which CQ is created).
   */
  public Operation getBaseOperation();

  /**
   * Get the operation on the query results. Supported operations include update, create, destroy,
   * region clear and region invalidate.
   * 
   * @return Operation operation with respect to CQ.
   */
  public Operation getQueryOperation();

  /**
   * Get the key relating to the event. In case of REGION_CLEAR and REGION_INVALIDATE operation, the
   * key will be null.
   * 
   * @return Object key.
   */
  public Object getKey();

  /**
   * Get the new value of the modification. If there is no new value returns null, this will happen
   * during delete operation. May throw InvalidDeltaException, if value is null and
   * Delta Propagation is enabled.
   * 
   * @return Object new/modified value.
   */
  public Object getNewValue();

  /**
   * If an error occurred, return the Throwable, otherwise return null. If an error occurred, then
   * this event will be passed to the onError method of the CqListener instead of the
   * onEvent method.
   * 
   * @return Throwable exception related to error.
   */
  public Throwable getThrowable();

  /**
   * Get the delta modification. If there is no delta, returns null. New value may still be
   * available.
   * 
   * @return byte[] delta value.
   * @since GemFire 6.5
   */
  public byte[] getDeltaValue();
}