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 *  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
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package org.apache.cayenne;

import java.util.List;

/**
 * Represents a result of query execution. It potentially contain a mix of update counts
 * and lists of selected values. Provides API somewhat similar to java.util.Iterator or
 * java.sql.ResultSet for scanning through the individual results.
 * <p>
 * An example of iterating through a response:
 * </p>
 * 
 * <pre>
 * QueryResponse response = context.performGenericQuery(query);
 * for (response.reset(); response.next();) {
 *     if (response.isList()) {
 *         List list = response.currentList();
 *         // ...
 *     }
 *     else {
 *         int[] updateCounts = response.currentUpdateCount();
 *         // ...
 *     }
 * }
 * </pre>
 * 
 * <p>
 * In case the structure of the result is known, and only a single list or an update count
 * is expected, there is a simpler API to access them:
 * </p>
 * 
 * <pre>
 * QueryResponse response = context.performGenericQuery(query);
 * List list = response.firstList();
 * int[] count = response.firstUpdateCount();
 * </pre>
 * 
 * @since 1.2
 * @author Andrus Adamchik
 */
public interface QueryResponse {

    /**
     * Returns a number of results in the response.
     */
    int size();

    /**
     * Returns whether current iteration result is a list or an update count.
     */
    boolean isList();

    /**
     * Returns a List under the current iterator position. Use {@link #isList()} to check
     * the result type before calling this method.
     */
    List<?> currentList();

    /**
     * Returns an update count under the current iterator position. Returned value is an
     * int[] to accommodate batch queries. For a regular update result, the value will be
     * an int[1]. Use {@link #isList()} to check the result type before calling this
     * method.
     */
    int[] currentUpdateCount();

    /**
     * Rewinds response iterator to the next result, returning true if it is available.
     */
    boolean next();

    /**
     * Restarts response iterator.
     */
    void reset();

    /**
     * A utility method for quickly retrieving the first list in the response. Returns
     * null if the query has no lists. Note that this method resets current iterator to an
     * undefined state.
     */
    @SuppressWarnings("unchecked")
    List firstList();

    /**
     * A utility method for quickly retrieving the first update count from the response.
     * Note that this method resets current iterator to an undefined state.
     */
    int[] firstUpdateCount();
}
