geode-core/src/main/java/org/apache/geode/cache/query/SelectResults.java

/*
 * 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 java.util.Collection;
import java.util.List;
import java.util.Set;

import org.apache.geode.cache.query.types.CollectionType;
import org.apache.geode.cache.query.types.ObjectType;

/**
 * Contains the results of a {@linkplain org.apache.geode.cache.query.Query#execute() executing} a
 * <code>SELECT</code> expression within a query. A <code>SELECT</code> expression results in
 * <code>SelectResults</code> that contain instances of {@link Struct} if: (a) there is more than
 * one projection in the projection attributes, or (b) if the projection is <code>*</code> and there
 * is more than one collection specified in the <code>FROM</code> clause.
 * <p>
 *
 * Otherwise, a <code>SELECT</code> expression over a collection of domain objects results in
 * <code>SelectResults</code> that contain domain objects, i.e. instances of domain classes such as
 * {@link String} or <code>Address</code>.
 * <p>
 *
 * <pre>
 * QueryService qs = cacheView.getQueryService();
 *
 * String select = "SELECT DISTINCT * FROM /root/employees " + "WHERE salary > 50000";
 * Query query = qs.newQuery(select);
 * SelectResults results = query.execute();
 *
 * for (Iterator iter = results.iterator(); iter.hasNext();) {
 *   Employee emp = (Employee) iter.next();
 *   System.out.println("Highly compensated: " + emp);
 * }
 *
 * select = "SELECT DISTINCT age, address.zipCode FROM /root/employees " + "WHERE salary > 50000";
 * query = qs.newQuery(select);
 * results = query.execute();
 *
 * for (Iterator iter = results.iterator(); iter.hasNext();) {
 *   Struct struct = (Struct) iter.next();
 *   int age = ((Integer) struct.get("age")).intValue();
 *   String zipCode = (String) struct.get("zipCode");
 *   System.out.println(age + " -> " + zipCode);
 * }
 *
 * </pre>
 *
 * @see org.apache.geode.cache.query.Query#execute()
 *
 * @since GemFire 4.0
 */
public interface SelectResults<E> extends Collection<E> {

  /**
   * Return whether this collection is modifiable. The result of this method has no bearing on
   * whether the elements in the collection themselves are modifiable.
   *
   * @return true if this collection is modifiable, false if not.
   */
  boolean isModifiable();

  /**
   * Return the number of times element occurs in this collection, that is the number of duplicates
   * <code>element</code> has in this collection as defined by the <code>equals></code> method. If
   * <code>element</code> is not present in this collection, then 0 is returned.
   *
   * @param element the element
   * @return the number of occurrences of element
   * @since GemFire 5.1
   */
  int occurrences(E element);

  /**
   * Returns this <code>SelectResults</code> as a <code>java.util.Set</code>. If this collection is
   * distinct and unordered, then no copying is necessary. Otherwise, the contents of this
   * collection will be copied into a new instance of java.util.HashSet.
   *
   * @return Is this collection as a <code>java.util.Set</code>?
   */
  Set<E> asSet();

  /**
   * Returns this <code>SelectedResults</code> as a <code>java.util.List</code>. If this collection
   * is ordered, then no copying is necessary. Otherwise, the contents of this collection will be
   * copied into a new instance of java.util.ArrayList.
   *
   * @return this collection as a java.util.List
   */
  List<E> asList();

  /**
   * Return the ObjectType for the type of collection this represents.
   *
   * @return the CollectionType for the type of collection this represents
   */
  CollectionType getCollectionType();

  /**
   * Specify a new elementType, overriding any existing known elementType. This modifies the
   * CollectionType for this object to be the same collection type but with the newly specified
   * element type.
   *
   * @param elementType the new elementType
   */
  void setElementType(ObjectType elementType);

}