oak-query-spi/src/main/java/org/apache/jackrabbit/oak/spi/query/Cursor.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.jackrabbit.oak.spi.query;

import java.util.Iterator;

import org.apache.jackrabbit.oak.api.Result.SizePrecision;

/**
 * A cursor to read a number of nodes sequentially.
 */
public interface Cursor extends Iterator<IndexRow> {

    /**
     * The next row within this index.
     * <p>
     * The row may only contains the path, if a path is available. It may also
     * (or just) contain so-called "pseudo-properties" such as "jcr:score" and
     * "rep:excerpt", in case the index supports those properties and if the
     * properties were requested when running the query. The query engine will
     * indicate that those pseudo properties were requested by setting an
     * appropriate (possibly unrestricted) filter condition.
     * <p>
     * The index should return a row with those properties that are stored in
     * the index itself, so that the query engine doesn't have to load the whole
     * row / node unnecessarily (avoiding to load the whole row is sometimes
     * called "index only scan"), specially for rows that are anyway skipped. If
     * the index does not have an (efficient) way to return some (or any) of the
     * properties, it doesn't have to provide those values. In this case, the
     * query engine will load the node itself if required. If all conditions
     * match, the query engine will sometimes load the node to do access checks,
     * but this is not always the case, and it is not the case if any of the
     * (join) conditions do not match.
     * 
     * @return the row
     */
    @Override
    IndexRow next();

    /**
     * Get the size if known.
     * 
     * @param precision the required precision
     * @param max the maximum nodes read (for an exact size)
     * @return the size, or -1 if unknown
     */
    long getSize(SizePrecision precision, long max);
    
}