org.iternine.jeppetto.dao.mongodb.projections.MapReduceCommand.java Source code

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Here is the source code for org.iternine.jeppetto.dao.mongodb.projections.MapReduceCommand.java

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/*
 * Copyright (c) 2011 Jeppetto and Jonathan Thompson
 *
 * 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
 *
 * 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.iternine.jeppetto.dao.mongodb.projections;

import org.iternine.jeppetto.dao.mongodb.enhance.DBObjectUtil;
import org.iternine.jeppetto.dao.mongodb.MongoDBCommand;

import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MapReduceOutput;

import java.util.Map;

/**
 * Base class for map reduce jobs.
 */
abstract class MapReduceCommand extends MongoDBCommand {

    //-------------------------------------------------------------
    // Variables - Private
    //-------------------------------------------------------------

    private DBObject query;

    //-------------------------------------------------------------
    // Constructor
    //-------------------------------------------------------------

    public MapReduceCommand(DBObject query) {
        this.query = query;
    }

    //-------------------------------------------------------------
    // Override - MongoDBCommand
    //-------------------------------------------------------------

    @Override
    public final Object singleResult(DBCollection dbCollection) {
        MapReduceOutput output = dbCollection.mapReduce(createMapFunction(), createReduceFunction(), null, query);
        DBCursor cursor = output.results();

        try {
            return transformToValue(cursor);
        } finally {
            output.drop();
        }
    }

    @Override
    public String toString() {
        return new StringBuilder(super.toString()).append(' ')
                .append(DBObjectUtil.toDBObject(Map.class, query.toMap())).toString();
    }

    //-------------------------------------------------------------
    // Methods - Protected
    //-------------------------------------------------------------

    protected Object defaultValue() {
        return null;
    }

    protected Object transformToValue(DBCursor dbCursor) {
        if (dbCursor.hasNext()) {
            return transformToValue(dbCursor.next());
        } else {
            return defaultValue();
        }
    }

    //-------------------------------------------------------------
    // Methods - Protected - Abstract
    //-------------------------------------------------------------

    protected abstract String createMapFunction();

    protected abstract String createReduceFunction();

    protected abstract Object transformToValue(DBObject obj);
}