Java tutorial
/* * 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 com.mongodb.DBObject; /** * Map reduce job that computes the maximum field value. */ class MaximumMapReduceCommand extends MapReduceCommand { //------------------------------------------------------------- // Variables - Private //------------------------------------------------------------- private String field; //------------------------------------------------------------- // Constructor //------------------------------------------------------------- public MaximumMapReduceCommand(DBObject query, String field) { super(query); this.field = field; } //------------------------------------------------------------- // Override - MapReduceCommand //------------------------------------------------------------- @Override protected Object defaultValue() { return null; } @Override protected String createMapFunction() { return String.format("function() { emit( 1, this.%1$s ); }", field); } @Override protected String createReduceFunction() { return "function(k,v) { " + "var max; " + "for(var i in v) { " + " if (i == 0 || v[i] > max) { " + " max = v[i]; " + " } " + "} " + "return max; " + "}"; } @Override protected Object transformToValue(DBObject dbObject) { return dbObject.get("value"); } }