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.DBCursor; import com.mongodb.DBObject; /** * Map reduce job that counts distinct field values. */ class CountDistinctMapReduceCommand extends MapReduceCommand { //------------------------------------------------------------- // Variables - Private //------------------------------------------------------------- private String field; //------------------------------------------------------------- // Constructor //------------------------------------------------------------- public CountDistinctMapReduceCommand(DBObject query, String field) { super(query); this.field = field; } //------------------------------------------------------------- // Override - MapReduceCommand //------------------------------------------------------------- @Override protected Integer defaultValue() { return 0; } @Override protected String createMapFunction() { return String.format("function() { emit( this.%1$s, 1 ); }", field); } @Override protected String createReduceFunction() { return "function(k,v) { " + "var sum=0; " + "for(var i in v) { " + " sum += v[i]; " + "} " + "return sum; " + "}"; } @Override protected Integer transformToValue(DBCursor dbCursor) { return dbCursor.count(); } @Override protected Integer transformToValue(DBObject dbObject) { throw new IllegalStateException("This method should not be invoked."); } }