Mapreduce two collections using Java

[Christopher Carver]

I read the following article on how to use mapreduce to join collections in MongoDB. I was able to perform the steps with no problems. Using the same tables from the article, I tried performing this task using Java.

However I am not getting the same results when porting this to Java and I'm not understanding why. The second mapReduce() call isn't doing anything. I get the "reduced" collection after the first call to mapReduce(), but the collection is not updated when make the second mapReduce() call; the dollars key is always 0.

Where am I going wrong? I tried different combinations to no avail. 

Thank you.

import com.mongodb.BasicDBObject;  

import com.mongodb.DB;  

import com.mongodb.DBCollection;  

import com.mongodb.DBObject;  

import com.mongodb.MapReduceCommand;  

import com.mongodb.MapReduceOutput;  

import com.mongodb.Mongo;  

  

public class MongoClient {  

  

 /** 

  * @param args 

  */  

 public static void main(String[] args) {  

  

  Mongo mongo;  

    

  try {  

   mongo = new Mongo("localhost", 27017);  

   DB db = mongo.getDB("mr_demo");  

  

   DBCollection life = db.getCollection("life_expectancy");  

   DBCollection econ = db.getCollection("us_economic_assistance");

   

   String map1 = "function() { " +

                 "emit(this.country, {life_expectancy: this.age, dollars: 0});" +

                 "}";

   

   String map2 = "us_econ_map = function() {" +

                 "  if (this.FY2009 !== undefined && this.FY2009 !== null) {"+

                 "    emit(this.country_name, {" +

                 "      dollars: this.FY2009," +

                 "      life_expectancy: 0" +

                 "    });" +

                 "  }" +

                 "}";

         

   String reduce = "function(key, values) { "+

                   "var result = {dollars: 0, life_expectancy: 0}; "+

                   "  values.forEach(function(value) { "+

                   "    result.dollars += (value.dollars !== null) ? value.dollars : 0;"+

                   "    if (result.life_expectancy === 0 && " +

                   "        value.life_expectancy !== null " +

                   "    ) { " +

                   "      result.life_expectancy = value.life_expectancy; " +

                   "    } " +

                   "  }); " +

                   "  return result; " +

                   "} ";

   

   

     

   MapReduceCommand cmd1 = new MapReduceCommand(life, map1, reduce,  

       "reduced", MapReduceCommand.OutputType.REPLACE, null);

   

   MapReduceCommand cmd2 = new MapReduceCommand(econ, map2, reduce,  

       "reduced", MapReduceCommand.OutputType.REDUCE, null);

  

   MapReduceOutput out1 = life.mapReduce(cmd1);  

   MapReduceOutput out2 = econ.mapReduce(cmd2);

    

   

  } catch (Exception e) {  

   // TODO Auto-generated catch block  

   e.printStackTrace();  

  }  

 }  

}  

[Christopher Carver]

Ugh.

I found the issue.

Original:

   String map2 = "us_econ_map = function() {" +

Replace:

 String map2 = "function() {" +

Sloppy copy and paste. 

[Canada Dennis Chen]

Thanks for posting ... This is what I looking for ... :-)

Christopher Carver於 2012年11月7日星期三 UTC-7上午11時02分15秒寫道：