Under MongoDB java driver Mapreduce command scope; add functions to Scope

Question

Is their a way to Execute a MongoDB map reduce job through the java driver in which you create a scope DBObject that contains functions.

I can execute my map reduce configuration in javascript where the passed in scope contains utility functions, but I can't figure out how to do this with the java driver.

I setup the scope using mapReduceCommand's

c.addExtraOption("scope",new BasicDBObject().append('average',function(){ return false;}));

However I can't get the mappers/reducers to recognize the scope component 'e.g.' average as a function. If I use quotes, the map reduce context thinks its a String, but if not, I can't seem to make the scope component parse.

How does one get a function in the scope component through the java driver?

Thanks to Ren's answer, Here is a spring bean configuration to set up a scope for the mongodb java driver with a function.

    <util:map id="mrScope" 
              key-type="java.lang.String" 
              value-type="java.lang.Object">
    <entry key="buckets"><bean class="com.mongodb.util.JSON" factory-method="parse"><constructor-arg value="[0,10,15,20,25,30,35,40,45,50,55,60,65]"/></bean></entry>
    <entry key="average">
        <bean class="org.bson.types.CodeWScope">
            <constructor-arg value="function () {var s = 0;for (var i = 0; i &gt; arguments.length; i++) s += arguments[i];return s / arguments.length;}"/>
            <constructor-arg><bean class="org.bson.BasicBSONObject"/></constructor-arg>
        </bean>
    </entry>

Can you please provide more details like how to use a Map as scope object.. Is it possible ? — gsuresh92
– gsuresh92, Commented Dec 23, 2015 at 9:38

Ren · Accepted Answer · 2012-04-06 15:52:31Z

8

The server code automatically converts the map and reduce into Javascript function, but not so with scope. To pass a function in the scope option, you can do this instead:

c.addExtraOption("scope", new BasicBSONObject("average",
  new CodeWScope("function(){ return false;}", new BasicBSONObject())));

answered Apr 6, 2012 at 15:52

Ren

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1 Comment

Ron Tuffin Over a year ago

Thanks Ren. This part of Mongo is not as well documented as some would like :) So it is good to find the answers.

gsuresh92 · Accepted Answer · 2015-12-23 13:07:12Z

1

With the new api (3.0).. I found the below option is working

collection .mapReduce(map, reduce) .scope(new Document("key", value)) .limit(100);

answered Dec 23, 2015 at 13:07

gsuresh92

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Piotr Skoczek · Accepted Answer · 2016-10-17 13:12:49Z

For those who struggle with applying function in scope using MongoTemplate, example below seems to work:

    Map<String, Object> scopeVariables = new HashMap<>();
    String scopeFunction="function(){ //do something }";
    scopeVariables.put("transform", new CodeWScope(scopeFunction,new BasicBSONObject()));

    MapReduceOptions options = new MapReduceOptions();
    options.scopeVariables(scopeVariables);
    options.outputTypeInline();

    MapReduceResults<ValueObject> result = template.mapReduce("collection", mapFunction, reduceFunction, options, ValueObject.class);

After running code above, transform() function will be visible in map function:

var mapFunction=function(){  
  transform(); 
  emit(key,value); 
}

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