java example using GroupOperation

[Marco Berri]

Hello everyone.

I would use the functionality of java .group mongo 3 you have any practical examples of how to use the class GroupOperation for perform this operations?

thank you.

my code

final MongoCollection<Document> nodesCollection = mongoDatabaseOneDms.getCollection("nodes");

BsonDocument keys = new BsonDocument("className", new BsonString("it.document"));

BsonDocument condition = new BsonDocument("stats", new BsonDocument("$exists", new BsonInt32(1)));

BasicDBObject initial = new BasicDBObject("totDownload", 0).append("totView", 0).append("totEle", 0);

BsonJavaScript reduceFunction = new BsonJavaScript("function(curr,result){}");


//THIS IS THE CAOS....
SingleServerBinding ss = new SingleServerBinding(null, null);

Codec<BsonDocument> decoder = new BsonDocumentCodec();

?? = new GroupOperation(nodesCollection, reduceFunction, Codec (????) ).key(keys).filter(condition).execute(ss);

[Ross Lawley]

Hi Marco,

In general the aggregation framework or even the mapReduce methods should be preferred over using the Group operation.  Can you explain what problem you are trying to achieve.  I hoping that using the aggregation framework will meet your needs and be faster!

Ross

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[Marco Berri]

Hi.

This is the script.

db.nodes.group(

{key : {'className':'it.marcoberri.Document'},

cond:{"stats" : {"$exists":1}},

reduce : function(curr, result){

if(curr.stats.downloads)

result.totDownload += curr.stats.downloads;

if(curr.stats.views)

result.totView += curr.stats.views;

result.totEle++;

},

initial : {totDownload : 0, totView : 0, totEle :0}}

);

I would try the .group function in java.

Tnx.

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[Marco Berri]

I'd like to use the .group transcoded in java.

example script with aggregate:

db.nodes.aggregate([

{

$match : {

className : "'it.marcoberri.Document",

stats : {$exists : 1}

}

},

{    

   $group: { 

_id: null,

downloads: { 

   $sum: "$stats.downloads"

},

views: { 

   $sum: "$stats.views"

},

count: { 

   $sum: 1

},

 

   } 

}

] );

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skype: marco.berri
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[Ross Lawley]

Hi Marco,

The Java driver provides builders to make this easy! See the Filters[1] and the Aggregation[2] builder documentation for more information:

Your example using these builders would be:

  import static com.mongodb.client.model.Aggregates.group

  import static com.mongodb.client.model.Accumulators.sum

  import static com.mongodb.client.model.Filters.and

  import static com.mongodb.client.model.Filters.eq

  import static com.mongodb.client.model.Filters.exists

  collection.aggregate(asList(

          match(and(eq("className", "it.marcoberri.Document"), exists("stats"))),

          group(null, asList(

                  sum("downloads", "$stats.downloads"),

                  sum("views", "$stats.views"),

                  sum("count", 1)))

  ));

Alternatively, you could provide Json and use Document.parse()[3] helper:

  collection.aggregate(asList(

    Document.parse("{ $match : { className : \"it.marcoberri.Document\",

             stats : {$exists : 1}}}"),

    Document.parse("{ $group: { 

        _id: null,

        downloads: { $sum: \"$stats.downloads\" },

        views: {  $sum: "$stats.views" },

   count: { $sum: 1 }

 } }"))

  );

I hope that helps!

Ross

[1] http://mongodb.github.io/mongo-java-driver/3.1/builders/filters/

[2] http://mongodb.github.io/mongo-java-driver/3.1/builders/aggregation/

[3] http://mongodb.github.io/mongo-java-driver/3.1/bson/extended-json/

[Marco Berri]

thanks , I finally used the aggregate function .

I would just like to know if the functionality of .group ( GroupOperation ) will be considered for future versions of the driver java .

It sounds very interesting !

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[Ross Lawley]

Currently, there are no plans to add it to the top level API. If you see the main documentation for MongoDB[1] you can see that alternatives are recommended (aggregation framework) because of the limitations. 

All the best, 

Ross

[1] https://docs.mongodb.org/manual/reference/method/db.collection.group/

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